Serum immunoreactive leptin concentrations in a Canadian Aboriginal population with high rates of NIDDM

OBJECTIVE - To better understand the relationship between leptin and the anthropometric and physiological variables associated with diabetes, we measured this protein in an isolated Canadian aboriginal population with very high rates of NIDDM. RESEARCH DESIGN AND METHODS - There were 728 individuals aged 10-79 years who participated in a population-based survey to determine the prevalence of NIDDM and its associated risk factors. Fasting blood samples for glucose, insulin, triglyceride, and leptin were collected; a 75-g oral glucose tolerance test was administered and a second blood sample drawn after 120 min. Height, weight, and waist and hip circumferences were determined, and percent body fat was estimated using biological impedance analysis. Fitness level was assessed in a subsample of individuals using a validated submaximal step test. The relationship between serum leptin and the other variables was assessed using Spearman's correlation coefficients and multiple linear regression. RESULTS - Serum leptin concentration was strongly correlated with adiposity, and levels were substantially higher in female subjects in all age-groups. For male subjects, percent body fat, fasting insulin level, and waist circumference were significant independent predictors of log serum leptin concentration in a multiple linear regression model (R-2 = 0.582). For female subjects, these variables plus glucose tolerance status were included in the final model (R-2 = 0.633). Fitness level, when included with the main effects of the above models, was a significant predictor for male subjects only. CONCLUSIONS - In an isolated aboriginal community with high rates of diabetes, we found significant independent relationships between leptin and percent body fat and between leptin and fasting insulin. As documented in other populations, the higher leptin concentration among female subjects may reflect differential leptin production from different adipose tissue beds, or leptin resistance. Independent relationships also existed among leptin and glucose tolerance status in female subjects and fitness level in male subjects.