Abstract CN02-04: Racial/ethnic differences in the association between body composition/fat distribution and circulating hormones and metabolic factors in U.S. men

Background: Body composition and fat distribution vary by race/ethnicity and these differences are thought, in part, to explain racial/ethnic differences in common chronic disease risk. Obesity may influence those common chronic diseases via alterations in circulating factors, including sex steroid hormones, insulin, lipoproteins, adipokines and growth factors. We previously observed that obesity is associated with lower testosterone and higher estradiol concentrations adjusting for race/ethnicity. We also previously saw that serum testosterone was highest in Mexican-American (MA) compared with non-Hispanic black (NHB) and white (NHW) men, and estradiol concentration was highest in NHB compared with NHW and MA men adjusting for adiposity. The present aim was to evaluate whether the association of body composition/fat distribution with circulating hormones and metabolic factors perturbed in obesity varies by race/ethnicity in adult men. Methods: We conducted a cross-sectional study in the Third National Health and Nutrition Examination Survey (NHANES III). We measured serum hormone concentrations in stored samples by immunoassay for 1,256 men aged 20+ years who participated in the morning examination session of Phase I. The other circulating factors were measured previously in NHANES. Weight, height, and waist circumference (WC) were measured during the physical examination. Percent body fat (%BF) was calculated from bioelectrical impedance, height, weight, and age. We categorized body composition/fat distribution using combinations of overall (%BF >25%) and central (WC >102 cm) obesity: 1) obese (>25%)/obese (>102 cm), 2) obese (>25%)/non-obese (≤102 cm), 3) non-obese (≤25%)/obese (>102 cm), and 4) non-obese (≤25%)/non-obese (≤102 cm). Geometric mean concentrations in the four categories were compared by race/ethnicity. We used linear regression to adjust for age, smoking, cotinine, alcohol, physical activity, WC, %BF, and mutually for the hormones. Results: In all racial/ethnic groups, men who were obese/obese, obese/non-obese, or non-obese/obese had lower testosterone concentrations than men who were non-obese/non-obese. However, lower testosterone was primarily associated with central obesity in MA men (see bolded values for patterns: ob/ob: 4.23 , ob/n-ob: 5.62, n-ob/ob: 3.28 , n-ob/n-ob: 6.19 ng/mL); with both central and overall obesity in NHB men ( ob/ob: 3.89 , ob/n-ob: 4.64 , n-ob/ob: 4.62 , n-ob/n-ob: 5.70 ng/mL); and with central obesity in NHW men, which was more pronounced in men who had both overall and central obesity ( ob/ob: 4.07 , ob/n-ob: 5.16, n-ob/ob: 4.44 , n-ob/n-ob: 5.82 ng/mL). Patterns were the same for free as for total testosterone. With the exception of HDL and IGF-1, men of all racial and ethnic groups who were obese/obese had higher circulating biomarker concentrations than men who were non-obese/non-obese. Conclusion: In this nationally representative study, the association of adiposity with sex steroid hormones or circulating biomarkers varied by race/ethnicity in adult men. Specifically, WC influenced testosterone to a greater extent than %BF in MA men, whereas both %BF and WC influenced testosterone in NHB men, and WC had the greater influence especially in the presence of high %BF in NHW men. Similarly, WC had a greater effect than %BF on fasting insulin, c-reactive protein and LDL in NHB and MA men. These findings have import in the analysis of adiposity and risk of cancer and other diseases by race/ethnicity.