Cigarette smoking, alcohol consumption and the risk of thyroid cancer in Japan: The JPHC Study.

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Although cigarette smoking and alcohol consumption are established causes of cancer, most cohort studies and meta-analyses have reported inverse associations with thyroid cancer (TC) risk. However, epidemiological evidence for this possibility is limited in Asia, where TC histologic type differs from the West. Here, we examined the association between cigarette smoking or alcohol consumption and risk of TC in Japanese. We analyzed data from 101,849 Japanese of the Japan Public Health Center-based Prospective Study (JPHC Study). Cigarette smoking and alcohol consumption were assessed at baseline using a self-administered questionnaire. Cox proportional hazards regression models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (95% CIs). During a mean 18.7 years of follow-up, we identified 232 incident cases of TC. The multivariable adjusted HRs (95% CIs) in current cigarette smoking with ≥20 pack-years compared with never smoking were 0.65 (0.39-1.06) and 0.45 (0.23-0.88) combined for both sexes. After detailed adjustment for cigarette smoking, compared with no current alcohol consumption, HRs (95% CIs) were 0.90 (0.61-1.33) for any current consumption and 0.81 (0.33-1.97) for ≥300 g ethanol/week consumption combined for both sexes. We observed an inverse association between cigarette smoking and TC in Japan. While an inverse association between alcohol consumption and TC is suggested, the CI was wide and included 1. Cigarette smoking was shown to be potentially inversely associated with TC in Japanese, providing insight into risk factors in Asians. Further studies with larger sample sizes are needed to verify these findings.