To examine the relationship between leptin, adiponectin and insulin resistance in a group of men and women with varying degrees of glucose tolerance and obesity.
69 participants were investigated and divided into four groups: 15 normal weight with normal glucose tolerance (NW NGT); 22 overweight with normal glucose tolerance (OW NGT); 15 overweight with impaired glucose tolerance (OW IGT); and 17 overweight with diabetes mellitus (OW DM). Blood was analysed for glucose, insulin, leptin, adiponectin and triglycerides. Body composition was determined by impedance. Ethical approval was obtained from the local ethics committee. Data are presented as mean±S.E.M.
There were significant differences between groups for triglycerides, adipokines, and measures of insulin resistance (plasma glucose, insulin and HOMA at 0 and 120 minutes, respectively). There was a strong positive correlation between fasting leptin and fat mass (r=0.79, P<0.001), and negative correlation between adiponectin and lean body mass (r=−0.36, P<0.01). Adiponectin concentration varied considerably in subjects with similar degrees of body composition, and females (n=43, 9.5 μg/ml ±1.6) having significantly higher concentrations than males (n=26, 4.4 μg/ml ±0.8) in spite of similar insulin sensitivity (HOMA 0 female =4.3±0.5; male =4.4±0.6). Stepwise multiple regression analysis showed fasting leptin accounted for approximately 30% of variation in fasting HOMA, with triglycerides accounting for a further 15% variation. However, adiponectin failed to contribute to the variation in insulin resistance in this model.
Serum leptin and triglycerides were strong determinants for insulin resistance. The significantly lower adiponectin levels in men could be explained by their higher lean body mass.