# Central Adiposity, Obesity, Metabolic Syndrome, and the Risk of Thyroid Cancer in Adults Aged ≥75 Years: A Nationwide Korean Cohort Study

## TL;DR

This study finds that central obesity is strongly linked to thyroid cancer risk in older adults, while metabolic syndrome has a weaker and more specific effect.

## Contribution

The study identifies central adiposity as a dominant risk factor for thyroid cancer in the elderly, particularly in those aged ≥85 years.

## Key findings

- General obesity and central adiposity are robustly associated with thyroid cancer risk in adults aged ≥75 years.
- Metabolic syndrome confers a modest and mainly age- and sex-specific additional risk.
- Central adiposity (waist circumference) showed the most consistent association across models and subgroups.

## Abstract

Thyroid cancer is common in older adults, but the contribution of general and central obesity and metabolic syndrome (MetS) to thyroid cancer risk in very old populations is not well defined. Using a nationwide Korean health screening cohort of adults aged ≥75 years, we examined whether body mass index (BMI), waist circumference (WC), and MetS were associated with incident thyroid cancer, including a dedicated analysis among those aged ≥85 years. Both general obesity and central adiposity were associated with a higher risk of thyroid cancer, and MetS conferred an additional but weaker and mainly age- and sex-specific risk. Central adiposity (abdominal obesity defined by WC) showed the most consistent association across analytic models and subgroups. In contrast, the MetS association was more modest and largely confined to women aged 75–84 years, with attenuation beyond 85 years. Our findings highlight central adiposity as the dominant late-life correlate of thyroid cancer risk, while the contribution of MetS is limited to selected subgroups and becomes imprecise in the oldest-old, in whom competing mortality is substantial.

Background: The contribution of adiposity and metabolic syndrome (MetS) to thyroid cancer risk in late life, particularly among the elderly, is unclear. Methods: We conducted a nationwide cohort study of Korean adults aged ≥75 years who underwent standardized health screening. Exposures were body mass index (BMI), waist circumference (WC), and MetS defined by standard clinical criteria. The incidence of thyroid cancer was determined using administrative data. Fine–Gray sub-distribution hazard models estimated adjusted hazard ratios (HRs) with prespecified stratification by sex and age (75–84 vs. ≥85 years). Results: Among 1,164,707 participants (60.3% women), 2645 incident cases were identified. In the fully adjusted models, obesity (BMI ≥ 25 kg/m2) was associated with a 37% higher hazard (HR, 1.37; 95% confidence interval [CI], 1.27–1.49) and MetS with an 18% higher hazard (HR, 1.18; 95% CI, 1.09–1.28). In sex-stratified models, MetS was associated with thyroid cancer in women (HR 1.19; 95% CI, 1.08–1.31) and showed a similar direction of association in men (HR 1.16; 95% CI, 1.00–1.35), with overlapping CIs. By age, associations were evident at 75–84 years (MetS: HR, 1.18; obesity: HR, 1.36), whereas at ≥85 years, only obesity remained significant (HR, 1.90; 95% CI, 1.13–3.18). Among MetS components, high WC showed the most consistent association (HR, 1.31; 95% CI, 1.21–1.42). Conclusions: In adults aged ≥75 years, general obesity and, in particular, central adiposity are robustly associated with incident thyroid cancer, whereas metabolic syndrome confers a more modest and mainly age- and sex-specific additional risk.