The relationship between physical activity and lymphoma: a systematic review and meta analysis.
BACKGROUND
The literature suggests an increased risk between anthropometrics including higher body mass index and lymphoma incidence; however, the association with physical activity remains unclear. A systematic review/meta-analysis was therefore performed to examine this association with physical activity (total, recreational or occupational).


METHODS
PubMed, Web of Science and Embase were reviewed from inception to October 2019 identifying relevant observational studies. Non-Hodgkin lymphoma (NHL) including subtypes diffuse large B cell lymphoma, follicular lymphoma and chronic lymphocytic leukemia/small lymphocytic lymphoma, and Hodgkin lymphoma (HL) were analyzed. Included studies reported activity, lymphoma cases, effect size and variability measures, and were restricted to human subjects of any age. Data was pooled generating summary relative risk (RR) estimates with 95% confidence intervals (CI) using random-effects models with primary outcome of histologically confirmed incident lymphoma.


RESULTS
One thousand four hundred studies were initially identified with 18 studies (nine cohort, nine case-control) included in final analysis. Comparing highest vs. lowest activity categories was protective for all lymphoma (RR 0.89, 95%CI 0.81-0.98). Sensitivity analysis demonstrated effect persistence within case-control studies (RR 0.82, 95% CI 0.71-0.96), but not cohort studies (RR 0.95, 95%CI 0.84-1.07). Borderline protective effect was seen for NHL (RR 0.92, 95%CI 0.84-1.00), but not HL (RR 0.72, 95%CI 0.50-1.04). Analysis by NHL subtype or gender showed no effect. Dose response analysis demonstrated a protective effect (p = 0.034) with a 1% risk reduction per 3 MET hours/week (RR 0.99, 95%CI 0.98-1.00).


CONCLUSIONS
Physical activity may have a protective effect against lymphoma development; further studies are required to generate recommendations regarding health policy.


TRIAL REGISTRATION
This study was registered prospectively at PROSPERO: CRD42020156242 .
['Davies|Gwynivere A|GA|http://orcid.org/0000-0003-4472-6535', 'Strader|Christopher|C|', 'Chibbar|Richa|R|', 'Papatheodorou|Stefania|S|', 'Dmytriw|Adam A|AA|']
D015992:Body Mass Index D016022:Case-Control Studies D015331:Cohort Studies D015444:Exercise D006801:Humans D015994:Incidence D008228:Lymphoma, Non-Hodgkin D064887:Observational Studies as Topic
Physical activity Lymphoma Meta-analysis