Serum leptin in elderly people: Associations with sex hormones, insulin, and adipose tissue volumes

Objective: There are few data for associations of serum leptin with body fa t, fat distribution, sex hormones, or fasting insulin in elderly adults. We hypothesized that the sex difference in serum leptin concentrations would disappear after adjustment for subcutaneous, but not visceral body fat. Ser um leptin would not be associated with sex hormone concentrations or serum fasting insulin after adjusting for body fat and fat distribution. Research Methods and Procedures: Subcutaneous adipose tissue (SAT) and visc eral adipose tissue (VAT) volumes were measured using magnetic resonance im aging in a cross-sectional sample of 56 nondiabetic, elderly men and women aged 64 years to 94 years. Serum leptin, sex hormones (testosterone and est rone), sex hormone-binding globulin, and fasting insulin were also measured . Nine women were taking hormone replacement, and five men were clinically hypogonadal. Results: Leptin was significantly associated with both SAT and VAT in each sex. Adjustment for SAT reduced the sex difference in leptin by 56%, but ad justment for VAT increased the difference by 25%. Leptin was not associated with serum estrone or hormone replacement therapy in the women, but had a significant, negative association with testosterone in the men that was ind ependent of SAT, but not VAT. Leptin was significantly associated with fast ing insulin in both sexes independent of age, sex hormones, sex hormone-bin ding globulin, VAT and SAT. Discussion: Sex difference in serum leptin is partly explained by different amounts of SAT. Studies including both men and women should adjust for SAT rather than total body fat that includes VAT. The sex difference in serum leptin is not due to estrogen, but may be partly explained by testosterone. Testosterone is negatively associated with leptin in men, but the associat ion is confounded with VAT. Leptin is associated with fasting insulin in no ndiabetic elderly men and women independent of body fat, fat distribution, or sex hormones.