The risk of thyroid cancer and obesity: A nationwide population-based study using the Korea National Health Insurance Corporation cohort database

Introduction: In recent years, the incidence of thyroid cancer and obesity has increased rapidly worldwide. Many studies have been conducted on the relationship between thyroid cancer and obesity; however, the potential mechanisms are not well understood, and few studies have been performed in Asia. This study aimed to identify the relationship between the risk of thyroid cancer and obesity in the Korean population based on a large cohort of data. Method: We analyzed clinical data from a total of 351,402 individuals (males: 181,709, females: 169,693) aged over 20 years who received medical examinations arranged by the national insurance program from 2003 to 2008. Newly diagnosed thyroid cancer was identified using insurance claims data. The median follow-up duration was 7.01 years. Results: The mean body mass index (BMI) of the subjects was 23.6 +/- 3.2 kg/m 2 (males, 24 +/- 3; females, 23.1 +/- 3.3). A total of 3308 individuals (0.94%) developed thyroid cancer during the study period. The risk of thyroid cancer was higher with increasing BMI in both men and women. Hazard ratios (95% confidence interval) for obese (25-29.9 kg/m(2)) and extremely obese (>30 kg/m(2)) groups were 1.23 (1.13 -1.34) and 1.26 (1.02-1.50), respectively, compared to the normal group (18.5-22.9 kg/m(2)). In particular, the association between the risk of thyroid cancer and BMI was more remarkable in the male group than female group. Conclusion: Our findings show that higher BMI is positively associated with the risk of thyroid cancer. Furthermore, this study supports the positive association between obesity and the increased incidence of thyroid cancer. (C) 2018 Elsevier Ltd. All rights reserved.