Lifestyle and risk of follicular lymphoma: a systematic review and meta-analysis of observational studies

To investigate the relationship between follicular lymphoma (FL) risk and common modifiable lifestyle factors, specifically smoking, alcohol, body mass index (BMI), and hair dye use. We performed a systematic review and meta-analysis of observational studies published prior to 01 January 2020. We searched Ovid MEDLINE, Ovid EMBASE, and Web of Science and the reference lists of original studies and review articles. We used random-effects models to generate meta-estimates of relative risk (RR) with 95% confidence intervals (95% CI). Twenty-four cohort and ten case–control studies were eligible. Ten articles examined smoking, 11 alcohol, 13 BMI, and four hair dye use and risk of FL. The meta-estimate for current smoking was 1.11 (95% CI 0.92–1.35; I2 = 51%) and there was no significant dose–response per 5-year increase in duration (p-trend = 0.087). Current alcohol intake was inversely associated with FL risk (meta-RR 0.87, 95% CI 0.81–0.94; I2 = 0%) and there was a significant dose–response per 5 drinks/week increase in intake (p-trend = 0.008). There was no association with 5 kg/m2 increase in early adulthood BMI (meta-RR 1.05, 95% CI 0.91–1.20; I2 = 7%) or being overweight (meta-RR 0.99, 95% CI 0.92–1.07; I2 = 0%) or obese (meta-RR 1.08, 95% CI 0.99–1.17; I2 = 0%) as an adult. Hair dye use before 1980 was positively associated with FL risk (meta-RR 1.66, 95% CI 1.22–2.25; I2 = 55%) and no evidence of effect after 1980. We found consistent evidence of an inverse association between current alcohol intake and FL risk, and a significant increased risk with hair dye use before 1980. The evidence for smoking is heterogeneous, but most studies did not support an association. Further research is required to understand the mechanisms underlying these associations and the potential for prevention strategies.