Association between Obesity Indexes and Thyroid Cancer Risk in Korean Women: Nested Case-Control Study

Abstract

Simple Summary Regarding the association between obesity and thyroid cancer, most previous studies have focused only on body mass index (BMI), but other measures of obesity have not been studied much with inconsistent results. This study showed a significant association between increased abdominal obesity indexes, such as waist circumference (WC, >= 85.0 cm) and waist-height ratio (WHTR >= 0.5) as well as BMI (>= 25.0 Kg/m(2)), and increased risk of thyroid cancer. In addition, people who had both abnormally obese levels of BMI and other obesity indexes including WC, waist-hip ratio, or WHTR showed an increased risk of thyroid cancer, compared to those with normal levels of BMI and each obesity index. These results provide evidence of the contribution of both total and central adiposity across the lifespan to thyroid cancer incidence. Risk factor modifications must be considered to explain the current thyroid cancer epidemic. Objective: This study aimed to identify the association between various obesity indexes, including waist circumference (WC), waist-hip ratio (WHR), waist-height ratio (WHTR), and BMI, and their combinations with body mass index (BMI) and thyroid cancer risk. Methods: Of the 65,639 participants who completed a follow-up survey of the Health Examinee Study (HEXA), a prospective cohort of the Korean Genome and Epidemiology Study, 412 female incident thyroid cancer cases, and 1648 birth year- and enrollment year-matched female controls were included. Multiple conditional logistic regression was used to estimate the association between obesity indexes and thyroid cancer risk. Results: The risk of developing thyroid cancer was increased by 1.37-fold (95% confidence interval (CI) = 1.03-1.81) higher in the obese BMI group (>= 25.0 Kg/m(2)) compared to that in the normal BMI group (<23.0 Kg/m(2)). Obesity in terms of WC (>= 85.0 cm) and WHTR (>= 0.5) was associated with an increased risk of thyroid cancer (OR 1.55, 95% CI = 1.16-2.07; OR 1.37, 95% CI = 1.07-1.75, respectively). However, increased WHR levels did not show any significant association. Women with both obese levels of BMI (>= 25.0 Kg/m(2)) and other obesity indexes (WC >= 85.0 cm, WHR >= 0.85, or WHTR >= 0.5) showed an increased risk of thyroid cancer with OR of 1.63 (95% CI = 1.14-2.31), 1.49 (95% CI = 1.05-2.12), and 1.42 (95% CI = 1.04-1.94), compared to those with normal levels of BMI and each obesity index. Conclusion: These results provide evidence of the contribution of both total and central adiposity across the lifespan of thyroid cancer incidence. Risk factor modifications must be considered to explain the current thyroid cancer epidemic.