The gender differences in growth hormone-binding protein and leptin persist in 80-year-old men and women and is not caused by sex hormones

OBJECTIVE Leptin and growth hormone-binding protein (GHBP) both show gender differences that might be explained by sex hormones. To study the potential relevance of oestradiol and testosterone, we have examined 80-year-old subjects in whom oestradiol is higher in men than in women. The interrelationships between leptin, insulin, GHBP and fat mass in this age group were also investigated. DESIGN AND SUBJECTS Ninety-four subjects (55 females and 39 males), all 80 years old, were investigated in a community-based study. None of the investigated subjects was being treated for diabetes mellitus and none of the women had oestrogen replacement. METHODS Levels of testosterone, oestradiol, SHBG, IGF-I, GHBP, glucose, insulin and leptin were analysed. Body composition was measured with bioimpedance analysis (BIA). RESULTS As in younger age groups, serum leptin, the ratio leptin/kilogram fat mass and serum GHBP were higher in the women (all, P <= 0.007), although serum oestradiol was higher in the men (P < 0.001). There were no significant associations between sex hormones and leptin or GHBP either in women or in men (all, r < 0.13, P > 0.1). Leptin correlated to kilogram fat mass in both women (r = 0.55, P < 0.001) and men (r = 0.47, P = 0.003), but in contrast, there were no significant correlations between GHBP and fat mass and GHBP and IGF-I, either in women or in men (all, r < 0.24, P > 0.2). Insulin and leptin were significantly associated with GHBP, both in women (r = 0.48, P < 0.001 and r = 0.43, P = 0.001, respectively) and in men (r = 0.40, P = 0.01 and r = 0.34, P = 0.03, respectively). CONCLUSIONS Although the 80-year-old men had higher oestradiol levels than the women, the women had higher levels of leptin and GHBP. There were no correlations between sex hormones and leptin and GHBP, which indicates that the gender differences are not caused by sex hormones in old age. In contrast to studies in younger subjects, GHBP did not correlate to fat mass in the investigated 80-year-old men and women. In the older subjects investigated, as in younger subjects, GHBP was significantly correlated with leptin and insulin.