Age-related changes in sex hormones affect the sex difference in serum leptin independently of changes in body fat

Serum leptin concentrations are highly correlated with body fatness, but th ere is considerable variability among individuals after adjusting for diffe rences In body fatness. Theoretically, sex hormone levels may influence ser um leptin, since the levels are higher in women than in men independently o f body fat, Increasing old age is associated with decreases in serum sex ho rmone concentrations and changes in body fatness that may independently alt er serum leptin concentrations. In a cross-sectional sample of 106 men and 166 women aged 62 to 98 years, serum leptin adjusted for total body fat had a significant positive association with age in men and a nonsignificant ne gative association with age in women. Serum testosterone had a significant negative association with serum leptin in men after adjusting for total bod y fat, the fasting insulin resistance index (FIRI), and sex hormone-binding globulin (SHBG). In a longitudinal sample of 22 elderly men and 52 women, serum leptin levels increased significantly over a 14-year period in men, b ut not in women. Increases in serum leptin were significantly associated wi th decreases in serum testosterone but not with changes in the body mass in dex (BMI) in men. In contrast, changes in leptin were associated with chang es in the BMI but not with changes in serum estrone in women. These results suggest that differences among men and changes with age in serum leptin ar e associated with circulating levels of testosterone, Elderly men become pr ogressively "hyperleptinemic" with age regardless of changes in body fatnes s, possibly due to decreasing; testosterone levels, Copyright (C) 1999 by W .B. Saunders Company.