Body mass index and incidence of thyroid cancer in Korea: the Korean Cancer Prevention Study-II

Purpose The prevalence of thyroid cancer and obesity has increased worldwide. However, their association has remained controversial and few studies have been performed in Asia. Our study evaluated the correlation between the incidence of thyroid cancer and body mass index (BMI) in Korea. Methods This is a multi-centered, prospective cohort study from the Korean Cancer Prevention Study-II. A total of 141,157 individuals between 1994 and 2012, including 1546 newly developed thyroid cancer patients, were enrolled. Subjects were divided into four groups on the BMI. Person-years, incidence rate, and hazard ratios (HRs) were calculated using the Cox proportional hazard model. Results The increasing trends of HRs of thyroid cancer in men and women younger than 50 years of age were observed as BMI increased (P trend <0.001 in both groups). However, in women older than 50 years of age, there was no association between thyroid cancer incidence and BMI. Conclusions Our findings suggest that positive association between thyroid cancer incidence and high BMI in men and women under 50 years old. Based on these results, we suggest that obese men and women under 50 years old are better to be considered for the higher possibility of thyroid cancer development, and more efforts are needed to control weight gain.