Sex-specific Associations between Body Mass Index and Thyroid Cancer Incidence among Korean Adults

Background: The potential differences by sex in the association between body mass index (BMI) and thyroid cancer risk remain unconfirmed.

Methods: Data from the National Health Insurance Service-National Health Screening Cohort (NHIS-HEALS; 2002-2015; population size = 510,619) and the Korean Multi-center Cancer Cohort (KMCC) data (1993-2015; population size = 19,026) were used. We constructed Cox regression models, adjusted for potential confounders, to evaluate the association between BMI and thyroid cancer incidence in each cohort, and assessed the consistency of the results.

Results: In the NHIS-HEALS, 1,351 and 4,609 incident thyroid cancer cases occurred during the follow-up among men and women, respectively. Compared with BMI of 18.5-22.9 kg/m2, BMI of 23.0-24.9 [no. of cases = 410; HR, 1.25; 95% confidence interval (CI), 1.08-1.44], 25.0-29.9 (no. of cases = 522; HR, 1.32; 95% CI, 1.15-1.51), and ≥30.0 kg/m2 (no. of cases = 48; HR, 1.93; 95% CI, 1.42-2.61) were associated with an increased risk of incident thyroid cancer among males. Among females, BMI of 23.0-24.9 (no. of cases = 1,300; HR, 1.17; 95% CI, 1.09-1.26) and 25.0-29.9 (no. of cases = 1,406; HR, 1.20; 95% CI, 1.11-1.29) were associated with incident thyroid cancer. The analyses using the KMCC demonstrated results consistent with wider CIs.

Conclusions: Sex differences in the associations between BMI and thyroid cancer incidence were observed in Korean cohorts.

Impact: BMI <23 kg/m2 may help prevent incident thyroid cancer, especially among men.