| Currently there is no compelling evidence that circulating leptin concentrations predict regional body fat distribution. Similarly, previous studies in humans have indicated no or only weak relationships between bone outcomes and circulating leptin. We studied effects of circulating leptin on regional body composition and bone mineral content (BMC) dual energy x-ray absorptiometry (DXA) in 345 Hutterite (n = 264, n = 152 female) and non-Hutterite (n = 81, n = 46 female) individuals ages 20 to 55 years. We tested the following hypotheses: (1) There will be a strong correlation between whole body (WB) percentage (%) fat mass and circulating leptin concentrations. (2) Controlling for covariates, there will be no relationship between trunk percentage fat mass and circulating leptin concentrations. (3) Controlling for covariates, there will be no relationships between WB, lumbar, hip, or regional BMC and circulating leptin concentrations.; Using simple linear regression, we observed strong correlations between WB % fat and log-transformed circulating leptin (log-leptin) concentrations among females (R2 = 0.74, p ≤ 0.001) and males (R 2 = 0.82, p ≤ 0.001). To test hypotheses 2 and 3, we performed stepwise multiple regression separately by sex and controlled for nutrient intakes, physical activity, anthropometrics, grip strength, and estrogen status. Log-leptin persisted in multiple regression models predicting trunk % fat for both females (p ≤ 0.05) and males (p ≤ 0.001).; In males, relative log-leptin (log-leptin/WB fat mass) was positively associated with trunk % fat among lean {lcub}body mass index (BMI) < 25 kg/m 2{rcub}, but inversely associated with trunk % fat in obese (BMI ≥ 30 kg/m2) (p ≤ 0.001 for BMI category*relative log-leptin, both models).; Among females, we found a positive independent effect of log-leptin on lumbar spine (p ≤ 0.001) BMC, but a negative effect on trunk and arm BMC. Log-leptin did not independently predict any BMC outcomes in males.; Our data show that a sexual dimorphism exists in the bone response to circulating leptin. Importantly, it is likely that the beneficial effect of obesity on bone density is mediated by leptin in the primarily trabecular, fracture susceptible lumbar site in females. Studies to determine potential confounding effects of sex hormones on leptin's relationship with BMC are essential. |
