Background: Alcohol intake has been shown to be inversely associated with thyroid carcinoma, with similar risk estimates observed in females and males. Large population-based analyses are needed to clarify associations by histologic type, beverage type, and potential effect modifiers.
Objectives: To evaluate the associations between alcohol intake and thyroid cancer risk (papillary, follicular, medullary, anaplastic, and unspecified carcinomas), for papillary and follicular carcinoma separately, and by beverage type (beer, wine, and liquor), and to assess heterogeneity by smoking status, region, body mass index (BMI), and education in females and males separately.
Methods: Individual-level data were pooled from 27 prospective cohorts in Europe, Australia, North America, and Asia. The pooled analytic dataset included 2,258,141 adults without cancer who contributed baseline data (1980-2013). Females (median age: 55 years; 10th–90th percentiles: 37–68) and males (60 years: 47–69) were followed for median periods of 16 (7–22) and 14 (4–20) years, respectively. Baseline alcohol intake (g of ethanol/day), diet, lifestyle, medical, and socioeconomic factors were self-reported. Incident thyroid cancers were ascertained during follow-up. Multivariable Cox models estimated hazard ratios (HR) and 95% confidence intervals (CIs) for alcohol intake (continuous and categorical) and thyroid cancer risk overall, by histologic type, and by beverage type. Heterogeneity was evaluated by smoking status, region, BMI, and education in females and males separately.
Results: During follow-up, 4,321 thyroid cancer cases occurred in females and 839 in males. Each 10 g/day increase in alcohol intake was inversely associated with thyroid cancer risk in females (HR 0.94; 95% CI: 0.90–0.98) and males (HR 0.94; 95% CI: 0.89–0.98). Compared with 0.1–<5 g/day, females consuming 15–<30 g/day had a 20% lower risk (HR 0.80; 95% CI 0.69–0.92), with no association at ≥30 g/day; males consuming ≥30 g/day had a 34% lower risk (HR 0.66; 95% CI 0.51–0.86). Inverse associations were observed for papillary carcinoma in females (HR per 10 g/day 0.92; 95% CI 0.86–0.97; HR 0.72; 95% CI 0.60–0.86 for 15–<30 vs. 0.1–<5 g/day; 2,297 cases) and males (HR per 10 g/day 0.94; 95% CI 0.88–0.99; HR 0.63; 95% CI 0.45–0.87 for ≥30 vs. 0.1–<5 g/day; 549 cases), with no clear association for follicular carcinoma (378 cases in females and 145 in males). By beverage type, inverse associations were observed only for alcohol from wine in females (HR per 10 g/day 0.91; 95% CI: 0.86–0.97) and alcohol from beer in males (HR per 10 g/day 0.90; 95% CI: 0.81–0.99). In females, inverse associations were similar across categories of smoking status, education, BMI, and region (all p for heterogeneity >0.10). In males, inverse associations differed by region (p-heterogeneity= 0.02), being stronger in Europe/Australia and Asia, and education (p-heterogeneity = 0.03), being stronger in males with lower education.
Conclusions: Alcohol intake was inversely associated with thyroid cancer, mainly for papillary carcinoma, with beverage-specific patterns and heterogeneity by region and education in males. These observational findings warrant cautious interpretation and should not be taken as a recommendation to consume alcohol; further work is needed to clarify mechanisms and disentangle correlated behaviors.