Ethnic variation in adiponectin and leptin levels and their association with adiposity and insulin resistance.

Abstract

To investigate ethnic differences in adiponectin and leptin concentration and to determine whether these adipokines and a high-glycemic index diet account for ethnic variation in insulin resistance. In 1,176 South Asian, Chinese, Aboriginal, and European Canadians, fasting blood samples were drawn, and clinical history and dietary habits including glycemic index/glycemic load were recorded using standardized questionnaires. Insulin resistance was defined using homeostasis model assessment-insulin resistance (HOMA-IR). Adiponectin concentrations were significantly higher in Europeans (adjusted mean 12.94 [95% CI 2.27-13.64]) and Aboriginal people (11.87 [11.19-12.59]) than in South Asians (9.35 [8.82-9.92]) and Chinese (8.52 [8.03-9.03]) (overall P < 0.001). Serum leptin was significantly higher in South Asians (11.82 [10.72-13.04]) and Aboriginal people (11.13 [10.13-12.23]) than in Europeans (9.21 [8.38-10.12]) and Chinese (8.25 [7.48-9.10]). BMI and waist circumference were inversely associated with adiponectin in every group except the South Asians (P < 0.001 for interaction). Adiponectin was inversely and leptin was positively associated with HOMA-IR (P < 0.001). The increase in HOMA-IR for each given decrease in adiponectin was larger among South Asians (P = 0.01) and Aboriginal people (P < 0.001) than among Europeans. A high glycemic index was associated with a larger decrease in adiponectin among South Asians (P = 0.03) and Aboriginal people (P < 0.001) and a larger increase in HOMA-IR among South Asians (P < 0.05) relative to that in other groups. South Asians have the least favorable adipokine profile and, like the Aboriginal people, display a greater increase in insulin resistance with decreasing levels of adiponectin. Differences in adipokines and responses to glycemic foods parallel the ethnic differences in insulin resistance.