Association of serum 25-hydroxyvitamin D with influenza in case-control study nested in a cohort of Japanese employees.
BACKGROUND & AIMS
Several intervention studies have examined the effect of vitamin D supplementation on influenza or influenza-like illness, but their results have been inconsistent. We prospectively examined the association of serum 25-hydroxyvitamin D with influenza among Japanese workers.


METHODS
We conducted a nested case-control study in a cohort of workers in 4 companies in the Kanto and Tokai areas of Japan. Physician-diagnosed influenza that occurred during the winter season was ascertained using a self-administered questionnaire. Two controls matched by company, sex, and age (and checkup date in 1 company) were selected for each case. Serum 25-hydroxyvitamin D concentrations at baseline were measured using a competitive protein binding assay. Odds ratio of influenza were estimated by conditional logistic regression with adjustment for covariates.


RESULTS
Of 182 cases and 364 controls, 179 cases and 353 controls with complete data were included in the analysis. Serum 25-hydroxyvitamin D concentrations were not associated with a significantly lower risk of influenza; the multivariable-adjusted odds ratio for the highest (≥30 ng/mL) versus lowest category (<20 ng/mL) was 0.77 (95% confidence interval 0.37-1.59) (P for trend = 0.80). In a subgroup of participants without vaccination, vitamin D sufficiency (≥30 ng/mL) was associated with a significantly lower risk of influenza (odds ratio 0.14; 95% confidence interval 0.03-0.74).


CONCLUSIONS
Overall, circulating 25-hydroxyvitamin D concentrations were not appreciably associated with influenza episodes. However, the lower influenza risk associated with vitamin D sufficiency among unvaccinated participants warrants further investigation.
['Nanri|Akiko|A|', 'Nakamoto|Kengo|K|', 'Sakamoto|Nobuaki|N|', 'Imai|Teppei|T|', 'Akter|Shamima|S|', 'Nonaka|Daisuke|D|', 'Mizoue|Tetsuya|T|']
D000328:Adult D044466:Asians D015992:Body Mass Index D016022:Case-Control Studies D015331:Cohort Studies D015444:Exercise D005260:Female D006801:Humans D007251:Influenza, Human D007564:Japan D008297:Male D008875:Middle Aged D012307:Risk Factors D012621:Seasons D011795:Surveys and Questionnaires D014807:Vitamin D D014808:Vitamin D Deficiency
Serum 25-hydroxyvitamin D Influenza Japanese Vitamin D Nested case-control studies