Plasma leptin concentrations are associated with bone mineral density and the presence of vertebral fractures in postmenopausal women

Longitudinal evaluation of serum leptin and bone mineral density in early postmenopausal women

OBJECTIVE

To evaluate total and site-specific bone mineral density (BMD) and serum leptin levels in postmenopausal women treated with a calcium supplement and in postmenopausal women receiving estrogen plus progestin therapy.

DESIGN

Forty-four women were randomized to receive either calcium supplementation (group A, n = 22) or transdermal 17beta-estradiol at a dose of 50 mug/day in a continuous regimen and nomegestrol at a dose of 5 mg/day for 12 days per month in a sequential regimen (group B, n = 22). All women underwent dual-energy x-ray absorptiometry determination of BMD and blood sampling in the morning at the beginning of the study and after 12 months. Leptin was determined by radioimmunoassay in all samples.

RESULTS

After 12 months, serum leptin levels were significantly higher in group A (control) in comparison with group B and baseline values, whereas both total and pelvic BMDs were significantly lower in group A in comparison with group B and baseline values. At baseline, a significant correlation was found between leptin levels, body mass index, and total-body BMD. After 12 months, leptin was still correlated to body mass index in both groups, but the association with BMD was lost.

CONCLUSIONS

This study confirms previous evidence of a significant correlation between serum leptin and BMD in early postmenopausal women. Furthermore, this correlation is lost over time during the progression of the postmenopausal period, independently from the administration of estrogen-progestin therapy. Further studies and longer follow-up periods are needed to better understand theses issues.

Serum leptin and adiponectin are positively associated with bone mineral density at the distal radius in patients with type 2 diabetes mellitus

There have been several reports about associations of serum leptin or adiponectin with bone mineral density and biochemical markers of bone turnover. However, the precise roles of adipocytokines in bone metabolism have not been fully elucidated. We investigated the associations of serum level of leptin or adiponectin with bone mineral density, serum osteocalcin, and urinary N-terminal telopeptide of type I collagen (NTX) in 40 Japanese patients with type 2 diabetes mellitus. Bone mineral density was measured by using dual-energy x-ray absorptiometry at different sites (distal radius, femoral neck, and lumbar spine) and was expressed as z score. Multiple regression analysis revealed that there were significant positive correlations between serum leptin or adiponectin level and z score at the distal radius, but not at the femoral neck or the lumbar spine. Although no correlation was observed between serum leptin and serum osteocalcin, there was a significant negative correlation between serum leptin and urinary NTX, a marker of bone resorption. No correlation was observed between serum adiponectin and serum osteocalcin or urinary NTX. These results indicate that leptin and adiponectin may have a protective effect on bone metabolism in patients with type 2 diabetes mellitus.

The new field of neuroskeletal biology

The fields of neuroscience and bone biology have recently converged following the discovery that bone remodeling is directly regulated by the brain. This work has defined bone remodeling as one of the cardinal physiological functions of the body, subject to homeostatic regulation and integrated with the other major physiological functions by the hypothalamus. Central to this discovery was the definition of the adipocyte-derived hormone leptin as a regulator of both arms of bone remodeling, formation and resorption, through its action on the ventromedial hypothalamus and subsequently via the sympathetic nervous system to osteoblasts. The characterization of the sympathetic nervous system as a regulator of bone remodeling has led to several large clinical studies demonstrating a substantial protective effect of beta-blockers, particularly beta1-blockers, on fracture risk. Studies in model organisms have reinforced the role of the central nervous system in the regulation of bone remodeling in vivo by the identification of several additional genes, namely cocaine and amphetamine regulated transcript (Cart), melanocortin 4 receptor (Mc4R), neuropeptide Y (NPY), Y2 receptor, cannabinoid receptor CB1 (Cnbr1), and the genes of the circadian clock. These genes have several common features, including high levels of expression in the hypothalamus and the ability to regulate other major physiological functions in addition to bone remodeling including energy homeostasis, body weight, and reproduction. We review the major pathways that define the new field of neuroskeletal biology and identify further avenues of inquiry.

The relationship between birth weight leptin and bone mineral status in newborn infants

BACKGROUND

The positive relationship between fat mass, bone mass and leptin has been shown in fetal mouse cartilage/bone. It has been shown that umbilical venous leptin predicts both the size of the neonatal skeleton and its estimated volumetric mineral density.

AIMS

This study investigates how birth weight and bone mineralization correlate with leptin levels. In addition, we aimed to determine the predictive value of anthropometrics measurements and gender on variability in bone mineral status.

METHODS

Umbilical cord venous blood samples were obtained at the delivery from 100 term newborn infants. Forty of the newborn infants had birth weights appropriate for gestational age (AGA), 30 were small for gestational age (SGA) and 30 were large for gestational age (LGA). Data were acquired using the whole body dual energy X-ray obsorptiometry scanner in the first 24 h after birth.

RESULTS

Leptin concentrations were higher in LGA (36.6 +/-12.0 ng/ml; p < 0.0001), but lower in SGA (11.7 +/- 5.6 ng/ml; p < 0.001) than in AGA infants (20.3 +/- 7.6 ng/ml). Whole body bone mineral density and whole body bone mineral content were higher in LGA babies (0.442 +/- 0.025 g/cm(2), 71.6 +/- 9.0 g, p < 0.01, p < 0.001, respectively) but lower in SGA (0.381 +/- 0.027 g/cm(2), 29.1 +/- 9.1 g, p < 0.001, p < 0.001, respectively) than in AGA babies (0.426 +/- 0.022 g/cm(2), 53.7 +/- 9.6 g, respectively). The percentage of whole body bone mineral content was lower in SGA (1.3 +/- 0.3) than in AGA (1.6 +/- 0.2, p < 0.001) and LGA (1.7 +/- 0.2, p < 0.001). In stepwise linear regression analyses models; leptin is not found related to the bone indices.

CONCLUSION

Our study does not provide support for the hypothesis that leptin may play a major role in the regulation of bone metabolism in the developing skeleton.

Fat mass is not beneficial to bone in adolescents and young adults

CONTEXT

Although muscle mass is beneficial to bone, studies on the effect of fat mass on bone have yielded conflicting results.

OBJECTIVE

The aim of this study was to assess the relations between lean and fat mass and bone structure.

DESIGN

This study was cross-sectional.

SETTING

The study was conducted in a general community.

SUBJECTS

Subjects included 300 healthy sexually mature adolescents and young adults (150 males and 150 females) between the ages of 13 and 21 yr.

MAIN OUTCOME MEASURE

We investigated the relation between dual-energy x-ray absorptiometry (DXA) measures of total body fat and lean mass and bone values obtained with DXA (legs and lumbar spine bone mineral density and bone mineral content) and computed tomography (CT) (cross-sectional and cortical bone areas of the femurs and cross-sectional area and cancellous bone density of the vertebrae).

RESULTS

Simple and multiple linear regression analyses showed significant positive relations between DXA lean mass and all CT and DXA measures of bone in the axial and appendicular skeletons (all P < 0.005). In contrast, whereas Pearson correlations between DXA measures of fat mass and bone parameters were generally positive, multiple regression analyses showed that fat mass, after accounting for lean mass, trunk height/leg length, had a negative, or no, correlation with CT and DXA values for bone.

CONCLUSIONS

Our findings provide compelling evidence that, despite increased mechanical loading and independent of lean mass, adipose tissue is not beneficial to bone structure.

Skeletal muscle mass, fat mass, and hip bone mineral density in elderly women with hip fracture

Soft tissue body composition strongly affects bone health. Our aim was to investigate the relationship between both skeletal muscle mass (SMM) and fat mass (FM) and femoral bone mineral density (BMD) in a sample of elderly women with hip fracture. We assessed 293 of 325 hip fracture women admitted consecutively to a rehabilitation hospital. Soft tissue body composition and BMD were assessed by dual-energy X-ray absorptiometry (DXA), 23.2 +/- 7.7 (mean +/- SD) days after fracture occurrence. BMD was measured at four sites (neck, total femur, trochanter, intertrochanteric area) in the unfractured femur. Appendicular lean mass (aLM) was calculated as the sum of LM in arms and legs. We used two approaches to adjust aLM for body size: aLM divided by height squared (aLM/ht(2)), and aLM adjusted for height and FM (residuals). Both FM and aLM were significantly correlated with femoral BMD. However, the correlation coefficients for aLM were lower than for FM; they further decreased after adjustment for height squared, and were no longer significant after correction for both height and FM (residuals). When FM, aLM/ht(2), age, and time spent between fracture occurrence and DXA assessment were included together as the independent variables in a regression model, FM was the only independent variable significantly associated with BMD. The coefficients of partial correlation ranged from 0.414 to 0.647 depending on the femoral region of BMD assessment (P < 0.001). FM, but not SMM emerged as a pivotal determinant of BMD in our sample of hip fracture women.

Osteoporosis in the elderly with chronic kidney disease

Considering the aging dialysis population of today, increasing our knowledge about the nature, diagnosis and the treatment of bone mineral density (BMD) problems in end-stage renal disease (ESRD) patients deserves more attention. Osteoporosis is basicly defined as a decrease in bone mass. Large epidemiological studies in general population have identified several risk factors for osteoporosis including advancing age, female gender, white race, decreased calcium intake, gastric acid suppression therapy, sedentary lifestyle, premature loss of gonadal function, decreased estrogen secretion, thin body habitus, decreased physical activity, cigarette smoking, alcohol abuse, excess glucocorticoid exposure, and possibly some genetic factors. Osteoporosis in ESRD patients is only a part of a wider spectrum of metabolic bone problems, namely uremic osteodystrophy. Therefore, its diagnosis, management and follow-up may differ from the general population and an individualization of diagnosis and definition for dialysis population may be necessary. However, standard diagnostic tools such as dual energy X-ray absorptiometry (DEXA) have been widely used for the assessment of bone mineral deficiency status in ESRD patients. Regardless of the methods, most of the studies are in concordance with a reduced BMD in HD and PD patients. Dialysis patients are known to be at increased risk for low-trauma fractures. Thinning of cortical bone, which is responsible for the largest contribution toward reduced bone mineral content in chronic renal failure results in increased fracture risk. In either normal population and dialysis patients, fracture risk is increased with age. But in dialysis patients, besides age, several other factors may also affect the degree of bone mineral deficiency, and age-BMD relationship may be blunted. Female sex, in hemodialysis patients is negatively associated with total hip BMD. While several studies have been unable to demonstrate any association between BMD and PTH levels, larger body size has been shown to have a significant positive effect on BMD in both hemodialysis and peritoneal dialysis patients. Although they have been used in small groups of chronic kidney disease (CKD) and ESRD patients, because of their potential nephrotoxicity and hypocalcemic effects, use of biphosphonates in renal patients is questionable. Currently, bone biopsy, in order to exclude adynamic bone disease is recommended before beginning treatment with bisphosphonates in chronic kidney disease and dialysis patients.

Bone density and markers of bone remodeling in type 1 male diabetic patients

AIMS

To assess the prevalence and severity of bone disease in type 1 diabetic patients and to determine serum markers of bone remodeling as well as their relationship with bone mineral density (BMD).

METHODS

BMD [by dual energy x-ray absorptiometry (DXA)] and serum markers of bone remodeling [osteocalcin, c-terminal telopeptide of type I collagen (CTX)], leptin and osteoprotegerin (OPG) were measured in 42 adult males with type 1 diabetes. Twenty-four non-diabetic subjects served as controls.

RESULTS

In 40% of the patients, osteopenia at the lumbar spine (L1-L4) and/or at the left hip was found, and 7% met criteria for osteoporosis. L1-L4 BMD z-score was correlated with age (r=0.365, P=0.018) and a similar trend was observed at left hip. L1-L4 BMD z-score was negatively correlated with CTX and osteocalcin (r=-0.343, P=0.028; r=-0.376, P=0.024, respectively). A significant correlation was evidenced between BMD z-score at both lumbar spine and left hip and leptin values (r=0.343, P=0.03; r=0.395, P=0.012, respectively) but after adjustment for weight this correlation was no longer significant. Osteocalcin, CTX and leptin concentrations were comparable between patients and controls, while OPG concentrations tend to be higher in diabetic subjects (P=0.08). CTX was negatively correlated with age (r=-0.390, P=0.012) and positively correlated with osteocalcin (r=0.696, P<0.001). OPG was positively correlated with age (r=0.507, P=0.001).

CONCLUSION

Our results suggest that in diabetic subjects osteopenia is a relatively frequent complication but bone loss is attenuated with age progression. Whether this is also mediated by OPG and/or leptin remains to be confirmed.

Leptin predicts BMD and bone resorption in older women but not older men: the Rancho Bernardo study

We studied the relation of leptin to bone, bone loss, and bone turnover in community-dwelling men and women. Leptin predicted higher BMD and lower bone turnover only in women. Leptin was not associated with 4-year bone loss in either sex.

INTRODUCTION

Leptin, the protein product of the obesity (OB) gene produced in fat tissue, was originally thought to be involved only in the regulation of food intake and energy balance. Recent evidence suggests that leptin may play a role in the pathophysiology of several chronic diseases. Studies of the association between leptin and bone have been numerous yet inconclusive. Only one previous longitudinal study has been reported, which showed no association of leptin with BMD after adjusting for body size.

MATERIALS AND METHODS

We report the association of serum leptin with BMD at the hip, spine, and midshaft radius in community-dwelling men (n = 498) and nonestrogen-using postmenopausal women (n = 411) 45-92 years of age. Serum leptin was measured in blood obtained between 1984 and 1987. Between 1988 and 1991, BMD was measured at the midshaft radius by single photon absorptiometry and at the femoral neck, total hip, and lumbar spine by DXA; at the same visit, height, weight, and body fat (by bioelectrical impedance analysis) were measured, and bone resorption was assessed in a subset of men (n = 286) and women (n = 241) using urine N-telopeptide (NTX). Four years later, axial BMD was remeasured in 536 participants. Sex-specific associations of leptin with BMD, NTX, and bone loss were tested using regression analysis.

RESULTS

In unadjusted analyses, leptin was associated with BMD at the femoral neck, total hip, lumbar spine, and midshaft radius in both sexes (p < 0.01). In multiple regression analyses, adjusted for age, BMI, and other bone-related factors, only women showed a graded stepwise positive association between serum leptin and BMD at all sites and a negative stepwise association with NTX (all p for trend < 0.01). Baseline leptin levels did not predict 4-year bone loss in either sex.

CONCLUSIONS

A favorable dose-dependent leptin-BMD association unexplained by obesity was observed only in women. The reason for the sex difference is unknown.

Parathyroid hormone and leptin--new peptides, expanding clinical prospects

There are three injectable and one oral bone-building (i.e., bone anabolic) parathyroid hormone (PTH) peptides. One of the four, Lilly's injectable teriparatide (Forteo), is currently being used, and the other three are in clinical trials. They are being used or assessed only for treating postmenopausal osteoporosis. However, their potential clinical targets now extend far beyond osteoporosis. They can accelerate the mending of even severe non-union fractures; they will probably be used to strengthen the anchorage of pros-theses to bone; they have been shown to treat psoriasis that has resisted other treatments; they can increase the size of haematopoietic stem cell proliferation and accelerate the endogenous repopulation or repopulation by donor transplants of bone marrow depleted by chemotherapeutic drugs; and they may prevent vascular ossification. Leptin, a member of the cytokine superfamily has a PTH-like osteogenic activity and may even partly mediate PTH action. But leptin has two drawbacks that cloud its therapeutic future. First, apart from directly stimulating osteoblastic cells, it targets cells in the hypothalamic ventromedial nuclei and through them it reduces oestrogenic activity by promoting osteoblast-suppressing adrenergic activity. Second, it stimulates vascular and heart valve ossification, which leads to such events as heart failure and diabetic limb amputations.

Leptin and its emerging role in children and adolescents

Leptin is an adipocyte-secreted hormone which plays a key role in energy homeostasis. Recent “proof of concept” studies involving leptin administration to humans support its critical role in regulating energy homeostasis, neuroendocrine and immune function as well as insulin resistance in states of energy/ caloric deprivation. Moreover, interventional studies in leptin deficient children and observational studies in normal girls and boys support a role for leptin as a permissive factor for the initiation of puberty in children. The potential clinical usefulness of leptin in several disease states in children and adolescents, including hypothalamic amenorrhea, eating disorders and syndromes of insulin resistance is still under investigation.

Maintenance of muscle strength may counteract weight-loss-related postmenopausal bone loss--a population-based approach

INTRODUCTION

Weight loss significantly increases postmenopausal bone loss, but the effects of muscle strength change on weight-loss-associated bone loss remain unclear. The study population, 587 peri- and postmenopausal women, was a random sample of the original Osteoporosis Risk Factor and Prevention Study (OSTPRE) study cohort (n=14,220) in Kuopio, Finland. Bone mineral density (BMD) at the lumbar spine (LS) and femoral neck (FN) was measured with dual x-ray absorptiometry, and grip strength was measured with a pneumatic squeeze dynamometer at baseline in 1989-1991 and at the 10-year follow-up in 1999-2001.

METHODS

Women were divided into three groups according to change in age-grouped grip-strength quartile in both of the measurements: "decreased" (n=133), "maintained" (n=300), and "improved" (n=154). In addition, the study sample was divided into two groups according to weight change during the follow-up: weight losers (n=156) and weight gainers (n=431).

RESULTS

There were no differences in the change status of grip (muscle) strength between the weight loss and weight gain groups (p>0.500, Pearson chi-square test). Women losing weight during the follow-up and within the improved grip-strength-change group had a significantly lower bone loss rate compared with those in the maintained and decreased grip-strength-change groups (p<0.01 in comparison to the decreased group). This was in contrast to women who gained weight during the follow-up (not significant between any grip-strength-change groups). Furthermore, women who lost body weight and were in the improved grip-strength-change group had a bone loss rate comparable with that of the women who gained body weight (not significant). This was in contrast to the maintained (p<0.05 between weight losers versus gainers in LS) and decreased grip-strength-change groups (p<0.01 weight losers versus gainers in LS and FN).

CONCLUSION

The present study suggests that maintaining muscle strength may counteract postmenopausal bone loss related to weight loss. Accordingly, exercise that improves muscle strength may be encouraged for postmenopausal women with weight loss intentions for other health reasons.

Relation of body composition, fat mass, and serum lipids to osteoporotic fractures and bone mineral density in Chinese men and women

BACKGROUND

Higher fat mass may be an independent risk factor for osteoporosis and osteoporotic fractures.

OBJECTIVE

We aimed to determine the independent contribution of fat mass to osteoporosis and to estimate the risk of osteoporotic fractures in relation to body weight, lean mass, and other confounders.

DESIGN

This was a community-based, cross-sectional study of 7137 men, 4585 premenopausal women, and 2248 postmenopausal women aged 25-64 y. Total-body and hip bone mineral content (BMC) and bone mineral density (BMD) and body composition were measured by dual-energy X-ray absorptiometry. Serum lipids were measured. Sex- and menopause-specific multiple generalized linear models were applied.

RESULTS

Across 5-kg strata of body weight, fat mass was significantly inversely associated with BMC in the whole body and total hip. When we compared the highest quartile with the lowest quartile of percentage fat mass in men, premenopausal women, and postmenopausal women, the adjusted odds ratios (95% CIs) of osteoporosis defined by hip BMD were 5.2 (2.1, 13.2), 5.0 (1.7, 15.1), and 6.9 (4.3, 11.2), respectively. Significant linear trends existed for higher risks of osteoporosis, osteopenia, and nonspine fractures with higher percentage fat mass. Significant negative relations were found between whole-body BMC and cholesterol, triacylglycerol, LDL, and the ratio of HDL to LDL in all groups.

CONCLUSIONS

Risks of osteoporosis, osteopenia, and nonspine fractures were significantly higher for subjects with higher percentage body fat independent of body weight, physical activity, and age. Thus, fat mass has a negative effect on bone mass in contrast with the positive effect of weight-bearing itself.

Body composition and vertebral fracture risk in female patients treated with glucocorticoid

INTRODUCTION

Glucocorticoid (GC) causes bone loss and an increase in bone fragility. However, fracture risk was found to be only partly explained by bone mineral density in GC-treated patients (GC patients). Although GC causes a change in the distribution of fat in the body, the relationship between body composition and fracture risk in GC patients remains unknown.

METHODS

The present study examined the relationship between the presence or absence of vertebral fractures and various indices, including body composition, in 92 premenopausal GC patients, 122 postmenopausal GC patients and 122 postmenopausal age-matched control subjects. Dual-energy X-ray absorptiometry was employed to analyze body composition.

RESULTS

Percentage lean body mass (LBM), % fat and % trunk fat were not significantly different between postmenopausal GC patients and the control women. When groups with and without vertebral fractures were compared, % LBM and % fat were significantly higher and lower in groups with vertebral fractures, respectively, in postmenopausal GC patients, but not in the postmenopausal control women, although % trunk fat was not significantly different between groups with and without vertebral fractures. Femoral neck BMD was negatively correlated with % LBM and positively correlated with % fat. In premenopausal GC patients, % trunk fat was significantly higher in the fracture group, although % LBM and % fat were not significantly different between groups with and without vertebral fractures.

CONCLUSION

The present study revealed that body composition is related to vertebral fracture risk in GC-treated patients. Lower % fat can be included in the determination of vertebral fractures in postmenopausal GC-treated patients. The influence of body composition on vertebral fracture risk may be different between the pre- and postmenopausal state in GC patients.

Physical activity in the prevention and amelioration of osteoporosis in women : interaction of mechanical, hormonal and dietary factors

Osteoporosis is a serious health problem that diminishes quality of life and levies a financial burden on those who fear and experience bone fractures. Physical activity as a way to prevent osteoporosis is based on evidence that it can regulate bone maintenance and stimulate bone formation including the accumulation of mineral, in addition to strengthening muscles, improving balance, and thus reducing the overall risk of falls and fractures. Currently, our understanding of how to use exercise effectively in the prevention of osteoporosis is incomplete. It is uncertain whether exercise will help accumulate more overall peak bone mass during childhood, adolescence and young adulthood. Also, the consistent effectiveness of exercise to increase bone mass, or at least arrest the loss of bone mass after menopause, is also in question. Within this framework, section 1 introduces mechanical characteristics of bones to assist the reader in understanding their responses to physical activity. Section 2 reviews hormonal, nutritional and mechanical factors necessary for the growth of bones in length, width and mineral content that produce peak bone mass in the course of childhood and adolescence using a large sample of healthy Caucasian girls and female adolescents for reference. Effectiveness of exercise is evaluated throughout using absolute changes in bone with the underlying assumption that useful exercise should produce changes that approximate or exceed the absolute magnitude of bone parameters in a healthy reference population. Physical activity increases growth in width and mineral content of bones in girls and adolescent females, particularly when it is initiated before puberty, carried out in volumes and at intensities seen in athletes, and accompanied by adequate caloric and calcium intakes. Similar increases are seen in young women following the termination of statural growth in response to athletic training, but not to more limited levels of physical activity characteristic of longitudinal training studies. After 9-12 months of regular exercise, young adult women often show very small benefits to bone health, possibly because of large subject attrition rates, inadequate exercise intensity, duration or frequency, or because at this stage of life accumulation of bone mass may be at its natural peak. The important influence of hormones as well as dietary and specific nutrient abundance on bone growth and health are emphasised, and premature bone loss associated with dietary restriction and estradiol withdrawal in exercise-induced amenorrhoea is described. In section 3, the same assessment is applied to the effects of physical activity in postmenopausal women. Studies of postmenopausal women are presented from the perspective of limitations of the capacity of the skeleton to adapt to mechanical stress of exercise due to altered hormonal status and inadequate intake of specific nutrients. After menopause, effectiveness of exercise to increase bone mineral depends heavily on adequate availability of dietary calcium. Relatively infrequent evidence that physical activity prevents bone loss or increases bone mineral after menopause may be a consequence of inadequate calcium availability or low intensity of exercise in training studies. Several studies with postmenopausal women show modest increases in bone mineral toward the norm seen in a healthy population in response to high-intensity training. Physical activities continue to stimulate increases in bone diameter throughout the lifespan. These exercise-stimulated increases in bone diameter diminish the risk of fractures by mechanically counteracting the thinning of bones and increases in bone porosity. Seven principles of bone adaptation to mechanical stress are reviewed in section 4 to suggest how exercise by human subjects could be made more effective. They posit that exercise should: (i) be dynamic, not static; (ii) exceed a threshold intensity; (iii) exceed a threshold strain frequency; (iv) be relatively brief but intermittent; (v) impose an unusual loading pattern on the bones; (vi) be supported by unlimited nutrient energy; and (vii) include adequate calcium and cholecalciferol (vitamin D3) availability.

Raloxifene increases serum leptin levels in postmenopausal women: a prospective study

OBJECTIVE

The purpose of this study was to investigate the effect of raloxifene on leptin and insulin-like growth factor-I levels and their relation with the biochemical markers of bone metabolism in postmenopausal women.

STUDY DESIGN

Sixty-four women were given 60 mg/d raloxifene for 6 months. Serum leptin, insulin-like growth factor-I, alkaline phosphatase, calcium, osteocalcin, and collagen type I cross-link C-telopeptide levels were measured before and after the treatment. The patients were grouped as obese (body mass index, > or =25 kg/m2) or non-obese (body mass index, <25 kg/m2).

RESULTS

The mean basal leptin level was significantly higher (P < .001), and the mean cross-link C-telopeptide level was significantly lower (P = .001) in obese patients. Raloxifene therapy increased leptin levels (P < .001) and decreased insulin-like growth factor-I, alkaline phosphatase, and cross-link C-telopeptide levels significantly (P < .001). There was a strong negative correlation between leptin and cross-link C-telopeptide (r = -0.703; P < .001). Insulin-like growth factor-I was not correlated with any parameter.

CONCLUSION

Raloxifene increases serum leptin levels while decreasing bone resorption in postmenopausal women.

The relationship between serum resistin, leptin, adiponectin, ghrelin levels and bone mineral density in middle-aged men

OBJECTIVE

Body weight is a significant predictor of bone mass. Hormonal factors such as sex hormones, insulin, leptin and adiponectin are thought to play a role in the mechanisms controlling the association of body weight and fat mass with bone mass. However, contradictory results have been reported for the association between serum adipocytokines and bone mineral density (BMD). We therefore examined whether the serum adipocytokine and ghrelin levels, markers of fat metabolism, are associated with BMD in male adults.

PATIENTS AND MEASUREMENTS

For 80 male adults (average age 54.5 +/- 6.4 years; average body mass index (BMI) 24.4 +/- 2.5 kg/m2), the correlations between serum resistin, leptin, adiponectin and ghrelin levels with BMD were investigated.

RESULTS

Among the adipocytokines, serum resistin levels were negatively correlated with lumbar spine BMD (r = -0.237, P = 0.05). After adjustment was made for age and BMI, log-transformed serum leptin showed a significant negative correlation with lumbar spine BMD, which was not seen on bivariate analysis (r = -0.237, P = 0.039). Femoral neck BMD was marginally associated only with serum adiponectin levels (r = -0.226, P = 0.062). In multiple regression analyses, among the adipokines, only resistin was a significant determinant of lumbar spine BMD, although the variance was small (R2 = 0.256). Serum ghrelin levels were not correlated with the BMD of either body site.

CONCLUSIONS

Serum resistin level showed a significant negative correlation with lumbar spine BMD, although the variance was small. Further studies are needed to elucidate the role of adipocytokines in bone metabolism.

Role of leptin in energy-deprivation states: normal human physiology and clinical implications for hypothalamic amenorrhoea and anorexia nervosa

Leptin is an adipocyte-secreted hormone that plays a key part in energy homoeostasis. Advances in leptin physiology have established that the main role of this hormone is to signal energy availability in energy-deficient states. Studies in animals and human beings have shown that low concentrations of leptin are fully or partly responsible for starvation-induced changes in neuroendocrine axes, including low reproductive, thyroid, and insulin-like growth factor (IGF) hormones. Disease states such as exercise-induced hypothalamic amenorrhoea and anorexia nervosa are also associated with low concentrations of leptin and a similar spectrum of neuroendocrine abnormalities. We have recently shown in an interventional, proof-of-concept study that leptin can restore ovulatory menstrual cycles and improve reproductive, thyroid, and IGF hormones and bone markers in hypothalamic amenorrhoea. Further studies are warranted to establish the safety and effectiveness of leptin for the infertility and osteoporosis associated with hypothalamic amenorrhoea, and to clarify its role in anorexia nervosa.

Relationship of serum leptin with age, body weight, body mass index, and bone mineral density in healthy mainland Chinese women

BACKGROUND

Serum leptin concentration is associated with age, fat and bone mineral density (BMD), and there are ethnic differences in physique and BMD values. The relationship between serum leptin concentration and BMD in Chinese women is presently unknown. We examined the relationship of serum leptin concentration with age, body weight, BMI and BMD in mainland Chinese women.

METHODS

Serum leptin concentration in a population of 676 Chinese females, aged 20-80 years (45.4+/-14.8 years, mean+/-S.D.), was measured using an enzyme-linked immunosorbent assay (ELISA). BMD values were measured by dual-energy X-ray absorptiometry (DXA) at a number of sites: the posteroanterior lumbar spine (PA, L1-L4), lateral lumbar spine (Lat, L2-L4), hip (including the femoral neck (FN) and total hip (T-hip)), and forearm (one-third region (RU1/3) and total region (RUT)). The relationship between changes in serum leptin concentration with age, body weight, height, body mass index (BMI) and BMD values at six sites were analyzed using 10 different regression models, and the models giving the best fit were selected.

RESULTS

The cubic regression model best described the changes in serum leptin concentration with age (R(2)=0.048, p<0.001) and body weight (R(2)=0.352, p<0.001), while the quadratic regression model was best for serum leptin concentration changes with BMI (R(2)=0.410, p<0.001); serum leptin concentration was not correlated with height. Serum leptin concentration was significantly higher in postmenopausal than premenopausal women (p<0.001). Serum leptin concentration was correlated with Lat BMD (R(2)=0.012, p<0.018), FN BMD (R(2)=0.006, p<0.041) and T-hip BMD (R(2)=0.013, p<0.004) in the whole population. In premenopausal women, leptin was positively associated with BMD except for Lat (R(2)=0.029-0.055, p<0.008); in postmenopausal women, leptin was also positively associated with AP, FN, T-hip BMD (R(2)=0.026-0.042, p<0.007). However, after adjusting for BMI not for body weight, there was no association between serum leptin concentration and age. Meanwhile, after adjustment for age, body weight and BMI, there was no association between serum leptin concentration and BMD values in premenopausal and postmenopausal women.

CONCLUSIONS

Age-related changes in serum leptin concentration is dependent on BMI, but not a direct determinant of BMD in Chinese females.

Plasma leptin concentrations in postmenopausal women with osteoporosis

Osteoporosis is less common in obese individuals with increased bone mineral density (BMD) and plasma leptin concentrations. The aim of this study was to determine the correlation between leptin levels and BMD in postmenopausal women. The study consisted of 90 postmenopausal women with a mean age of 53.45 +/- 0.87 years who visited our outpatient clinic for the evaluation of BMD. Thirty-six post-menopausal women with osteoporosis (mean age: 54.52 +/- 1.41 years and mean body mass index (BMI, kg/m2) 29.33 +/- 0.66), 30 age- and BMI-matched postmenopausal women with normal BMD, and 24 postmenopausal women (mean age: 52.79 +/- 1.48 years and mean BMI: 29.45 +/- 0.89) with osteopenic BMD were included in the study. Plasma concentrations of leptin after an overnight fast were measured by radioimmunoassay. BMD values were measured by dual-energy X-ray absorptiometry (DEXA) at the L2-L4 lumbar spine and femoral neck. The median spine BMD value in the patient group (0.67 +/- 0.08 g/cm2, mean +/- SEM) was significantly lower than that in the control group (1.02 +/- 0.25 g/cm2, mean +/- SEM) and osteopenic group (0.87 +/- 0.05 g/cm2, mean +/- SEM) (p < 0.005). The mean spine BMD value (T score -3.63 +/- 0.25, mean +/- SEM) and the mean femur neck BMD value (T score -2.55 +/- 0.18, mean +/- SEM) of the osteoporosis group were significantly lower than that in the normal BMD group (+ 0.33 +/- 0.14 and + 0.27 +/- 0.18, P < 0.001) and in the osteopenia group (-1.74 +/- 0,1 and -1.18 +/- 0.05, p < 0.005). The mean plasma leptin concentration in the osteoporotic group (17.03 +/- 1.40 ng/ml) was not significantly different from that in the normal BMD group and the osteopenia group (16.55 +/- 1.50 ng/ml; 16.16 +/- 1.60, respectively, p > 0.150). Plasma leptin concentrations were correlated with BMI in three groups (r(s) = 0.450, p = 0.025 in normal BMD group and r(s) = 0.4254, P = 0.009 in the osteoporotic group, and r(s) = 395, p = 0.015 in the osteopenia group. There was no correlation between plasma leptin concentrations and BMD values in three groups (r(s) = -0.89 in normal BMD group, r(s) = -0.124 in osteopenia group, and r(s) = -0.195 in osteoporosis group). From this study we conclude that circulating plasma leptin does not have a significant direct influence on bone mass in postmenopausal women.

Blood leptin and adiponectin as possible mediators of the relation between fat mass and BMD in perimenopausal women

Fat mass is a predictor of BMD; however, the mechanisms involved remain uncertain. Two adipokines, leptin and adiponectin, were examined as potential mediators of this relation in 80 perimenopausal women. Adiponectin did not exert any effect on BMD, whereas leptin exerted a negative one, with insulin acting as a confounder to this relation.

INTRODUCTION

Fat mass is an important determinant of bone density, but the mechanism involved in this relation is uncertain. Leptin and adiponectin, as circulating peptides of adipocyte origin, are potential contributors to this relation. We investigated the role of leptin and adiponectin in mediating fat mass effects on the skeleton of perimenopausal women.

MATERIALS AND METHODS

Twenty-five premenopausal and 55 postmenopausal, healthy women (42-68 years old) participated in our study. Lumbar spine BMD (BMD(L2-L4)) and total body BMC (TBBMC) were measured with DXA, leptin levels with ELISA, and adiponectin levels with radioimmunoassay (RIA). Additionally, body composition analysis was performed, as well as measurements of several hormones.

RESULTS

It was shown that serum leptin levels were negatively correlated with BMD (beta = -0.005, p = 0.027) and TBBMC (beta = -14.32, p = 0.013). The above correlation was observed only when serum insulin levels were included, as an independent variable, in the regression analysis model. Adiponectin was not significantly correlated with BMD(L2-L4) nor with TBBMC, either in the presence or absence of insulin.

CONCLUSION

Circulating adiponectin does not seem to exert any effect on bone mass. In contrast, circulating leptin showed a negative correlation with bone mass, dependent on serum insulin levels.

Fat body mass, leptin and femur bone mineral density in hip-fractured women

Fat body mass (FBM) is a strong predictor of both bone mineral density (BMD) and risk of hip fracture, but the mechanisms responsible are not completely understood. We addressed whether leptin is the link between FBM and BMD in hip-fractured women. Sixty-two of 74 women with hip fractures were evaluated. Serum leptin was measured by radioimmunoassay, 23.4+/-9.1 days (mean+/-SD) after fracture occurrence. BMD and body composition were assessed by dual-energy X-ray absorptiometry (DXA). As expected, a positive linear correlation was found between FBM and both leptin (r=0.782; p<0.001) and femur BMD measured at five sites (r value ranging from 0.293 to 0.498 depending on the site of the femur BMD assessment, p<0.05). A positive correlation between leptin and BMD measured at the intertrochanteric area (r=0.259; p<0.05) but not at the other four sites was shown. At linear multiple regression [dependent variable = femur BMD; independent variables = age, weight, height, body mass index, fracture type, term fracture-DXA, Barthel index score, FBM, lean body mass, serum PTH, serum 25(OH)vitamin D and leptin], FBM was positively associated with BMD measured at all the five sites. The association between leptin and BMD was inverse and it was significant at four of the five sites of the BMD assessment. In conclusion, in a sample of hip-fractured women, the positive association between FBM and femur BMD was not explained by serum leptin. On the contrary, after adjustment for FBM and other confounding variables, an inverse association between leptin and BMD was found.

Leptin and bone mineral density: a cross-sectional study in obese and nonobese men

Leptin has been suggested to decrease bone mineral density (BMD). This observational analysis explored the relationship between serum leptin and BMD in 327 nonobese men (controls) (body mass index 26.1 +/- 3.7 kg/m(2), age 49.9 +/- 6.0 yr) and 285 juvenile obese men (body mass index 35.9 +/- 5.9 kg/m(2), age 47.5 +/- 5.1 yr). Whole-body dual-energy x-ray absorptiometry scan measured BMD, fat mass, and lean mass. Fasting serum leptin (nanograms per milliliter) was strongly associated with fat mass (kilograms) in both controls (r = 0.876; P < 0.01) and juvenile obese (r = 0.838; P < 0.001). An inverse relation between BMD adjusted for body weight and serum leptin emerged in both the control group (r = -0.186; P < 0.01) and the juvenile obese group (r = -0.135; P < 0.05). In a multiple linear regression, fat mass, lean body mass, and occupational physical activity were positively associated with BMD in the control group, whereas in the juvenile obese, only lean body mass was positively associated with BMD and smoking negatively associated with BMD. Our study supports that leptin is inversely associated with BMD and may play a direct role in the bone metabolism in nonobese and obese Danish males, but it also stresses the fact that the strong covariation between the examined variables is a shortcoming of the cross-sectional design.

Serum leptin as a determinant of bone resorption in healthy postmenopausal women

To examine the relationships between serum leptin and bone metabolism, we measured bone mineral density (BMD) at the spine and the hip, fasting serum leptin, and osteocalcin and urinary excretion of C-terminal crosslinking telopeptide of type I collagen (CTX), as markers of bone formation and resorption, respectively, in 121 postmenopausal women aged 54 +/- 5 years. These parameters were also assessed at 6 months and 2 years of treatment with either 2.5 mg tibolone (n = 34), 1.25 mg tibolone (n = 45), or 2 mg estradiol plus 1 mg norethindrone acetate (n = 42). At baseline, serum leptin correlated positively with spine (r = 0.21, P = 0.02) and total hip (r = 0.26, P = 0.0044) BMD and negatively with CTX (r = -0.38, P < 0.0001) and osteocalcin (r = 0.21, P = 0.025). After adjustment for BMI and for fat mass, the association between serum leptin and CTX persisted with a partial correlation coefficient of -0.18 (P = 0.046) and of -0.22 (P = 0.03), respectively. Women in the highest quartile of leptin levels had 11% higher total hip (P = 0.0039) and lumbar spine BMD (P = 0.016), 21% lower osteocalcin (P = 0.01), and 38% lower CTX (P = 0.0005) than women in the lowest quartile (P < 0.05). During treatment, serum leptin levels increased (+14.7 +/- 47.3%, P = 0.019), without significant difference between the groups. This increase correlated with the increase in body weight (r = 0.46, P < 10(-4)). No correlation was found between the changes in leptin and the changes in bone parameters. In conclusion, leptin may play a role as a determinant of bone resorption in healthy, untreated postmenopausal women, but the effect of estradiol or tibolone on bone are not mediated by leptin.

Leptin, ghrelin, and proinflammatory cytokines: compounds with nutritional impact in chronic kidney disease?

Metabolic and nutritional derangements are prominent features of the uremic syndrome. Recent evidence suggest that several large-molecular-weight molecules that often are elevated in uremia, such as leptin, ghrelin, and proinflammatory cytokines, may have nutritional impact in this patient group. On the basis of present knowledge, these compounds could be regarded as suspected but not established uremic toxins. The discovery of the ob gene, its product leptin, and cerebral leptin receptors has undoubtedly widened our understanding of obesity and the underlying molecular and physiologic mechanisms that regulate food intake and body weight. Moreover, the recent discovery of leptin receptor isoforms in several peripheral organs suggests that leptin besides having a central function also has several important peripheral biological functions. Because uremic patients in general have an inappropriate elevation of circulatory leptin, further research is necessary to determine the potential biological effects of elevated leptin levels in end-stage renal disease. Also, because many symptoms and findings prevalent in the uremic syndrome are known to be associated with elevated levels of proinflammatory cytokines, such as interleukin-6, future studies are needed to evaluate the role of specific anti-inflammatory treatment strategies in malnourished uremic patients.

Determinants of bone density in 30- to 65-year-old women: a co-twin study

Reported effects of body composition and lifestyle on bone mineral density in pre-elderly adult women have been inconsistent. In a co-twin study, we measured bone mineral density, lean and fat mass, and lifestyle factors. Analyzing within pair differences, we found negative associations between bone mineral density and tobacco use (2.3-3.3% per 10 pack-years) and positive associations with sporting activity and lean and fat mass.

INTRODUCTION

Reported effects of body composition and lifestyle of bone mineral density in pre-elderly adult women have been inconsistent.

METHODS

In a co-twin study of 146 female twin pairs aged 30 to 65 years, DXA was used to measure bone mineral density at the lumbar spine, total hip, and forearm, total body bone mineral content, and lean and fat mass. Height and weight were measured. Menopausal status, dietary calcium intake, physical activity, current tobacco use, and alcohol consumption were determined by questionnaire. Within-pair differences in bone measures were regressed through the origin against within-pair differences in putative determinants.

RESULTS

Lean mass and fat mass were associated with greater bone mass at all sites. A discordance of 10 pack-years smoking was related to a 2.3-3.3% (SE, 0.8-1.0) decrease in bone density at all sites except the forearm, with the effects more evident in postmenopausal women. In all women, a 0.8% (SE, 0.3) difference in hip bone mineral density was associated with each hour per week difference in sporting activity, with effects more evident in premenopausal women. Daily dietary calcium intake was related to total body bone mineral content and forearm bone mineral density (1.4 +/- 0.7% increase for every 1000 mg). Lifetime alcohol consumption and walking were not consistently related to bone mass.

CONCLUSION

Several lifestyle and dietary factors, in particular tobacco use, were related to bone mineral density. Effect sizes varied by site. Characterization of determinants of bone mineral density in midlife and thereafter may lead to interventions that could minimize postmenopausal bone loss and reduce osteoporotic fracture risk.

Relationship between leptin levels and bone mineral density in the elderly

OBJECTIVE

To assess the relationship between circulating leptin levels, bone mineral content and density in the elderly.

DESIGN

A cross-sectional study.

PATIENTS

A cohort of 92 men and 171 women, with ages ranging from 68 to 75 years, selected as a healthy and normal functioning group, in the city centre of Verona.

MEASUREMENTS

Plasma leptin levels were determined in each participant. Body composition was evaluated with dual energy X-ray absorptiometry (DXA). Bone mineral content (BMC) and bone mineral density (BMD) were measured at whole-body, hip and femoral neck level in all subjects.

RESULTS

In both men and women a significant relationship between fat mass and whole-body BMC or BMD was found. The strength of this association was consistently reduced after adjustment for plasma leptin. A significant association between circulating leptin levels, whole-body, total hip and femoral neck BMC and BMD was found in both sexes. This association retained the statistical significance after adjustment for fat mass percentage, especially in women. In stepwise multiple linear regression analyses, leptin was shown to be a significant predictor of whole-body, total hip and femoral neck BMC and BMD, independently of age and the percentage of body fat in both sexes. The circulating levels of leptin accounted for a variance in whole-body BMC of 8.9% in men and 18.2% in women, and in whole-body BMD of 10.6% in women.

CONCLUSION

Our data show a significant relationship between leptin, bone mineral mass and density in healthy elderly men and women.

Effect of weight change on bone mass in female adolescents

The purpose of this study was to examine changes in bone mineral density/bone mineral content (BMD/BMC) in obese female adolescents (Tanner stages 2 to 4) pursuing a weight reduction program. This was a prospective pilot clinical investigation involving 92 obese females screened to meet inclusion criteria and required to participate in a 6-month weight loss intervention. Baseline, 6 months, and 12 months measurements were taken for total body/lumbar spine BMD/BMC and percentage body fat. Survey instrumentation included the following: calcium food frequency/24-hour dietary recall, physical activity, and psychological assessments for anxiety/self-esteem. Changes in bone measurements were compared with changes in body weight measurements using multiple linear regression. Other potentially confounding variables analyzed included bone area, calcium intake, baseline Tanner stage, activity level, and height. Total body/lumbar spine BMD/BMC changes were found to be most significantly correlated with weight changes in the subject population. Although mean weight increased, the rate of increase per a given height velocity slowed to an appropriate height for weight ratio. Individuals who lost weight did not lose BMD/BMC; however, the rate of growth declined when compared with all study subjects whose bone growth rate was consistent with normal weight female adolescents. In this study, weight changes were strongly related to bone measurement changes in an obese adolescent female population. Dietitians counseling obese young girls are encouraged to emphasize the importance of a healthy weight loss program with optimal calcium intake and inclusive of weight-bearing exercises.

Effect of subcutaneous leptin replacement therapy on bone metabolism in patients with generalized lipodystrophy

The adipocyte-derived hormone leptin, which plays an important role in energy homeostasis, has been suggested to have an influence on bone development and remodeling. However, it is not clear from animal studies whether leptin is a stimulator or an inhibitor of bone growth. Cross-sectional studies in humans suggest that serum leptin levels are positively associated with bone mineral density (BMD), but these observations are not consistent, and whether this relationship is independent of obesity remains unclear. We therefore examined the effect of sc leptin administration on BMD and markers of bone turnover in two women, one with congenital generalized lipodystrophy and the other with acquired generalized lipodystrophy. Both patients had regular menstrual cycles. At baseline, the BMD for both patients, measured at the lumbar spine and total hip, was within 1 SD of the peak bone mass. There was no significant change in BMD in both patients after 16-18 months of leptin therapy. Similarly, concentrations of serum osteocalcin and bone-specific alkaline phosphatase or urinary excretion of deoxypyridinoline and N-telopeptides remained unchanged after 6-8 months of leptin therapy, suggesting no effects of leptin on osteoblastic or osteoclastic activity. Our preliminary data suggest that sc leptin replacement in hypoleptinemic patients with generalized lipodystrophy has no effect on the mature adult skeleton.

Relationships among body mass, its components, and bone

Body weight impacts on both bone turnover and bone density, and is therefore an important risk factor for vertebral and hip fractures, ranking in importance alongside that of age. The effect of body weight is probably contributed to by both fat mass and lean mass, although in postmenopausal women fat mass has been more consistently demonstrated to be important. A number of mechanisms for the fat-bone relationship exist and include the effect of soft tissue mass on skeletal loading, the association of fat mass with the secretion of bone-active hormones from the pancreatic beta cell (including insulin, amylin, and preptin), and the secretion of bone-active hormones (e.g., estrogens and leptin) from the adipocyte. These factors alone probably do not fully explain the observed clinical associations, and further study of the actions on bone of novel hormones related to nutrition is an important area of further research. An understanding of this aspect of bone biology may open the way for new treatments of osteoporosis. More immediately, the role of weight maintenance in the prevention of osteoporosis is an important public health message that needs to be more widely appreciated.

Relationship of serum leptin concentration with bone mineral density in the United States population

Overweight is associated with both higher bone mineral density (BMD) and higher serum leptin concentrations. In humans, little is known about the relationship of leptin concentration and bone density. We studied this relationship in a large, national population-based sample. Participants included 5815 adults in the Third U.S. National Health and Nutrition Examination Survey (NHANES III; 1988-1994) who underwent DXA of the proximal femur and measurement of fasting serum leptin. Mean +/- SE BMD (gm/cm2) of the total hip was 1.01 +/- 0.005 in men, 0.94 +/- 0.004 in premenopausal women, and 0.78 +/- 0.007 in postmenopausal women. Bone density increased with increasing leptin concentration in men (p = 0.003), premenopausal women (p < 0.001), and postmenopausal women (p < 0.001). However, after adjusting for body mass index (BMI) and other bone density-related factors, an inverse association emerged in men (p < 0.001), being most evident among men < 60 years old. There was no association of leptin and BMD in premenopausal women (p = 0.66) or postmenopausal women (p = 0.69) in multivariate analysis. Controlling for leptin had no effect on the strong positive association of BMI and BMD in either men or women. Serum leptin concentration did not appear to affect directly BMD. If present, the association appeared to be limited to younger men who are at lower risk of osteoporosis.

Is leptin the link between fat and bone mass?

Recently, leptin has emerged as a potential candidate responsible for protective effects of fat on bone tissue. However, it remains difficult to draw a clear picture of leptin effects on bone metabolism because published data are sometimes conflicting or apparently contradictory. Beyond differences in models or experimental procedures, it is tempting to hypothesize that leptin exerts dual effects depending on bone tissue, skeletal maturity, and/or signaling pathway. Early in life, leptin could stimulate bone growth and bone size through direct angiogenic and osteogenic effects on stromal precursor cells. Later, it may decrease bone remodeling in the mature skeleton, when trabecular bone turnover is high, by stimulating osteoprotegerin (OPG) expression. Leptin negative effects on bone formation effected through central nervous system pathway could counterbalance these peripheral and positive effects, the latter being predominant when the blood-brain barrier permeability decreases or the serum leptin level rises above a certain threshold. Thus, the sex-dependent specificity of the relationship between leptin and bone mineral density (BMD) in human studies could be, at least in part, caused by serum leptin levels that are two- to threefold higher in women than in men, independent of adiposity. Although these hypotheses remain highly speculative and require further investigations, existing studies consistently support the role of leptin as a link between fat and bone.

Leptin prevents the fall in plasma osteocalcin during starvation in male mice

Plasma osteocalcin, a marker of osteoblastic activity, is reduced in starvation, malnutrition, and anorexia nervosa, resulting in low bone turnover osteoporosis. Contradictory findings about the role of leptin as a link between nutritional status and bone physiology have been reported. We demonstrate that leptin-deficient ob/ob and leptin-resistant db/db male mice have increased plasma osteocalcin, and that in male ob/ob mice osteocalcin is not decreased by starvation, unlike control mice. Intraperitoneal leptin administration increased plasma osteocalcin in male ob/ob mice, and prevented its fall during 24h fasting and 5 days of food restriction in normal male mice. This effect may be mediated via actions on the hypothalamic-pituitary-testicular or -growth hormone axes, or a direct action on osteoblasts. These studies support the hypothesis that the fall in leptin during starvation and weight loss is responsible for the associated reduction in osteoblast activity, and suggest a role for leptin in regulating bone turnover.