Osteoporosis and obesity are well-known public health concerns, particularly for postmenopausal women. Recently, an increasing research interest has been focused on the adipocyte-secreted hormones, leptin and adiponectin, as potential mediators between adipose tissue and bone. Studies show that both leptin and adiponectin can be either beneficial or harmful to bone depending on the mode of action. This study used the data collected from the longitudinal study of weight loss described elsewhere. The aim of this study was to examine the association of serum leptin, adiponectin, and the leptin-adiponectin ratio (L:A) with bone mineral density (BMD) and bone mineral content (BMC) of various skeletal sites, markers of bone turnover, and body composition (fat and lean mass), respectively. Additionally, the changes in both adipokines with the weight and body composition change during the six-month weight loss program were examined as well. At baseline, participants included (n=184) healthy Caucasian women (BMI range=25.0-40.0 kg/m2, age=55.7±4.4 years, mean±SD). BMD/BMC and body composition were assessed by iDXA. Serum leptin, adiponectin and bone markers (osteocalcin, serum amino- (N-) terminal cross-linking telopeptides of type I collagen (NTx), and urine carboxyl- (C-) terminal cross-linking telopeptides of type I collagen (CTx)) were analyzed with immunoassay kits. Pearson's and partial correlation, multiple regression models controlling for multiple confounders, including age, physical activity, dietary calcium and vitamin D intake as well as BMI, and repeated measures ANOVA were calculated using SPSS. In a cross-sectional analysis at baseline, serum leptin and L:A ratio were significantly positively correlated with BMD at the femoral neck, total femur and forearm before and after controlling for age, physical activity, and dietary intake of calcium and vitamin D. However, both correlations were lost after controlling for BMI. Multiple regression, with serum leptin or L:A as independent variable, revealed a positive association with both femoral neck and total femur BMD (before and after controlling for the above confounders). After six months, participants (n=100) lost ~3.9% and~ 3.4% of body weight and fat, respectively, as well as some of the bone mass in several skeletal sites (although NS). As expected, serum leptin significantly decreased while adiponectin increased with weight and fat loss. Adiponectin was significantly negatively correlated only with serum NTx before and after controlling for the above confounders. In conclusion, the influence of higher leptin and L:A to bone may be site-specific. A six-month weight loss resulted in slight bone loss and decreased leptin and increased adiponectin levels. The positive effect of leptin on femoral BMD remained, even after weight loss caused decreased levels of it. These findings suggest that leptin may be beneficial to femoral bone in overweight and obese postmenopausal women independent of weight or fat loss.
