Racial differences in serum levels of adiponectin and leptin

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Obesity is an important modifiable risk factor for several cancer sites. The adipokines, including leptin and adiponectin, are a group of proteins produced in adipose tissue that have been associated with obesity and insulin regulation and are also associated with risk of breast, colorectal, endometrial, prostate, and other cancers. Racial disparities in cancer incidence and mortality are well documented as are racial differences in body size. Biomarkers of adiposity also may differ by race, providing a promising research approach to better understand the mechanisms linking obesity and cancer risk among people of different races. Serum levels of adiponectin and leptin were measured in a stratified random sample of 792 Southern Community Cohort Study participants using blood samples collected at study enrollment. These participants enrolled at community health centers across the southeastern United States between 2002 and 2004, were between the ages of 40 and 79, and self-reported their race as either white (N=396) or black (N=396). Cross-sectional analyses were employed to compare serum levels of log-transformed leptin and log-transformed adiponectin across gender and race groups, after adjusting for correlates of these markers using multiple linear regression models. Adjusted geometric mean leptin levels were similar between black and white men (4.45 v. 4.51 ng/ml, p=0.89) but were higher among black women compared to white women (17.44 v. 14.38 ng/ml, p=0.03). Adjusted geometric mean adiponectin levels were lower in both black men compared to white men (10.25 v. 14.37 ug/ml, p<0.0001) and black women compared to white women (13.02 v. 21.18 ug/ml, p<0.0001). Body mass index (BMI) was the most important predictor of leptin and adiponectin in all race and gender groups. In addition to BMI, age was positively associated with leptin among black and white males, and physical activity, education, and high-density lipoprotein (HDL) cholesterol were also significant predictors of leptin in black males. Physical activity was negatively associated with leptin among both black and white females and age and smoking were also associated with leptin in white females. In prediction models for adiponectin, HDL cholesterol and smoking were positive predictors among black and white males while only HDL cholesterol was significant among black and white females. This study, with its relatively large sample size and similar socioeconomic status and common geographic location for blacks and whites contributes to a growing literature regarding racial differences in the adipokines. We identified significant racial differences in serum levels of leptin among females and in adiponectin levels among both males and females even after adjusting for obesity and other determinants of these markers. Our results suggest that future research is needed to clarify possible mechanistic roles that leptin and adiponectin play in relation to obesity, cancer risk, and race.