Green tea consumption and influenza infection among Japanese employees

This study examined the association of green tea consumption with influenza among Japanese workers in the Kanto and Tokai areas. We conducted a case-control study in a cohort of 4302 workers. Consumption frequency of green tea in 2011 and physician-diagnosed influenza that occurred over the winter season from November 2011 through April 2012 were ascertained using a self-administered questionnaire. Two controls matched by company, sex, and age (and checkup date in one company) were randomly selected for each case. Odds ratio of influenza were estimated by conditional logistic regression. One hundred and seventy-nine cases and 353 controls with complete data were included in the analysis. Green tea consumption was significantly associated with decreased odds of developing influenza; the multivariable-adjusted odds ratio for green tea consumption of ≥5 cups/week was 0.61 (95% CI 0.39-0.95) compared with <1 cup/week (P for trend = 0.028). When analysis was restricted to cases confirmed using a diagnostic kit, the corresponding value was 0.68 (95% CI 0.39-1.18; P for trend = 0.16). Our data suggest that green tea consumption is associated with a lower risk of influenza. The present findings require confirmation in large-scale prospective studies using diagnostic tool for influenza infection.