Anthropometric factors and physical activity and risk of thyroid cancer in postmenopausal women

To investigate the associations of anthropometric factors and physical activity with risk of thyroid cancer in a large prospective study. We examined these associations with risk of incident thyroid cancer in a cohort of 144,319 postmenopausal women enrolled in the Women's Health Initiative. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (95% CI) for factors of interest with risk of all thyroid cancer (n = 294) and of the two major subtypes: papillary (n = 245) and follicular thyroid cancer (n = 32). After adjustment for covariates, measured height at baseline was positively associated with thyroid cancer overall (HR for highest vs. lowest quartile 1.48, 95% CI 1.04-2.13, p for trend 0.02) and with papillary carcinoma (HR 1.49, 95% CI 1.01-2.21, p for trend 0.03, respectively). For each 5 cm-increase in height, the HR for all thyroid cancer was 1.15, 95% CI 1.04-1.27 and for papillary thyroid cancer was 1.14, 95% CI 1.03-1.27. In addition, self-reported weight at age 18 was positively associated with risk of papillary thyroid cancer. In contrast, baseline weight, body mass index, waist circumference, hip circumference, waist-hip ratio, weight change from age 18 to baseline, and level of self-reported recreational physical activity were not associated with risk. Our results suggest that attained stature is a risk factor for thyroid cancer in postmenopausal women. This association may reflect the influence of either genetic or environmental factors in early life on risk of thyroid cancer.