Longitudinal study of leptin concentrations during puberty: Sex differences and relationship to changes in body composition

Leptin may have a role in the initiation of puberty and the regulation of s ubsequent weight gain, but this hypothesis has not been tested by longitudi nal study. We report data from 40 normal children (20 boys and 20 girls) fo llowed from 8-16 yr of age with hormone measurements and auxology every 6 m onths. Before the onset of puberty, leptin levels were similar in boys and girls: G1, mean (95% confidence interval), 2.63 (2.17-3.20) ng/mL; B1, 2.47 (2.08-2.94) ng/mL (P = 0.64) and increased with age in both sexes (B, 0.10 7 +/- 0.042; P = 0.02). With the onset of puberty, leptin levels increased in girls (B2-B5, P < 0.0005), but decreased in boys (G2-G5, P < 0.0005). Si milar positive independent relationships were seen between leptin and fat m ass in girls (B, 0.106 +/- 0.022; P < 0.0005) and boys (B, 0.121 +/- 0.020; P < 0.0005), and negative relationships were found with fat-free mass [gir ls: B, -1.104 +/- 0.381 (P < 0.005); boys: B, -1.288 +/- 0.217 (P < 0.0005) ]. Girls gained more fat mass than boys, whereas boys gained more fat-free mass, and this explained the sex difference in leptin levels. Leptin levels correlated significantly with a large number of other hormones, but none w as independent of changes in body composition. In girls, but not in boys, l ow leptin levels during prepuberty (B1) predicted subsequent gains in the p ercent body fat during puberty (r = -0.75; P = 0.005). The sexual dimorphis m in leptin levels during puberty reflects differential changes in body com position. Prepubertal leptin levels in girls also predict gains in the perc ent body fat.