The anticarcinogenic potential of green tea and coffee might be expected to reduce the risk of thyroid cancer, but epidemiological evidence is sparse. We examined green tea and coffee consumption in association with thyroid cancer risk in a general Japanese population.

We analyzed data from a prospective cohort of 100,507 persons (48,802 men; 51,705 women) aged 40–69. Green tea and coffee consumption were assessed via a self-administered questionnaire. During a mean 14.2-year follow-up, we documented 159 thyroid cancer cases (26 in men; 133 in women), and Cox regression were used to calculated hazard ratios (HRs).

Green tea consumption was not found to be associated with thyroid cancer risk in general. However, when women were stratified by menopausal status, the multivariable HR for ≥5 cups/day versus <1 cup/day was 1.66 (95% confidence interval (CI) = 0.85–3.23, trend p = 0.04) in premenopausal women, and was 0.47 (95% CI = 0.23–0.96, trend p = 0.06) in postmenopausal women. We found no association between coffee consumption and thyroid cancer risk in either sex.

High green tea consumption may be positively associated with premenopausal thyroid cancer risk, but inversely associated with postmenopausal thyroid cancer risk.