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Background: Obesity is associated with hyperparathyroidism and increased bone mass and turnover, but their pathogeneses are unclear., Aims: Our aim was to determine in obesity interrelationships among serum levels of leptin, the mineral-regulating hormones, bone turnover markers, and sclerostin., Methods: This case-control study was performed in 20 women having bariatric surgery and 20 control women matched for race and age. Anthropometrics and fasting serum biochemistries were measured in controls and in bariatric patients the morning of surgery., Results: Body mass index (48.9 vs. 25.4 kg/m(2)), weight (128.6 vs. 71.9 kg), serum leptin (74.6 vs. 25.2 ng/ml), PTH (44.5 vs. 28.8 pg/ml), fibroblast growth factor 23 (FGF23) (42.4 vs. 25.9 pg/ml), and bone alkaline phosphatase (BAP) (25.8 vs. 17.5 U/liter) were higher, but height (162.3 vs. 167.7 cm) and 1,25-dihydroxyvitamin D (1,25D) (39.2 vs. 48.7 pg/ml) were lower in bariatric surgery patients than controls. There was no difference in serum sclerostin, amino-terminal collagen cross-links, 25-hydroxyvitamin D (25D), calcium, phosphate, and creatinine between groups. In the combined sample, leptin was positively related to PTH, FGF23, and BAP but not to 1,25D or sclerostin. Multiple regression analysis demonstrated that PTH was predicted by leptin and Ca (R(2) = 0.39); 1,25D by 25D, FGF23, and phosphate (R(2) = 0.43); FGF23 by leptin and 1,25D (R(2) = 0.27); BAP by leptin, PTH, and Ca (R(2) = 0.39); and sclerostin by leptin and PTH (R(2) = 0.20)., Conclusions: Women having bariatric surgery had higher leptin, PTH, FGF23, and BAP and lower 1,25D than controls. Leptin predicted the serum levels of PTH, 1,25D, and FGF23, the mineral-regulating hormones, and BAP, a bone formation marker, in women with body mass index ranging from 13.9-65.8 kg/m(2). The results suggest that leptin has an endocrine or paracrine effect on PTH and FGF23 production and that PTH may be one of the signals in obesity that leads to increased bone mass.

Context: Overweight adolescents have low bone mineral content for weight and are at increased risk for fractures., Objective: The aim was to determine whether overweight and obesity influence the positive relationship between dietary calcium intake and skeletal calcium retention in adolescents., Design: Analysis of pooled data from calcium balance studies in adolescents., Setting: Participants each underwent a 3-wk calcium balance study in a controlled environment., Participants: Participants included 280 White, Black, and Asian boys (n = 73) and girls (n = 207) ages 10-16 yr., Main Outcome Measure: The relationship among body mass index (BMI), calcium intake, and calcium retention was modeled using linear regression., Results: Calcium intake, BMI, sex, race, and age explained 27.9% of the variation in calcium retention. At low calcium intakes, there was no effect of BMI on skeletal calcium retention, but at higher calcium intakes, BMI increased skeletal calcium retention., Conclusions: Greater gains in calcium retention occur with increases in calcium intake in adolescents with higher BMI compared with those with lower BMI. Additional studies are needed to investigate whether increasing calcium intake reduces the increased risk of fracture associated with overweight and obesity in adolescents.

Context: The relationship between calcium (Ca) intake and Ca retention in adolescent boys was recently reported., Objective: This study evaluated the influence of Ca intake, serum hormone levels, biomarkers of bone metabolism, habitual physical activity, habitual Ca intake, and physical fitness on Ca retention in the same sample., Design: This study was a randomized, cross-over design that consisted of two 3-wk metabolic balance periods., Setting: The study took place on a university campus as a summer camp., Patients or Other Participants: A total of 31 American white boys (13-15 yr) participated in the study., Interventions: Each subject consumed a controlled diet with one of five high-low Ca intake pairs that ranged from 670-2003 mg/d, which was manipulated utilizing a fortified beverage., Main Outcome Measures: Ca retention was determined by Ca intake minus urinary and fecal Ca excretion during each balance period., Results: Ca intake explained 21.7% of the variability in Ca retention, and serum IGF-I concentration explained an additional 11.5%. Other serum hormone levels did not significantly add to the model. Biomarkers of bone metabolism, habitual physical activity, habitual Ca intake, and physical fitness were not significant predictors of Ca retention in adolescent boys., Conclusions: IGF-I, a regulator of growth during puberty, is an important predictor of Ca retention in adolescent boys. However, dietary Ca intake is an even greater predictor of Ca retention during this period of growth.