Metabolic disease and risk for thyroid cancer in a predominantly Black and low-income cohort

Background: Thyroid cancer incidence and mortality are rising in the U.S., as is metabolic disease. Some studies have shown in predominantly Non-Hispanic White populations that obesity and diabetes are positively associated with thyroid cancer risk while physical activity is inversely associated. However, comparatively little is known about metabolic diseases as risk factors for thyroid cancer among Black Americans and low-income Americans, despite a high prevalence of these factors within these populations. Methods: The Southern Community Cohort Study is a prospective cohort study of >84,000 participants enrolled between 2002 to 2009 designed to evaluate the etiology of cancer and other health conditions in the southeastern U.S. states including for Black individuals (~2/3) and individuals with low income (~1/2). Self-reported body mass index (BMI), diabetes diagnosis, and physical activity levels were collected at baseline. Thyroid cancer incidence was ascertained through state cancer registry linkages. BMI was categorized as normal/underweight: <25 kg/m 2 , overweight: 25-<30 kg/m 2 , and obese: ≥30 kg/m 2 . Participants with missing data were excluded, leaving 68,532 participants and 135 incident cases. We used Cox proportional hazards models adjusted for potential confounders to evaluate risk factors for thyroid cancer overall and stratified by sex, self-reported race, and income. Results: The mean enrollment age was 51.8 years, with a median follow-up of 12.6 years. In comparison to normal/underweight, being overweight (HR: 2.39; 95% CI: 1.30-4.40) or having obesity (HR: 2.56; 95% CI: 1.44-4.58) were both associated with increased thyroid cancer risk ( P trend : <0.01). These associations were also observed for female participants (HR: 2.55; 95% CI: 1.26-5.20 and HR: 2.55; 95% CI: 1.30-5.00, respectively; P trend : 0.02). Obesity was also associated with increased risk for Non-Hispanic Black participants (HR: 2.81; 95% CI: 1.19-6.63; P trend : 0.02) and for those with household income <$15,000 (HR: 5.42; 95% CI: 1.92-15.3; P trend : <0.01). No statistically significant association was observed for obesity among those with higher income although being overweight was associated with a two-fold increased risk in comparison to normal/underweight. Neither overweight nor obesity was associated with risk for male or Non-Hispanic White participants, possibly due to a smaller sample size. History of diabetes and physical activity were not independently associated with thyroid cancer risk. Conclusions: Thyroid cancer risk is associated with obesity in a predominantly Black and low-income population, in line with previous findings in other populations. However, neither diabetes nor physical activity were associated. These findings suggest that obesity prevention and treatment should be evaluated as potential prevention strategies for thyroid cancer risk.