Smoking and alcohol consumption in relation to risk of thyroid cancer in postmenopausal women

Few cohort studies have examined smoking and alcohol consumption in relation to risk of thyroid cancer, and their findings are conflicting.

We therefore assessed the association of smoking and alcohol intake with risk of thyroid cancer in a cohort of 159,340 women enrolled in the Women's Health Initiative. Over 12.7 years of follow-up 331 cases of thyroid cancer, of which 276 were papillary thyroid cancer, were identified. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI).

Compared to never smokers, ever smokers did not have altered risk. Current smokers had reduced risk for all thyroid cancer (HR 0.54, 95% CI 0.29-1.00) and for papillary thyroid cancer (HR 0.34, 95% CI 0.15-0.78); however, the number of current smokers among cases was small. No associations or trends were seen for amount smoked, age of starting smoking, or age at quitting. Smokers of ≥40 pack-years had a significantly reduced risk of papillary thyroid cancer (HR 0.44, 95% CI 0.21-0.89). In contrast, women who had smoked for < 20 years had increased risk of thyroid cancer (HR 1.35, 95% CI 1.05-1.74) and papillary cancer (HR 1.43, 95% CI 1.09-1.89). Alcohol intake was not associated with risk.

Our findings suggest that current smoking and having higher pack-years of exposure are associated with a modestly reduced risk of thyroid cancer, whereas alcohol consumption does not appear to affect risk.