The Millennium Ecosystem Assessment focuses on the benefits people obtain from ecosystems and aims to improve ecosystem management and contribute to human well-being and poverty alleviation

Nobody questions the importance of good scientific information for sound environmental decision-making. But designing mechanisms to link scientific research to the decision-making process is no easy matter. Research and decision-making often seem to operate in different worlds. Policy-makers' needs for applied findings and best judgment typically clash with scientists' pursuit of basic research and statistical significance.Despite this challenge, as needs for scientific input into decision-making arise, a number of institutions have been established to help bridge the science–policy divide. Regulatory agencies like the United States' Food and Drug Administration have met this need in areas of public health, for example, and Environmental Impact Assessment procedures have helped to introduce better science into project-level decisions. At the scale of global environmental challenges, highly regarded mechanisms have been established such as the Scientific Assessment of Ozone Depletion, which has guided decisions by governments, the private sector, and nongovernmental organizations (NGOs), and the Intergovernmental Panel on Climate Change, which has become the authoritative source of policy-relevant information on climate science.But a significant gap remains in the landscape of institutions designed to link science with policy-making: no mechanism has existed to provide decision-makers with authoritative information on the causes and consequences of changes in the planet's ecosystems and on the options for response.Human well-being and progress toward sustainable development are vitally dependent upon improving the management of Earth's ecosystems to ensure their conservation and sustainable use. The benefits that human beings extract from nature are the foundation of all economies and the basis of major industries, are sources of knowledge, and are central to many cultures. While demands for ecosystem services such as food and clean water are growing, human actions are at the same time diminishing the capability of many ecosystems to meet these demands. And while many of the changes to ecosystems, such as increased agricultural production, have greatly enhanced human well-being, many others have not. World fisheries are now declining due to overfishing, for instance, and some 40% of agricultural land has been degraded in the past half-century. Other human-induced impacts on ecosystems include alteration of the nitrogen, phosphorous, sulfur, and carbon cycles, causing acid rain, algal blooms, and fish kills in rivers and coastal waters, along with contributions to climate change.The benefits that human beings extract from nature are the foundation of all economies and the basis of major industries, are sources of knowledge, and are central to many cultures.The benefits that human beings extract from nature are the foundation of all economies and the basis of major industries, are sources of knowledge, and are central to many cultures.Recognizing the growing scale of these problems, United Nations Secretary General Kofi Annan, in his 2000 Millennium Report to the General Assembly, called for a Millennium Assessment of Global Ecosystems to provide definitive information on the consequences of ecosystem change for human well-being. With further authorization received through three international conventions (on Biological Diversity, Desertification, and Wetlands) and with financial support from the Global Environment Facility, the United Nations Foundation, the David and Lucile Packard Foundation, and the World Bank, the Millennium Ecosystem Assessment (MA) ( www.millenniumassessment.org ) was launched one year later, in 2001. More than 700 authors from 80 countries are now involved in the expert working groups preparing the global assessment; 100 experts will serve on the Editorial Review Board; more than 1,000 experts will be asked to review the materials, and hundreds more are undertaking subglobal assessments as part of the MA.The MA focuses on ecosystem services (the benefits people obtain from ecosystems), how changes in ecosystem services have affected human well-being, how ecosystem changes may affect people in future decades, and response options that might be adopted at local, national, or global scales to improve ecosystem management and thereby contribute to human well-being and poverty alleviation ( Figure 1 ).The first report— Ecosystems and Human Well-Being: A Framework for Assessment —was published in 2003 and describes the approach and methods used in the MA. The four main assessment volumes—Conditions and Trends, Scenarios, Response Options, and Subglobal Assessments—began the first of two rounds of peer review in January 2004, and the final assessment reports will be published in early 2005.Ecosystems and Human Well-Being: A Framework for AssessmentUnlike previous global scientific assessments, the MA is a “multiscale” assessment. Assessments at subglobal scales are needed because ecosystems are highly differentiated in space and time and because sound management requires careful local planning and action. Local assessments alone are insufficient, however, because some processes are global and because local goods, services, matter, and energy are often transferred across regions. The MA subglobal assessments will directly meet needs of decision-makers at the scale at which they are undertaken, strengthen the global findings with on-the-ground reality, and reinforce the local findings with global perspectives, data, and models.In Southern Africa, for example, a series of community-level assessments are being conducted using the MA conceptual framework. The findings from these assessments inform, and are informed by, assessments underway in the Gariep and Zambezi river basins. These local and river basin assessments, in turn, are linked to a regional assessment encompassing the countries in the Southern African Development Community. Other subglobal assessments are now underway in such regions as São Paulo, Brazil; coastal British Columbia, Canada; the Caribbean Sea; western China; Colombia; the Sinai Peninsula, Egypt; several regions within India; Indonesia; the Laguna Lake Basin, the Philippines; Portugal; and Sweden.The ultimate impact of the MA will depend on its credibility, legitimacy, and utility. To ensure its scientific credibility, the assessment involves leading scientists from around the world and has established an independent peer-review process. To ensure the political legitimacy, all of the stakeholders—governments, the private sector, and NGOs—have a role in governing the process, and governments themselves have approved the process through decisions in international conventions. And, to ensure its utility, ongoing interactions with stakeholders are designed to ensure a focus on their questions and issues.The scientific information now available concerning ecosystems and human development holds the promise of significantly improving the choices that the public and decision-makers take concerning the environment. But for that promise to be fulfilled, a bridge needs to be built between the research community holding this information and the decision-makers seeking it. The MA is an attempt to establish that bridge.


Background This study uses cigarette price elasticity to evaluate the effect of a new excise tax increase on cigarette consumption and to investigate responses from various types of smokers.
Background
This study uses cigarette price elasticity to evaluate the effect of a new excise tax increase on cigarette consumption and to investigate responses from various types of smokers.Methods Our sample consisted of current smokers between 17 and 69 years old interviewed during an annual face-to-face survey conducted by Taiwan National Health Research Institutes between 2000 to 2003. We used Ordinary Least Squares (OLS) procedure to estimate double logarithmic function of cigarette demand and cigarette price elasticity.
Methods
Our sample consisted of current smokers between 17 and 69 years old interviewed during an annual face-to-face survey conducted by Taiwan National Health Research Institutes between 2000 to 2003. We used Ordinary Least Squares (OLS) procedure to estimate double logarithmic function of cigarette demand and cigarette price elasticity.Results In 2002, after Taiwan had enacted the new tax scheme, cigarette price elasticity in Taiwan was found to be -0.5274. The new tax scheme brought about an average annual 13.27 packs/person (10.5%) reduction in cigarette consumption. Using the cigarette price elasticity estimate from -0.309 in 2003, we calculated that if the Health and Welfare Tax were increased by another NT$ 3 per pack and cigarette producers shifted this increase to the consumers, cigarette consumption would be reduced by 2.47 packs/person (2.2%). The value of the estimated cigarette price elasticity is smaller than one, meaning that the tax will not only reduce cigarette consumption but it will also generate additional tax revenues. Male smokers who had no income or who smoked light cigarettes were found to be more responsive to changes in cigarette price.
Results
In 2002, after Taiwan had enacted the new tax scheme, cigarette price elasticity in Taiwan was found to be -0.5274. The new tax scheme brought about an average annual 13.27 packs/person (10.5%) reduction in cigarette consumption. Using the cigarette price elasticity estimate from -0.309 in 2003, we calculated that if the Health and Welfare Tax were increased by another NT$ 3 per pack and cigarette producers shifted this increase to the consumers, cigarette consumption would be reduced by 2.47 packs/person (2.2%). The value of the estimated cigarette price elasticity is smaller than one, meaning that the tax will not only reduce cigarette consumption but it will also generate additional tax revenues. Male smokers who had no income or who smoked light cigarettes were found to be more responsive to changes in cigarette price.Conclusions An additional tax added to the cost of cigarettes would bring about a reduction in cigarette consumption and increased tax revenues. It would also help reduce incidents smoking-related illnesses. The additional tax revenues generated by the tax increase could be used to offset the current financial deficiency of Taiwan's National Health Insurance program and provide better public services.
Conclusions
An additional tax added to the cost of cigarettes would bring about a reduction in cigarette consumption and increased tax revenues. It would also help reduce incidents smoking-related illnesses. The additional tax revenues generated by the tax increase could be used to offset the current financial deficiency of Taiwan's National Health Insurance program and provide better public services.

Background One of the problems in controlling tobacco in Taiwan is that cigarette prices are lower in Taiwan than in most countries [ 1 , 2 ]. In India, smokers have to work 77 minutes to afford a pack of cigarettes, in Indonesia 62 mins, in China 56 mins, but in Taiwan they need only work 7 to 10 mins to afford a pack [ 1 ]. As long as the domestic cigarette price remains rather low, we probably will not see much of a decrease in the number of smokers. The smoking population increased to 4.5 million persons (total population 22,520,776) in 2002 [ 3 ]. One out of three adults smoked. Currently, due to illnesses and death associated with cigarette smoking, smokers currently account for approximately 20 billion NT dollar of extra medical expense annually and account for a 160 billion NT dollar loss in GDP (Gross Domestic Product)[ 4 ]. This economic burden in putting pressure on the government to further increase the existing Health and Welfare Tax on tobacco. Because high excise taxes on cigarettes have been found able to reduce cigarette consumption [ 5 - 8 ], such measures are becoming one of the most important means of controlling tobacco [ 9 - 11 ]. The new tax scheme enacted on 1 January 2002 in Taiwan resulted in NT $16.8 tax excise. This tax included the existing taxes for NT $11.8 and a NT $5 Health & Welfare Tax for a 20-pack of cigarettes. The government also levies 5% sales taxes. Under that tax scheme, the cigarette tax revenues account for 40% of the retail price, which is about NT $42.2. While 40% sounds high, it is actually lower than the taxes imposed on cigarettes in developed countries that have seen some success at lowering cigarette consumption. The government should take elasticity of demand into consideration when deciding whether to increase or add an excise tax levy. If there is a price elasticity below 1, a tax increase brings about a decline in consumption and an increase in total tax revenues. Since Hsieh, Hu and Lin (1999) found that figure to be -0.6 in Taiwan, it can be reasonable to assume that a tax increase would be more likely to reduce cigarette consumption more significantly in Taiwan than in other countries with lower price elasticities at least in the short-term and medium term [ 12 ]. Higher taxes would also generate higher total tax revenues. Taiwan's Tobacco and Wine Tax Law is currently under review in the Legislative Yuan of Taiwan. Some legislators are seeking to increase the Tobacco Health and Welfare Tax by NT $3 per pack, raising it from NT $5 to NT $8 per pack. Just as they have done in the past, cigarette sellers will probably shift the tax increase to the consumers letting them be responsible for the increase. The effect of the price increase on demand depends on cigarette price elasticity – the larger the elasticity, the larger the reduction in consumption. Therefore, an estimation of price elasticity for domestic cigarettes could be a very important indicator of the possible effect a "Tobacco Health and Welfare Tax" would have on cigarette consumption and could be used to adjust Tobacco Health and Welfare Tax accordingly. Price elasticity of cigarette in Taiwan has been mostly estimated using time-series data [ 12 , 13 ], though this method might overlook the impact of smuggled cigarettes on the price elasticity and overestimate the price elasticity. It might be more appropriate and useful to use cross-section data from the Health Interview Survey to estimate the effect of cigarette tax on cigarette consumption and to compare differences in cigarette price elasticity with various smoker characteristics.
Background
One of the problems in controlling tobacco in Taiwan is that cigarette prices are lower in Taiwan than in most countries [ 1 , 2 ]. In India, smokers have to work 77 minutes to afford a pack of cigarettes, in Indonesia 62 mins, in China 56 mins, but in Taiwan they need only work 7 to 10 mins to afford a pack [ 1 ]. As long as the domestic cigarette price remains rather low, we probably will not see much of a decrease in the number of smokers.The smoking population increased to 4.5 million persons (total population 22,520,776) in 2002 [ 3 ]. One out of three adults smoked. Currently, due to illnesses and death associated with cigarette smoking, smokers currently account for approximately 20 billion NT dollar of extra medical expense annually and account for a 160 billion NT dollar loss in GDP (Gross Domestic Product)[ 4 ]. This economic burden in putting pressure on the government to further increase the existing Health and Welfare Tax on tobacco.Because high excise taxes on cigarettes have been found able to reduce cigarette consumption [ 5 - 8 ], such measures are becoming one of the most important means of controlling tobacco [ 9 - 11 ]. The new tax scheme enacted on 1 January 2002 in Taiwan resulted in NT $16.8 tax excise. This tax included the existing taxes for NT $11.8 and a NT $5 Health & Welfare Tax for a 20-pack of cigarettes. The government also levies 5% sales taxes. Under that tax scheme, the cigarette tax revenues account for 40% of the retail price, which is about NT $42.2. While 40% sounds high, it is actually lower than the taxes imposed on cigarettes in developed countries that have seen some success at lowering cigarette consumption.The government should take elasticity of demand into consideration when deciding whether to increase or add an excise tax levy. If there is a price elasticity below 1, a tax increase brings about a decline in consumption and an increase in total tax revenues. Since Hsieh, Hu and Lin (1999) found that figure to be -0.6 in Taiwan, it can be reasonable to assume that a tax increase would be more likely to reduce cigarette consumption more significantly in Taiwan than in other countries with lower price elasticities at least in the short-term and medium term [ 12 ]. Higher taxes would also generate higher total tax revenues.Taiwan's Tobacco and Wine Tax Law is currently under review in the Legislative Yuan of Taiwan. Some legislators are seeking to increase the Tobacco Health and Welfare Tax by NT $3 per pack, raising it from NT $5 to NT $8 per pack. Just as they have done in the past, cigarette sellers will probably shift the tax increase to the consumers letting them be responsible for the increase. The effect of the price increase on demand depends on cigarette price elasticity – the larger the elasticity, the larger the reduction in consumption. Therefore, an estimation of price elasticity for domestic cigarettes could be a very important indicator of the possible effect a "Tobacco Health and Welfare Tax" would have on cigarette consumption and could be used to adjust Tobacco Health and Welfare Tax accordingly.Price elasticity of cigarette in Taiwan has been mostly estimated using time-series data [ 12 , 13 ], though this method might overlook the impact of smuggled cigarettes on the price elasticity and overestimate the price elasticity. It might be more appropriate and useful to use cross-section data from the Health Interview Survey to estimate the effect of cigarette tax on cigarette consumption and to compare differences in cigarette price elasticity with various smoker characteristics.Methods This study uses data on current smokers from 17 to 69 years of age during years 2000 to 2003. First, the demand function of the current smokers was established. Respondents who answered "everyday" or "some of the days" to the question how often you smoke were classified as "current smokers". Then, we used a random sampling of how they consumed and how much they paid for it between 2000 to 2003 to calculate cigarette price elasticity. We then analyzed differences in cigarette price elasticity in smokers categorized according to gender, age, education, income standard, and how much they smoked. Demand function Cigarette demand function was estimated by OLS and expressed by double logarithm function. The estimated demand function we used was: ln  Q ig  =  α 0  +  β 1  ln  P ig  +  γ 2  ln  I ig      (1) where lnQ ig  is i'th current smokers' logarithm representing monthly amount smokers consumed per person in group g. Current smokers were categorized according to age, gender, education, monthly income, and amount smoked. lnP ig  is i'th current smokers' logarithm representing cigarette price per pack (NT$) for smoking characteristics group g. lnI ig  is i'th current smokers' logarithm representing income per capita (NT$) for various categories of smokers in group g. The  α 0 ,  β 1 , and  γ 2  are parameters to be estimated. In order to measure how price change might affect cigarette consumption, the determination of price elasticity was particularly important. Price elasticity of demand for cigarettes is defined as the percent change in consumption resulting from a price increase. Cigarette price elasticity of demand  β 1  and income elasticity of demand  γ 2  can be derived from logarithmically differentiation (1) according to price and income. Data collection Using an annual face-to-face survey on cigarette consumption from 2000 to 2003 by Taiwan National Health Research Institutes, we collected data on how many packs current smokers consumed, how much they paid for a pack of cigarettes, how much they earned per month and how much they spent on cigarettes per month. Current smokers were categorized into gender, age, education, income, and amount smoked. Calculations of cigarette price were based on the average retail price of the top 3 most consumed cigarettes, calculations of number of packs smoked per month were done by dividing the monthly cigarette consumption by the average retail price. Calculations of income were based on personal monthly income. Certain background characteristics are listed in Table  1 . More than 90% of the smokers were men; less than 10% women. The numbers of young smokers were rising at the time of the study. Young people between the ages of 17 and 24 years old made up 5.4% of the sample in 2000, while they made up 12.8% in 2003, a 1.4 percent increase. The number of elderly smokers above the age of 55 gradually declined from 15.5% in 2000 to 10.8% in 2003. People with higher educational backgrounds tended to smoke more. More than 60% of the current smokers had senior or junior high school educations between 2000 and 2002. Second only to smokers with senior high school degrees, the percentage of the smokers with college degree increased by 27.2% in 2003, accounting for almost 40% of all the smokers. Thirty-five to forty percent earned between NT $20,000 to NT $30,000 per month. Those who smoked less than one pack were defined as light smokers; 1~2 packs (2 packs excluded), medium smokers; and 2 packs and above, heavy smokers. The proportion of light smokers had gradually increased from 50% in 2000 to 60% in 2003, and the proportion of heavy smokers gradually decreased from 11.8% in 2000 to 6.5% in 2003, showing an overall tendency toward reducing consumption. Table 1 Background characteristics of the current smokers in Taiwan, 2000–2003 2000 2001 2002 2003 Characteristics No. % No. % No. % No. % Total 856 632 521 493 Gender  Male 789 92.2 599 94.8 496 95.0 460 93.3  Female 67 7.8 33 5.2 25 5.0 33 6.7 Age  17–24 46 5.4 35 5.5 41 7.9 63 12.8  25–34 179 20.9 133 21.0 94 18.0 101 20.5  35–44 299 34.9 222 35.1 190 36.5 177 35.9  45–54 199 23.2 149 23.6 122 23.4 99 20.1  55- 133 15.5 93 14.7 74 14.2 53 10.8 Education  College and above 168 19.6 128 20.3 107 20.5 134 27.2  Senior high school 317 37.0 245 38.8 195 37.4 196 39.8  Junior high school 216 25.2 153 24.2 136 26.1 98 19.9  Primary school or lower 155 18.1 106 16.8 83 15.9 65 13.2 Month income   No income 98 11.4 93 14.7 63 12.1 75 15.2   <NT $20,000 146 17.1 94 14.9 94 18.0 84 17.0  NT $ 20,000–39,999 335 39.1 237 37.5 192 36.9 174 35.3  NT $ 40,000–59,999 181 21.1 144 22.8 117 22.5 105 21.3  ≥ NT $ 60,000 96 11.2 64 10.1 55 10.6 55 11.2 Smoking degree   Light smokers 445 50.0 319 50.5 281 53.9 296 60.0  Medium smokers 310 36.2 250 39.6 200 38.4 165 33.5  Heavy smokers 101 11.8 63 10.0 40 7.7 32 6.5
Methods
This study uses data on current smokers from 17 to 69 years of age during years 2000 to 2003. First, the demand function of the current smokers was established. Respondents who answered "everyday" or "some of the days" to the question how often you smoke were classified as "current smokers". Then, we used a random sampling of how they consumed and how much they paid for it between 2000 to 2003 to calculate cigarette price elasticity. We then analyzed differences in cigarette price elasticity in smokers categorized according to gender, age, education, income standard, and how much they smoked.Demand function Cigarette demand function was estimated by OLS and expressed by double logarithm function. The estimated demand function we used was: ln  Q ig  =  α 0  +  β 1  ln  P ig  +  γ 2  ln  I ig      (1) where lnQ ig  is i'th current smokers' logarithm representing monthly amount smokers consumed per person in group g. Current smokers were categorized according to age, gender, education, monthly income, and amount smoked. lnP ig  is i'th current smokers' logarithm representing cigarette price per pack (NT$) for smoking characteristics group g. lnI ig  is i'th current smokers' logarithm representing income per capita (NT$) for various categories of smokers in group g. The  α 0 ,  β 1 , and  γ 2  are parameters to be estimated. In order to measure how price change might affect cigarette consumption, the determination of price elasticity was particularly important. Price elasticity of demand for cigarettes is defined as the percent change in consumption resulting from a price increase. Cigarette price elasticity of demand  β 1  and income elasticity of demand  γ 2  can be derived from logarithmically differentiation (1) according to price and income.
Demand function
Cigarette demand function was estimated by OLS and expressed by double logarithm function. The estimated demand function we used was:ln  Q ig  =  α 0  +  β 1  ln  P ig  +  γ 2  ln  I ig      (1)QigαβPigγIigwherelnQ ig  is i'th current smokers' logarithm representing monthly amount smokers consumed per person in group g. Current smokers were categorized according to age, gender, education, monthly income, and amount smoked. lnP ig  is i'th current smokers' logarithm representing cigarette price per pack (NT$) for smoking characteristics group g. lnI ig  is i'th current smokers' logarithm representing income per capita (NT$) for various categories of smokers in group g.The  α 0 ,  β 1 , and  γ 2  are parameters to be estimated. In order to measure how price change might affect cigarette consumption, the determination of price elasticity was particularly important. Price elasticity of demand for cigarettes is defined as the percent change in consumption resulting from a price increase. Cigarette price elasticity of demand  β 1  and income elasticity of demand  γ 2  can be derived from logarithmically differentiation (1) according to price and income.αβγβγData collection Using an annual face-to-face survey on cigarette consumption from 2000 to 2003 by Taiwan National Health Research Institutes, we collected data on how many packs current smokers consumed, how much they paid for a pack of cigarettes, how much they earned per month and how much they spent on cigarettes per month. Current smokers were categorized into gender, age, education, income, and amount smoked. Calculations of cigarette price were based on the average retail price of the top 3 most consumed cigarettes, calculations of number of packs smoked per month were done by dividing the monthly cigarette consumption by the average retail price. Calculations of income were based on personal monthly income. Certain background characteristics are listed in Table  1 . More than 90% of the smokers were men; less than 10% women. The numbers of young smokers were rising at the time of the study. Young people between the ages of 17 and 24 years old made up 5.4% of the sample in 2000, while they made up 12.8% in 2003, a 1.4 percent increase. The number of elderly smokers above the age of 55 gradually declined from 15.5% in 2000 to 10.8% in 2003. People with higher educational backgrounds tended to smoke more. More than 60% of the current smokers had senior or junior high school educations between 2000 and 2002. Second only to smokers with senior high school degrees, the percentage of the smokers with college degree increased by 27.2% in 2003, accounting for almost 40% of all the smokers. Thirty-five to forty percent earned between NT $20,000 to NT $30,000 per month. Those who smoked less than one pack were defined as light smokers; 1~2 packs (2 packs excluded), medium smokers; and 2 packs and above, heavy smokers. The proportion of light smokers had gradually increased from 50% in 2000 to 60% in 2003, and the proportion of heavy smokers gradually decreased from 11.8% in 2000 to 6.5% in 2003, showing an overall tendency toward reducing consumption. Table 1 Background characteristics of the current smokers in Taiwan, 2000–2003 2000 2001 2002 2003 Characteristics No. % No. % No. % No. % Total 856 632 521 493 Gender  Male 789 92.2 599 94.8 496 95.0 460 93.3  Female 67 7.8 33 5.2 25 5.0 33 6.7 Age  17–24 46 5.4 35 5.5 41 7.9 63 12.8  25–34 179 20.9 133 21.0 94 18.0 101 20.5  35–44 299 34.9 222 35.1 190 36.5 177 35.9  45–54 199 23.2 149 23.6 122 23.4 99 20.1  55- 133 15.5 93 14.7 74 14.2 53 10.8 Education  College and above 168 19.6 128 20.3 107 20.5 134 27.2  Senior high school 317 37.0 245 38.8 195 37.4 196 39.8  Junior high school 216 25.2 153 24.2 136 26.1 98 19.9  Primary school or lower 155 18.1 106 16.8 83 15.9 65 13.2 Month income   No income 98 11.4 93 14.7 63 12.1 75 15.2   <NT $20,000 146 17.1 94 14.9 94 18.0 84 17.0  NT $ 20,000–39,999 335 39.1 237 37.5 192 36.9 174 35.3  NT $ 40,000–59,999 181 21.1 144 22.8 117 22.5 105 21.3  ≥ NT $ 60,000 96 11.2 64 10.1 55 10.6 55 11.2 Smoking degree   Light smokers 445 50.0 319 50.5 281 53.9 296 60.0  Medium smokers 310 36.2 250 39.6 200 38.4 165 33.5  Heavy smokers 101 11.8 63 10.0 40 7.7 32 6.5
Data collection
Using an annual face-to-face survey on cigarette consumption from 2000 to 2003 by Taiwan National Health Research Institutes, we collected data on how many packs current smokers consumed, how much they paid for a pack of cigarettes, how much they earned per month and how much they spent on cigarettes per month. Current smokers were categorized into gender, age, education, income, and amount smoked. Calculations of cigarette price were based on the average retail price of the top 3 most consumed cigarettes, calculations of number of packs smoked per month were done by dividing the monthly cigarette consumption by the average retail price. Calculations of income were based on personal monthly income.Certain background characteristics are listed in Table  1 . More than 90% of the smokers were men; less than 10% women. The numbers of young smokers were rising at the time of the study. Young people between the ages of 17 and 24 years old made up 5.4% of the sample in 2000, while they made up 12.8% in 2003, a 1.4 percent increase. The number of elderly smokers above the age of 55 gradually declined from 15.5% in 2000 to 10.8% in 2003. People with higher educational backgrounds tended to smoke more. More than 60% of the current smokers had senior or junior high school educations between 2000 and 2002. Second only to smokers with senior high school degrees, the percentage of the smokers with college degree increased by 27.2% in 2003, accounting for almost 40% of all the smokers. Thirty-five to forty percent earned between NT $20,000 to NT $30,000 per month. Those who smoked less than one pack were defined as light smokers; 1~2 packs (2 packs excluded), medium smokers; and 2 packs and above, heavy smokers. The proportion of light smokers had gradually increased from 50% in 2000 to 60% in 2003, and the proportion of heavy smokers gradually decreased from 11.8% in 2000 to 6.5% in 2003, showing an overall tendency toward reducing consumption.Background characteristics of the current smokers in Taiwan, 2000–2003TotalGenderAgeEducationMonth incomeSmoking degreeResults Cigarette consumption, retail price and personal monthly income were used in equation (1), the OLS method, to calculate cigarette price and income elasticities. The overall cigarette price elasticity was negative, less than one, indicating that cigarette consumption or demand in Taiwan was inelastic during the study period (Table  2 ). Taken into consideration that cigarette price elasticity is inelastic and that reduction of the cigarette consumption is done with a strategy of raising domestic cigarette price, we speculate that cigarette prices need to be even higher, to lower consumption enough to have a clear, strong impact in improved public health outcomes. While income elasticities were not statistically different from 2000 to 2002, they did reach a statistically significant level (5%) in 2003. At that time, estimated income elasticity was positive, indicating that cigarettes were normal goods. A positive value normally means that demand for normal goods would increase as incomes rise. But the value could vary greatly among normal goods. Interestingly, in our study, we found that as incomes were rose, income elasticity became low, indicating that income increases in 2003 only had a slight effect on cigarette consumption. Table 2 The estimated overall cigarette price and income elasticities of the current smokers, 2000–2003 a 2000 2001 2002 2003 Price elasticity -0.3134 (-2.894)* -0.3684 (-3.482)* -0.5274 (-3.143)* -0.3090 (-1.531) Income elasticity 0.0069 (0.708) 0.0042 (0.504) -0.0012 (-0.125) 0.0320 (2.916)* a. t ratios are shown in parentheses. * p < 0.05. After Taiwan's accession to WTO in 2002, Taiwan's first Tobacco Health and Welfare Tax added NT $5 the price of cigarettes, resulting in an increase in cigarette retail price from NT $35.2 in 2001 to NT $42.2 in 2002, about an NT $7 increase. In 2001, smokers 15 years old or older consumed an average 126.52 packs/person [ 14 ]. In 2002, the cigarette price elasticity became -0.5274, meaning that this price increase caused a reduction of cigarette consumption by 13.27 packs/person (10.5% per person) and a reduction of about 0.235 billion packs in the total consumption. Meanwhile, new cigarette consumption in 2002 was reduced to 2 billion packs for the population at and above the age of 15 in 2001. Provided there was a NT $16.8 tax on every pack of cigarettes, the tax revenue for the government would be 33.6 billion NT dollar. However, the tax has been in force for two years, and a significant reduction in consumption has been shown to date. Cigarette taxes accounted for 40% of the retail price in 2002. Although forty percent sounds high, this proportion is still rather low when, as mentioned earlier, comparing it with the 66% or more of the retail price going for cigarettes prices in high-income countries (with the notable exception of the United States)[ 9 ]. Consequently, cigarette prices in Taiwan are well below those of many high-income countries, who have seen significant reductions in cigarette consumption. Those successes certainly impose a pressure on the government to implement another tax increase in the existing Health and Welfare Tax. Inter-party negotiations at the Legislative Yuan resulted in changes to Tobacco and Liquor Tax Law which led to a NT $3 rise in the health tax levied on cigarettes, from NT$5 to NT$8 per pack. The cigarette industry is likely to pass the tax increase in the form of higher prices on to the consumer. A price increase of 3 NT per pack in cigarette would reflect a consumption reduction of 2.47 packs per capita, totaling 44.7 million packs, 2.2% per capita, in cigarette consumption. Cigarette consumption would be reduced to 2 billion packs (based on a population count of 2003), and the government tax revenue would be 33.46 billion, including the Health and Welfare Tax of 16 billion. We estimate that with a Health and Welfare Tax increase from 5 NT to 8 NT per pack, there would be a 6 billion NT increase in revenue from the Health and Welfare Tax. In 2000 and 2001, the cigarette price elasticities of the current smokers were -0.3134 and -0.3684, respectively. In 2002, it had reached its maximum of -0.5274, indicating that as cigarette prices increased, so did the price elasticity. Consumers responded to the higher prices by cutting consumption. Then in 2003, after Taiwan's accession to WTO, cigarette price elasticity then lowered to -0.309, indicating that the effect of a cigarette price hike can diminish over time. Two sets of previous data concerning the cigarette consumption, retail price and personal monthly income of the current smokers obtained during 2000–2001 and during 2002–2003, were made available to us. Using the OLS method and the rise of cigarette price in 2002 as the baseline, we computed the cigarette price and income elasticities for these two sets of data. Table  3  shows the differences in the overall cigarette price elasticity of the current smokers between before and after Taiwan's accession to WTO in 2002: before -0.4062 and after -0.3352. Our result clearly indicated that smokers were more responsive to the price after the cigarette price rose in 2002–2003. Yet, -0.4062 and -0.3352 also revealed that there was no big change in cigarette price elasticity before and after Taiwan's accession to WTO. The reason for this might be that the rise of average cigarette price was only NT $7 per pack. We speculate that a possible continuous and substantial rise in cigarette prices in the future might increase the overall price elasticity, which in turn could allow for a more effective use of the tax increases or price increases to control tobacco. Table 3 The estimated cigarette price and income elasticities of different types of current smokers during 2000–2001 and during 2002–2003 a 2000–2001 2002–2003 Characteristics Price elasticity Income elasticity Price elasticity Income elasticity Overall -0.3352 (-4.355)* 0.0055 (0.849) -0.4062 (-3.102)* 0.0174 (2.331)* Gender   Male -0.3107 (-4.036)* 0.0020 (0.291) -0.3930 (-2.935)* 0.0194 (2.450)*   Female -0.1223 (-0.312) -0.0206 (-0.820) -0.1406 (-0.251) -0.0476 (-1.903) Age   17–24 -0.4022 (-0.645) 0.0368 (1.151) -0.1057 (-0.144) 0.0420 (1.532)   25–34 -0.0528 (-0.274) -0.0038 (-0.227) 0.2300 (0.734) 0.0315 (1.822)   35–44 -0.1835 (-1.425) -0.0028 (-0.206) -0.2154 (-1.023) -0.0060 (-0.422)   45–54 -0.1540 (-1.087) 0.0048 (0.388) -0.4100 (-1.624) -0.0107 (-0.724)   55- -0.2453 (-1.073) -0.0080 (-0.608) -0.0475 (-0.118) 0.0008 (0.044) Education  College and above -0.1070 (-0.514) -0.0133 (-0.584) -0.7007 (-2.047)* 0.0919 (4.148)*  Senior high school -0.2772 (-2.273)* 0.0211 (1.825) -0.5369 (-2.703)* 0.0233 (2.069)*  Junior high school -0.5766 (-4.093)* 0.0275 (2.552)* 0.1789 (0.833) 0.0279 (2.058)*  Preliminary or lower 0.0560 (0.302) -0.0056 (-0.440) -0.0392 (-0.118) -0.0191 (-1.244) Month income  No income -0.5103 (-2.193)* -0.8363 (-2.014)*  <NT $20,000 -0.4570 (-2.373)* -0.7478 (-2.316)*  NT $ 20,000–39,999 -0.4805 (-3.953)* -0.2861 (-1.345)  NT $ 40,000–59,999 -0.1562 (-0.951) -0.2624 (-1.022)  ≥ NT $ 60,000 0.2341 (1.050) -0.1152 (-0.301) Smoking degree  Light smokers -0.1984 (-2.046)* 0.0087 (1.120) -0.5320 (-3.293)* 0.0172 (1.956)  Medium smokers -0.0228 (-0.914) -0.0005 (-0.198) -0.2600 (-5.068)* -0.0046 (-1.514)  Heavy smokers 0.2573 (1.973)* -0.0083 (-0.820) -0.0006 (-0.005) 0.0010 (0.137) a. t ratios are shown in parentheses. * p < 0.05. Cigarette price elasticity for the male smokers reached statistically significance (5%), which was higher than the price elasticity of the female smokers, indicating that men were more responsive to price elasticity than the women. The cigarette price elasticity of the male smokers in 2002–2003 was -0.393, which was higher than -0.3107 male smokers in 2000–2001. The income elasticity of male smokers in 2002–2003 was 0.0194, reaching statistical significance (5%). There was no statistical difference found in estimated cigarette price and income elasticity of smokers among the different age sub-groups, though, according to some reports in foreign countries, teenagers are more sensitive changes to cigarette prices than adults [ 15 - 17 ]. Education level seemed to make a difference. The price elasticity smokers with junior high school educations was -0.5766 in 2000–2001, which was higher than that of senior high school level smokers, -0.2772. In 2002-2003, the price elasticity of college level smokers was -0.7007, which was higher than that of the smokers of senior high school level, -0.5369. Therefore, between 2000 and 2001, the more educated group had a larger price elasticity, though the less educated group had the higher coefficient in 2002–2003. Our findings cover two time spans and are different from those reported by foreign researchers who have found that consumers at lower education levels respond stronger to the change of cigarette price [ 18 ]. In our study, those with no income had the greatest cigarette price elasticity, -0.5103 in 2000–2001 and -0.8363 in 2002–2003. Those with no income were more sensitive to the price rise than those with income. Light smokers had the highest cigarette price elasticity, -0.1984 in 2000–2001 and -0.532 in 2002–2003. Heavy smokers had a price elasticity of 0.2573 in 2000–2001, indicating that with the rise of cigarette price, these smokers increased their consumption of tobacco.
Results
Cigarette consumption, retail price and personal monthly income were used in equation (1), the OLS method, to calculate cigarette price and income elasticities. The overall cigarette price elasticity was negative, less than one, indicating that cigarette consumption or demand in Taiwan was inelastic during the study period (Table  2 ). Taken into consideration that cigarette price elasticity is inelastic and that reduction of the cigarette consumption is done with a strategy of raising domestic cigarette price, we speculate that cigarette prices need to be even higher, to lower consumption enough to have a clear, strong impact in improved public health outcomes. While income elasticities were not statistically different from 2000 to 2002, they did reach a statistically significant level (5%) in 2003. At that time, estimated income elasticity was positive, indicating that cigarettes were normal goods. A positive value normally means that demand for normal goods would increase as incomes rise. But the value could vary greatly among normal goods. Interestingly, in our study, we found that as incomes were rose, income elasticity became low, indicating that income increases in 2003 only had a slight effect on cigarette consumption.The estimated overall cigarette price and income elasticities of the current smokers, 2000–2003 aa. t ratios are shown in parentheses.* p < 0.05.After Taiwan's accession to WTO in 2002, Taiwan's first Tobacco Health and Welfare Tax added NT $5 the price of cigarettes, resulting in an increase in cigarette retail price from NT $35.2 in 2001 to NT $42.2 in 2002, about an NT $7 increase. In 2001, smokers 15 years old or older consumed an average 126.52 packs/person [ 14 ]. In 2002, the cigarette price elasticity became -0.5274, meaning that this price increase caused a reduction of cigarette consumption by 13.27 packs/person (10.5% per person) and a reduction of about 0.235 billion packs in the total consumption. Meanwhile, new cigarette consumption in 2002 was reduced to 2 billion packs for the population at and above the age of 15 in 2001. Provided there was a NT $16.8 tax on every pack of cigarettes, the tax revenue for the government would be 33.6 billion NT dollar.However, the tax has been in force for two years, and a significant reduction in consumption has been shown to date. Cigarette taxes accounted for 40% of the retail price in 2002. Although forty percent sounds high, this proportion is still rather low when, as mentioned earlier, comparing it with the 66% or more of the retail price going for cigarettes prices in high-income countries (with the notable exception of the United States)[ 9 ]. Consequently, cigarette prices in Taiwan are well below those of many high-income countries, who have seen significant reductions in cigarette consumption. Those successes certainly impose a pressure on the government to implement another tax increase in the existing Health and Welfare Tax.Inter-party negotiations at the Legislative Yuan resulted in changes to Tobacco and Liquor Tax Law which led to a NT $3 rise in the health tax levied on cigarettes, from NT$5 to NT$8 per pack. The cigarette industry is likely to pass the tax increase in the form of higher prices on to the consumer. A price increase of 3 NT per pack in cigarette would reflect a consumption reduction of 2.47 packs per capita, totaling 44.7 million packs, 2.2% per capita, in cigarette consumption. Cigarette consumption would be reduced to 2 billion packs (based on a population count of 2003), and the government tax revenue would be 33.46 billion, including the Health and Welfare Tax of 16 billion. We estimate that with a Health and Welfare Tax increase from 5 NT to 8 NT per pack, there would be a 6 billion NT increase in revenue from the Health and Welfare Tax.In 2000 and 2001, the cigarette price elasticities of the current smokers were -0.3134 and -0.3684, respectively. In 2002, it had reached its maximum of -0.5274, indicating that as cigarette prices increased, so did the price elasticity. Consumers responded to the higher prices by cutting consumption. Then in 2003, after Taiwan's accession to WTO, cigarette price elasticity then lowered to -0.309, indicating that the effect of a cigarette price hike can diminish over time.Two sets of previous data concerning the cigarette consumption, retail price and personal monthly income of the current smokers obtained during 2000–2001 and during 2002–2003, were made available to us. Using the OLS method and the rise of cigarette price in 2002 as the baseline, we computed the cigarette price and income elasticities for these two sets of data. Table  3  shows the differences in the overall cigarette price elasticity of the current smokers between before and after Taiwan's accession to WTO in 2002: before -0.4062 and after -0.3352. Our result clearly indicated that smokers were more responsive to the price after the cigarette price rose in 2002–2003. Yet, -0.4062 and -0.3352 also revealed that there was no big change in cigarette price elasticity before and after Taiwan's accession to WTO. The reason for this might be that the rise of average cigarette price was only NT $7 per pack. We speculate that a possible continuous and substantial rise in cigarette prices in the future might increase the overall price elasticity, which in turn could allow for a more effective use of the tax increases or price increases to control tobacco.The estimated cigarette price and income elasticities of different types of current smokers during 2000–2001 and during 2002–2003 aOverallGenderAgeEducationMonth incomeSmoking degreea. t ratios are shown in parentheses.* p < 0.05.Cigarette price elasticity for the male smokers reached statistically significance (5%), which was higher than the price elasticity of the female smokers, indicating that men were more responsive to price elasticity than the women. The cigarette price elasticity of the male smokers in 2002–2003 was -0.393, which was higher than -0.3107 male smokers in 2000–2001. The income elasticity of male smokers in 2002–2003 was 0.0194, reaching statistical significance (5%). There was no statistical difference found in estimated cigarette price and income elasticity of smokers among the different age sub-groups, though, according to some reports in foreign countries, teenagers are more sensitive changes to cigarette prices than adults [ 15 - 17 ].Education level seemed to make a difference. The price elasticity smokers with junior high school educations was -0.5766 in 2000–2001, which was higher than that of senior high school level smokers, -0.2772. In 2002-2003, the price elasticity of college level smokers was -0.7007, which was higher than that of the smokers of senior high school level, -0.5369. Therefore, between 2000 and 2001, the more educated group had a larger price elasticity, though the less educated group had the higher coefficient in 2002–2003. Our findings cover two time spans and are different from those reported by foreign researchers who have found that consumers at lower education levels respond stronger to the change of cigarette price [ 18 ]. In our study, those with no income had the greatest cigarette price elasticity, -0.5103 in 2000–2001 and -0.8363 in 2002–2003. Those with no income were more sensitive to the price rise than those with income. Light smokers had the highest cigarette price elasticity, -0.1984 in 2000–2001 and -0.532 in 2002–2003. Heavy smokers had a price elasticity of 0.2573 in 2000–2001, indicating that with the rise of cigarette price, these smokers increased their consumption of tobacco.Conclusions In this study, we evaluate the effect of a new tax on the consumption of tobacco by calculating the cigarette price elasticities of various kinds of smokers and comparing those values with their reactions to an increase cigarette, and then using knowledge gained from that study, we assess the possible effect of another increase on consumption. We found that the new tax scheme implemented after Taiwan joined the WTO reduced cigarette consumption by 13.27 packs/person (10.5%). We estimated that an additional NT $3 increase in Taiwan's Health and Welfare Tax would reduce cigarette consumption here by 2.47 packs/person (2.2%). In this study, cigarette price elasticity was less than one, meaning that in addition to reducing cigarette consumption, an additional tax would also generate additional tax revenues. Continuing price increases should reduce cigarette consumption significantly. Provided that the tax increases are proportionately larger than the resulting reduction in cigarette consumption, cigarette tax revenues will increase and can be used to reduce current National Health Insurance deficits and possibly reduce the damage and death caused by smoking related diseases. Based on estimated cigarette price elasticities for various kinds of current smokers, we found that male smokers without income and light smokers were more sensitive to changes in cigarette prices. Teenagers (17 – 24 years old), however, were not found to be significantly influenced by the change in cigarette price, which means it will take more than just tax increases to decrease consumption among our youth. Schools will need to commit to preventive education by inculcating the students with the knowledge of tobacco hazards. Only through early preventive education starting from their childhood can we expect to see significant reduction in cigarette consumption. Finally, the R-squared statistics of the each empirical estimation was below 0.1 for probably sake of to calculate elasticity and exclude variables like advertisement. Future research should also attempt to include these factors with cigarette demand function.
Conclusions
In this study, we evaluate the effect of a new tax on the consumption of tobacco by calculating the cigarette price elasticities of various kinds of smokers and comparing those values with their reactions to an increase cigarette, and then using knowledge gained from that study, we assess the possible effect of another increase on consumption. We found that the new tax scheme implemented after Taiwan joined the WTO reduced cigarette consumption by 13.27 packs/person (10.5%). We estimated that an additional NT $3 increase in Taiwan's Health and Welfare Tax would reduce cigarette consumption here by 2.47 packs/person (2.2%).In this study, cigarette price elasticity was less than one, meaning that in addition to reducing cigarette consumption, an additional tax would also generate additional tax revenues. Continuing price increases should reduce cigarette consumption significantly. Provided that the tax increases are proportionately larger than the resulting reduction in cigarette consumption, cigarette tax revenues will increase and can be used to reduce current National Health Insurance deficits and possibly reduce the damage and death caused by smoking related diseases.Based on estimated cigarette price elasticities for various kinds of current smokers, we found that male smokers without income and light smokers were more sensitive to changes in cigarette prices. Teenagers (17 – 24 years old), however, were not found to be significantly influenced by the change in cigarette price, which means it will take more than just tax increases to decrease consumption among our youth. Schools will need to commit to preventive education by inculcating the students with the knowledge of tobacco hazards. Only through early preventive education starting from their childhood can we expect to see significant reduction in cigarette consumption.Finally, the R-squared statistics of the each empirical estimation was below 0.1 for probably sake of to calculate elasticity and exclude variables like advertisement. Future research should also attempt to include these factors with cigarette demand function.Competing interests The author(s) declare that they have no competing interests.
Competing interests
The author(s) declare that they have no competing interests.Authors' contributions JML performed physical measurements, collected data, and drafted the manuscript. TCH reviewed the manuscript. CYY and SHC carried out the statistical analysis and participated in data collection. All authors read and approved the final manuscript.
Authors' contributions
JML performed physical measurements, collected data, and drafted the manuscript. TCH reviewed the manuscript. CYY and SHC carried out the statistical analysis and participated in data collection. All authors read and approved the final manuscript.Pre-publication history The pre-publication history for this paper can be accessed here:
Pre-publication history
The pre-publication history for this paper can be accessed here:


Our sense of taste begins with taste buds and ends in the brain. Researchers are beginning to unravel the mechanisms and connections that lie in between

The ability to taste food is a life-and-death matter. Failure to recognise food with a high enough caloric content could mean a slow death from malnutrition. Failure to detect a poison could result in near-instant expiration. And now, as researchers begin to understand some of the nuts and bolts of taste perception, it seems that the sense of taste may also have more subtle effects on health.The Basics of Taste At the front line of the taste sensory system are the taste buds—onion-shaped structures on the tongue and elsewhere in the mouth ( Figure 1 ). Up to 100 taste receptor cells—epithelial cells with some neuronal properties—are arranged in each taste bud. In the tongue, the taste buds are innervated by the chorda tympani (a branch of the facial nerve) and the glossopharyngeal nerve. These nerves carry the taste messages to the brain. Figure 1 A Taste Bud in a Mouse This taste bud was taken from a transgenic mouse in which the marker green fluorescent protein is being driven by the T1R3 promoter; 20%–30% of the cells in the taste bud are expressing T1R3. (Photograph courtesy of Sami Damak, Mount Sinai School of Medicine, New York, New York, United States.) Taste is the sense by which the chemical qualities of food in the mouth are distinguished by the brain, based on information provided by the taste buds. Quality or ‘basic taste’, explains Bernd Lindemann, now retired but an active taste researcher in Germany for many years, is a psychophysical term. Large numbers of people describe different tastants and then statistical analyses are used to define the important tastes. ‘The number of taste qualities has varied over the years’, says Lindemann. ‘We are now settling at around five, though I would not be surprised if some additional qualities pop up’. The five qualities that Lindemann refers to are salty, sour, bitter, sweet, and umami, the last being the Japanese term for a savoury sensation. Salty and sour detection is needed to control salt and acid balance. Bitter detection warns of foods containing poisons—many of the poisonous compounds produced by plants for defence are bitter. The quality sweet provides a guide to calorie-rich foods. And umami (the taste of the amino acid glutamate) may flag up protein-rich foods. Our sense of taste has a simple goal, explains Lindemann: ‘Food is already in the mouth. We just have to decide whether to swallow or spit it out. It's an extremely important decision, but it can be made based on a few taste qualities’.
The Basics of Taste
At the front line of the taste sensory system are the taste buds—onion-shaped structures on the tongue and elsewhere in the mouth ( Figure 1 ). Up to 100 taste receptor cells—epithelial cells with some neuronal properties—are arranged in each taste bud. In the tongue, the taste buds are innervated by the chorda tympani (a branch of the facial nerve) and the glossopharyngeal nerve. These nerves carry the taste messages to the brain.Taste is the sense by which the chemical qualities of food in the mouth are distinguished by the brain, based on information provided by the taste buds. Quality or ‘basic taste’, explains Bernd Lindemann, now retired but an active taste researcher in Germany for many years, is a psychophysical term. Large numbers of people describe different tastants and then statistical analyses are used to define the important tastes. ‘The number of taste qualities has varied over the years’, says Lindemann. ‘We are now settling at around five, though I would not be surprised if some additional qualities pop up’.The five qualities that Lindemann refers to are salty, sour, bitter, sweet, and umami, the last being the Japanese term for a savoury sensation. Salty and sour detection is needed to control salt and acid balance. Bitter detection warns of foods containing poisons—many of the poisonous compounds produced by plants for defence are bitter. The quality sweet provides a guide to calorie-rich foods. And umami (the taste of the amino acid glutamate) may flag up protein-rich foods. Our sense of taste has a simple goal, explains Lindemann: ‘Food is already in the mouth. We just have to decide whether to swallow or spit it out. It's an extremely important decision, but it can be made based on a few taste qualities’.From Physiology to Molecular Biology Taste has been actively researched for many decades. During the 20th century, electrophysiologists and other researchers worked hard to understand this seemingly simple sense system. Then, in 1991, the first olfactory receptors were described. These proteins, which are exposed on the surface of cells in the nose, bind to volatile chemicals and allow us to detect smells. This landmark discovery, in part, encouraged many established taste researchers to investigate the molecular aspects of taste. The olfaction results also enticed researchers from other disciplines into the taste field, including collaborators Charles Zuker (University of California, San Diego [UCSD], La Jolla, California, United States) and Nick Ryba (National Institute of Dental and Craniofacial Research [NIDCR], Bethesda, Maryland, United States). About six years ago, explains Zuker, who previously worked on other sensory systems in flies, ‘there was a disconnect between our understanding of sensations in the case of photoreception, mechanoreception, touch, and so on and what we knew about taste’. There was evidence, says Ryba, that a class of protein receptors called G-protein-coupled receptors (GPCRs) were involved in sweet and bitter taste, ‘but the receptors weren't known, so we started to look for them …. These molecules are intrinsically interesting, but more importantly, they provide tools with which we can dissect out how taste works’.
From Physiology to Molecular Biology
Taste has been actively researched for many decades. During the 20th century, electrophysiologists and other researchers worked hard to understand this seemingly simple sense system. Then, in 1991, the first olfactory receptors were described. These proteins, which are exposed on the surface of cells in the nose, bind to volatile chemicals and allow us to detect smells. This landmark discovery, in part, encouraged many established taste researchers to investigate the molecular aspects of taste.The olfaction results also enticed researchers from other disciplines into the taste field, including collaborators Charles Zuker (University of California, San Diego [UCSD], La Jolla, California, United States) and Nick Ryba (National Institute of Dental and Craniofacial Research [NIDCR], Bethesda, Maryland, United States). About six years ago, explains Zuker, who previously worked on other sensory systems in flies, ‘there was a disconnect between our understanding of sensations in the case of photoreception, mechanoreception, touch, and so on and what we knew about taste’. There was evidence, says Ryba, that a class of protein receptors called G-protein-coupled receptors (GPCRs) were involved in sweet and bitter taste, ‘but the receptors weren't known, so we started to look for them …. These molecules are intrinsically interesting, but more importantly, they provide tools with which we can dissect out how taste works’.Bitter, Sweet, and Umami Receptors The bitter receptors fell first to the onslaught of the UCSD–NIDCR team and other molecular biologists. In 1999, the ability to taste propylthiouracil, a bitter tasting compound, had been linked to a locus on human Chromosome 5p15. Reasoning that this variation might be due to alterations in the coding sequence for a bitter receptor, the UCSD–NIDCR researchers used the draft of the human genome to search for sequences that resembled GPCRs on Chromosome 5p15. ‘That was how we found T2R1, the first bitter receptor, and, subsequently, a whole family of T2Rs’, says Zuker.
 Researchers want to know: how is taste coded?
 All these receptors, says Zuker, are coexpressed in bitter taste receptor cells, a result that contradicts other research showing that different bitter-responsive cells react to different bitter molecules. ‘To me’, says Zuker, ‘it makes sense that all the bitter receptors would be expressed in each bitter taste cell. We just need to know if something is bitter to avoid death’, not the exact identity of the bitter tastant. The sweet receptor story started in 1999 with the identification of two putative mammalian taste receptors, GPCRs now known as T1R1 and T1R2. In early 2001, four groups reported an association between the mouse  Sac  locus, which determines the ability of mice to detect saccharin, and T1R3, a third member of the T1R family. The UCSD–NIDCR team subsequently showed that the T1R2 and T1R3 heterodimer (a complex of one T1R2 and one T1R3 molecule) forms a broadly tuned sweet receptor, responsive to natural sugars and artificial sweeteners, and that a homodimer of two T1R3 molecules forms a low-affinity sugar receptor that responds to high concentrations of natural sugars only. All sweet detection, concludes Zuker, is via the T1R2 and T1R3 receptors. And umami? A truncated glutamate receptor was identified as an umami receptor by researchers at the University of Miami (Florida, United States) School of Medicine in 2000. Zuker, however, believes that the one and only umami receptor is a heterodimer of T1R1 and T1R3. In October 2003, Zuker and his coworkers reported that mice in which either T1R1 or T1R3 has been knocked out show no preference for monosodium glutamate (MSG), an umami tastant. However, other researchers reported in August 2003 that T1R3 knockouts retain some preference for MSG. ‘We believe this is due either to the truncated glutamate receptor or another unknown receptor’, says lead author Sami Damak (Mount Sinai School of Medicine, New York, New York, United States). Damak says he does not know why the two sets of T1R3 knockout mice behaved differently, but the UCSD–NIDCR researchers suggest that the residual response to MSG seen by Damak et al. is a response to the sodium content of MSG. Damak is not alone, however, in thinking there may be more than one umami receptor (and additional sweet receptors). Commenting on these recent discoveries, taste expert Linda Bartoshuk (Yale University School of Medicine, New Haven, Connecticut, United States) says that ‘it is lovely to see all these details, especially as they confirm what we already believed conceptually’. For example, she says, it is no surprise that there are many bitter receptors but probably only one sweet receptor. ‘There are so many poisons and it makes perfect sense to have lots of receptors feeding into a common transduction pathway. Sweet is a different problem. In nature, there are many molecules with structures similar to sugar that we must not eat because we cannot metabolise them. So I would have predicted one or at most a few highly specific sweet receptors’.
Bitter, Sweet, and Umami Receptors
The bitter receptors fell first to the onslaught of the UCSD–NIDCR team and other molecular biologists. In 1999, the ability to taste propylthiouracil, a bitter tasting compound, had been linked to a locus on human Chromosome 5p15. Reasoning that this variation might be due to alterations in the coding sequence for a bitter receptor, the UCSD–NIDCR researchers used the draft of the human genome to search for sequences that resembled GPCRs on Chromosome 5p15. ‘That was how we found T2R1, the first bitter receptor, and, subsequently, a whole family of T2Rs’, says Zuker.Researchers want to know: how is taste coded?Researchers want to know: how is taste coded?All these receptors, says Zuker, are coexpressed in bitter taste receptor cells, a result that contradicts other research showing that different bitter-responsive cells react to different bitter molecules. ‘To me’, says Zuker, ‘it makes sense that all the bitter receptors would be expressed in each bitter taste cell. We just need to know if something is bitter to avoid death’, not the exact identity of the bitter tastant.The sweet receptor story started in 1999 with the identification of two putative mammalian taste receptors, GPCRs now known as T1R1 and T1R2. In early 2001, four groups reported an association between the mouse  Sac  locus, which determines the ability of mice to detect saccharin, and T1R3, a third member of the T1R family. The UCSD–NIDCR team subsequently showed that the T1R2 and T1R3 heterodimer (a complex of one T1R2 and one T1R3 molecule) forms a broadly tuned sweet receptor, responsive to natural sugars and artificial sweeteners, and that a homodimer of two T1R3 molecules forms a low-affinity sugar receptor that responds to high concentrations of natural sugars only. All sweet detection, concludes Zuker, is via the T1R2 and T1R3 receptors.SacAnd umami? A truncated glutamate receptor was identified as an umami receptor by researchers at the University of Miami (Florida, United States) School of Medicine in 2000. Zuker, however, believes that the one and only umami receptor is a heterodimer of T1R1 and T1R3. In October 2003, Zuker and his coworkers reported that mice in which either T1R1 or T1R3 has been knocked out show no preference for monosodium glutamate (MSG), an umami tastant. However, other researchers reported in August 2003 that T1R3 knockouts retain some preference for MSG. ‘We believe this is due either to the truncated glutamate receptor or another unknown receptor’, says lead author Sami Damak (Mount Sinai School of Medicine, New York, New York, United States). Damak says he does not know why the two sets of T1R3 knockout mice behaved differently, but the UCSD–NIDCR researchers suggest that the residual response to MSG seen by Damak et al. is a response to the sodium content of MSG. Damak is not alone, however, in thinking there may be more than one umami receptor (and additional sweet receptors).Commenting on these recent discoveries, taste expert Linda Bartoshuk (Yale University School of Medicine, New Haven, Connecticut, United States) says that ‘it is lovely to see all these details, especially as they confirm what we already believed conceptually’. For example, she says, it is no surprise that there are many bitter receptors but probably only one sweet receptor. ‘There are so many poisons and it makes perfect sense to have lots of receptors feeding into a common transduction pathway. Sweet is a different problem. In nature, there are many molecules with structures similar to sugar that we must not eat because we cannot metabolise them. So I would have predicted one or at most a few highly specific sweet receptors’.What about Salty and Sour Receptors? The salty and sour receptors may be very different from the GPCRs involved in bitter, sweet, and umami perception, which bind complex molecules on the outside of the cell and transmit a signal into the cell. For salty and sour perception, the taste cell only needs to detect simple ions. One way to do this may be to use ion channels—proteins that form a channel through which specific inorganic ions can diffuse. Changes in cellular ion concentrations could then be detected and transmitted to the nervous system. Physiologist John DeSimone (Virginia Commonwealth University, Richmond, Virginia, United States) says there are at least two ion channel receptors for salt in rodent taste receptor cells. The first of these is the epithelial sodium channel, a widely expressed channel that can be blocked specifically with the drug amiloride. In rats, says DeSimone, only 75% of the nerve response to salt can be blocked by amiloride, so there is probably a second receptor. This, he says, seems to be a generalist salt receptor—the amiloride-sensitive channel only responds to sodium chloride—and may be the more important receptor in people. Sour tastants are acids, often found in spoiled or unripe food. DeSimone's current idea is that strong acids enter taste cells through a proton channel (probably a known channel present on other cell types) while weak acids, like acetic acid (vinegar), enter as neutral molecules and then dissociate to lower intracellular pH. DeSimone believes that he has identified the proton channel involved in sour taste as well as an ion channel that could be the second salt receptor, and he plans to do knockout experiments on both. If these channels are essential elsewhere in the body, as DeSimone suspects, to avoid lethality he will need to construct conditional knockouts in which the channel is lost only in the taste receptor cells. Zuker, meanwhile, is not convinced that the current ion channel candidates for salt and sour perception are correct. And, he says, GPCRs could also be involved in these modalities. ‘There is a precedent for that’, he claims, noting that extracellular calcium is sensed by a GPCR.
What about Salty and Sour Receptors?
The salty and sour receptors may be very different from the GPCRs involved in bitter, sweet, and umami perception, which bind complex molecules on the outside of the cell and transmit a signal into the cell. For salty and sour perception, the taste cell only needs to detect simple ions. One way to do this may be to use ion channels—proteins that form a channel through which specific inorganic ions can diffuse. Changes in cellular ion concentrations could then be detected and transmitted to the nervous system.Physiologist John DeSimone (Virginia Commonwealth University, Richmond, Virginia, United States) says there are at least two ion channel receptors for salt in rodent taste receptor cells. The first of these is the epithelial sodium channel, a widely expressed channel that can be blocked specifically with the drug amiloride. In rats, says DeSimone, only 75% of the nerve response to salt can be blocked by amiloride, so there is probably a second receptor. This, he says, seems to be a generalist salt receptor—the amiloride-sensitive channel only responds to sodium chloride—and may be the more important receptor in people.Sour tastants are acids, often found in spoiled or unripe food. DeSimone's current idea is that strong acids enter taste cells through a proton channel (probably a known channel present on other cell types) while weak acids, like acetic acid (vinegar), enter as neutral molecules and then dissociate to lower intracellular pH. DeSimone believes that he has identified the proton channel involved in sour taste as well as an ion channel that could be the second salt receptor, and he plans to do knockout experiments on both. If these channels are essential elsewhere in the body, as DeSimone suspects, to avoid lethality he will need to construct conditional knockouts in which the channel is lost only in the taste receptor cells.Zuker, meanwhile, is not convinced that the current ion channel candidates for salt and sour perception are correct. And, he says, GPCRs could also be involved in these modalities. ‘There is a precedent for that’, he claims, noting that extracellular calcium is sensed by a GPCR.Taste-Coding With many taste receptors now identified, researchers are turning to a long-standing question in taste perception: how is taste coded? When we eat, our tongue is bombarded with tastants. How is their detection and transduction of information organised so that the appropriate response is elicited? Taste physiologist Sue Kinnamon (Colorado State University, Fort Collins, Colorado, United States) explains the two theories of taste-coding. In the ‘labelled-line’ model, sweet-sensitive cells, for example, are hooked up to sweet-sensitive nerve fibres that go to the brain and code sweet. If you stimulate that pathway, says Kinnamon, ‘you should elicit the appropriate behavioural response without any input from other cell types’. In the ‘cross-fibre’ model, the pattern of activity over many receptors codes taste. This model predicts that taste receptor cells are broadly tuned, responding to many tastants. Support for this theory, says Kinnamon, comes from electrical recordings from receptor cells and from nerves innervating the taste buds that show that one cell can respond to more than one taste quality. Zuker and Ryba's recent work strongly suggests that taste-coding for bitter, sweet, and umami fits the labelled-line model in the periphery of the taste system. Their expression data show that receptors for these qualities are expressed in distinct populations of taste cells. In addition, in early 2003, they reported that, as in other sensory systems, a single signalling pathway involving the ion channel TRPM5 and PLCβ2, a phospholipase that produces a TRPM5 activator, lies downstream of the bitter, sweet, and umami receptors. When the UCSD–NIDCR researchers took PLCβ2 knockout mice, which did not respond to bitter, sweet, or umami, and engineered them so that PLCβ2 was only expressed in bitter receptor-expressing cells, only the ability to respond to bitter tastants was regained. These data, says Zuker, support the labelled-line model. The latest data supporting the labelled-line model came last October when Zuker and colleagues described mice in which a non-taste receptor—a modified κ-opioid receptor that can only be activated by a synthetic ligand—was expressed only in cells expressing T1R2, sweet-responsive cells. The mice were attracted to the synthetic ligand, which they normally ignore, indicating that dedicated pathways mediate attractive behaviours. The researchers plan similar experiments to see whether the same is true for aversive behaviours. Even with all these molecular data, the cross-fibre model of taste-coding still has its supporters—just how many depends on whom one talks to. Both Damak and Kinnamon, for example, believe that there is at least some involvement of cross-fibre patterning even in the taste receptor cells. But, says neurobiologist and olfaction expert Lawrence C. Katz (Duke University, Durham, North Carolina, United States), ‘the onus is now on people who believe otherwise [than the labelled-line model] to provide compelling proof for the cross-fibre theory because now, at least at the periphery, the evidence is compelling for a labelled line for bitter, sweet, and umami’. Bartoshuk also says the debate is decided in favour of the labelled-line model in the periphery. The crossfibre model is an interesting historical footnote, she comments. Whether this putative link between taste perception and health can be confirmed and whether it will be possible to manipulate food preferences to improve health remain to be seen. However, it seems certain that, as in the past five years, the next five years will see large advances in our knowledge of many aspects of taste, a fascinating and important sensory system.
Taste-Coding
With many taste receptors now identified, researchers are turning to a long-standing question in taste perception: how is taste coded? When we eat, our tongue is bombarded with tastants. How is their detection and transduction of information organised so that the appropriate response is elicited? Taste physiologist Sue Kinnamon (Colorado State University, Fort Collins, Colorado, United States) explains the two theories of taste-coding. In the ‘labelled-line’ model, sweet-sensitive cells, for example, are hooked up to sweet-sensitive nerve fibres that go to the brain and code sweet. If you stimulate that pathway, says Kinnamon, ‘you should elicit the appropriate behavioural response without any input from other cell types’. In the ‘cross-fibre’ model, the pattern of activity over many receptors codes taste. This model predicts that taste receptor cells are broadly tuned, responding to many tastants. Support for this theory, says Kinnamon, comes from electrical recordings from receptor cells and from nerves innervating the taste buds that show that one cell can respond to more than one taste quality.Zuker and Ryba's recent work strongly suggests that taste-coding for bitter, sweet, and umami fits the labelled-line model in the periphery of the taste system. Their expression data show that receptors for these qualities are expressed in distinct populations of taste cells. In addition, in early 2003, they reported that, as in other sensory systems, a single signalling pathway involving the ion channel TRPM5 and PLCβ2, a phospholipase that produces a TRPM5 activator, lies downstream of the bitter, sweet, and umami receptors. When the UCSD–NIDCR researchers took PLCβ2 knockout mice, which did not respond to bitter, sweet, or umami, and engineered them so that PLCβ2 was only expressed in bitter receptor-expressing cells, only the ability to respond to bitter tastants was regained. These data, says Zuker, support the labelled-line model.The latest data supporting the labelled-line model came last October when Zuker and colleagues described mice in which a non-taste receptor—a modified κ-opioid receptor that can only be activated by a synthetic ligand—was expressed only in cells expressing T1R2, sweet-responsive cells. The mice were attracted to the synthetic ligand, which they normally ignore, indicating that dedicated pathways mediate attractive behaviours. The researchers plan similar experiments to see whether the same is true for aversive behaviours.Even with all these molecular data, the cross-fibre model of taste-coding still has its supporters—just how many depends on whom one talks to. Both Damak and Kinnamon, for example, believe that there is at least some involvement of cross-fibre patterning even in the taste receptor cells. But, says neurobiologist and olfaction expert Lawrence C. Katz (Duke University, Durham, North Carolina, United States), ‘the onus is now on people who believe otherwise [than the labelled-line model] to provide compelling proof for the cross-fibre theory because now, at least at the periphery, the evidence is compelling for a labelled line for bitter, sweet, and umami’. Bartoshuk also says the debate is decided in favour of the labelled-line model in the periphery. The crossfibre model is an interesting historical footnote, she comments.Whether this putative link between taste perception and health can be confirmed and whether it will be possible to manipulate food preferences to improve health remain to be seen. However, it seems certain that, as in the past five years, the next five years will see large advances in our knowledge of many aspects of taste, a fascinating and important sensory system.What Next—and Why Study Taste Anyway? The periphery of the taste sensory system has yielded many of its secrets, but relatively little is known about the transduction pathways in taste, how taste cells talk to the nervous system, or about events further downstream in the brain. How are signals from taste receptors integrated with those from olfactory receptors to form a representation of complex food flavours, for example? With their expanding molecular toolbox, researchers can now delve deeper into these aspects of taste perception. This may tell us not only about taste but about how the nervous system in general is put together, says Ryba. But understanding taste is not just an academic exercise. It has practical uses too. DeSimone suggests that by understanding salt receptors, it may be possible to design artificial ligands to help people lower their salt intake. As Kinnamon succinctly puts it, ‘Can you imagine eating potato chips and not having the salty component?’ An artificial salt receptor ligand could make salt-free foods a palatable option for people with high blood pressure. Lindemann also sees a great future in artificial ligands for taste receptors. The sense of taste is partly lost in elderly people, he says, so better tastants—effectively ‘chemical spectacles’—might give them back their pleasure of eating and thereby improve their quality of life. Finally, some aspects of taste may be inextricably tied up with general health, says Bartoshuk. Many people who can taste propylthiouracil are also ‘supertasters’—they have more fungiform papillae, structures containing taste buds, on their tongues than non-tasters ( Figure 2 ). Supertasters find vegetables bitter—particularly brassicas, like Brussel sprouts—so they tend to eat fewer vegetables as part of their regular diet than non-tasters. ‘Being a supertaster affects your taste preferences, your diet, and ultimately your health’, claims Bartoshuk. Figure 2 Non-Taster or Supertaster? (A) Top surface of the tongue of a non-taster. (B) Tongue of a supertaster. The small circles are fungiform papillae, each of which contains about six taste buds.
What Next—and Why Study Taste Anyway?
The periphery of the taste sensory system has yielded many of its secrets, but relatively little is known about the transduction pathways in taste, how taste cells talk to the nervous system, or about events further downstream in the brain. How are signals from taste receptors integrated with those from olfactory receptors to form a representation of complex food flavours, for example? With their expanding molecular toolbox, researchers can now delve deeper into these aspects of taste perception. This may tell us not only about taste but about how the nervous system in general is put together, says Ryba.But understanding taste is not just an academic exercise. It has practical uses too. DeSimone suggests that by understanding salt receptors, it may be possible to design artificial ligands to help people lower their salt intake. As Kinnamon succinctly puts it, ‘Can you imagine eating potato chips and not having the salty component?’ An artificial salt receptor ligand could make salt-free foods a palatable option for people with high blood pressure. Lindemann also sees a great future in artificial ligands for taste receptors. The sense of taste is partly lost in elderly people, he says, so better tastants—effectively ‘chemical spectacles’—might give them back their pleasure of eating and thereby improve their quality of life.Finally, some aspects of taste may be inextricably tied up with general health, says Bartoshuk. Many people who can taste propylthiouracil are also ‘supertasters’—they have more fungiform papillae, structures containing taste buds, on their tongues than non-tasters ( Figure 2 ). Supertasters find vegetables bitter—particularly brassicas, like Brussel sprouts—so they tend to eat fewer vegetables as part of their regular diet than non-tasters. ‘Being a supertaster affects your taste preferences, your diet, and ultimately your health’, claims Bartoshuk.