Hyperinsulinemia and bone mineral density in an elderly population: The Rotterdam Study

Severe deficiencies of IGF-I, IGF-II, IGFBP-3, ALS and paradoxically high-normal bone mass in a child with insulin-resistance syndrome (Rabson-Mendenhall type)

Rabson-Mendenhall syndrome is a rare genetic disorder characterized by severe insulin resistance and hyperinsulinemia due to defects in signaling through the insulin receptor. Herein, we describe a new case of Rabson-Mendenhall syndrome in which investigations of the growth hormone (GH) - insulin-like growth factor (IGF) axis - reveal severe deficiencies in total and free insulin-like growth factor-I (IGF-I), IGF-II, IGF-binding protein-3 (IGFBP-3), and the acid labile subunit (ALS). Based on these findings, we anticipated significant bone deficits, as have been described in other clinical scenarios in which the IGF axis is significantly perturbed. Long-bone studies revealed no gross malformations. Paradoxically, DXA scanning revealed a total body bone density Z-score of +2.0 (0.8 gm/cm(2)), suggesting an overall high-normal BMD for age and a high BMD corrected for bone or height age. The mechanisms by which BMD is protected from severe deficiencies in the IGF-axis are unknown, yet may involve enhanced IGF sensitivity, increased local production of IGFs, and/or supra-physiological concentrations of insulin substituting for the actions of IGFs in bone.

Biphasic fracture risk in diabetes: a population-based study

Diabetes is associated with increased fracture rates but the effect size, time course and modifying factors are poorly understood. This study was undertaken to assess the effect of diabetes on fracture rates and possible interactions with age, duration of diabetes and comorbidity. A retrospective, population-based matched cohort study (1984-2004) was performed using the Population Health Information System (POPULIS) for the Province of Manitoba, Canada. The study cohort consisted of 82,094 diabetic adults and 236,682 non-diabetic matched controls. Diabetes was subclassified as long term, short term, and newly diagnosed. Number of ambulatory diagnostic groups (ADGs) was an index of comorbidity. Poisson regression was used to study counts of combined hip, wrist and spine (osteoporotic) fractures (5691 with diabetes and 16,457 without diabetes) and hip fractures (1901 with diabetes and 5224 without diabetes). Independent effects of longer duration of diabetes (p-for-trend<0.0001) and number of ADGs (p-for-trend<0.0001) were observed on fracture rates. Newly diagnosed diabetes showed a reduction in osteoporotic fractures (rate ratio [RR] 0.91 [95% CI, 0.86-0.95]) and hip fractures (RR 0.83 [0.75-0.92]). Long-term diabetes showed an increase in osteoporotic fractures (RR 1.15 [CI, 1.09-1.22]) and hip fractures (RR 1.40 [1.28-1.53]). We conclude that long-term diabetes is associated with increased fracture risk, whereas newly diagnosed diabetes shows a reduction in fractures. It is hypothesized that the opposing effects of overweight/obesity and diabetes-related complications contribute to the observed biphasic fracture risk, though causality cannot be proven from this observational study.

Serum adiponectin and bone mineral density in women

CONTEXT

Bone mineral density (BMD) is positively associated with body weight. This association persists even at non-load bearing sites, suggesting that a nonmechanical factor such as an adipocyte-derived hormone may modulate BMD.

OBJECTIVE

The objective of the study was to evaluate the relationship between adiponectin, an adipocyte-derived hormone, and BMD.

DESIGN, SETTING, PARTICIPANTS

A total of 1735 nondiabetic women were recruited from a large, population-based cohort (mean age, 50.0 yr). We employed linear regression methods to estimate the relationship between adiponectin and BMD.

MAIN OUTCOME MEASURES

Percentage change in BMD (as measured at total hip, spine, femoral neck, and forearm) and markers of bone turnover associated with a doubling of fasting serum adiponectin levels were measured.

RESULTS

Employing age-adjusted analysis, each doubling of serum adiponectin was associated with a mean 2.7% decrease in BMD [total hip, -3.2% (95% confidence interval, -4.1, -2.3); femoral neck, -3.1% (-4.0, -2.1); forearm, -2.0 (-2.6, -1.4); spine, -2.6 (-3.5, -1.7)]. After adjustment for potential confounding factors, including BMI, serum leptin, central fat mass, hormone replacement therapy, smoking, and exercise, this relationship persisted, although decreased in magnitude. When stratified by menopausal status, the relationship between serum adiponectin and BMD strengthened in postmenopausal women but disappeared in premenopausal women. Serum adiponectin was positively associated with serum osteocalcin but not with urine deoxypyridinoline.

CONCLUSIONS

After adjustment of measures of body fat, increasing levels of adiponectin were associated with a decrease in BMD, even at non-load bearing sites. These data suggest that adiponectin, an adipocyte-derived hormone, may play a role in bone metabolism through nonmechanical mechanisms and that this effect may be mediated by menopausal status.

Insulin-like effects of visfatin on human osteoblasts

Visfatin (also known as pre-B cell colony-enhancing factor or PBEF) is a novel adipocytokine that is highly expressed in visceral fat and upregulated in obesity and type 2 diabetes mellitus. Visfatin binds to and activates the insulin receptor (IR), thereby exerting insulin-mimetic effects in various cell lines. IR has been detected in osteoblasts, which is consistent with the role of insulin as an important osteotropic hormone. This study investigated the actions of visfatin on human primary osteoblasts. The expression and tyrosine phosphorylation of IR, IR substrate-1 (IRS-1), and IRS-2 were determined by immunoprecipitation and immunoblotting. Cell proliferation was determined by measuring [(3)H]thymidine incorporation and cell number. Glucose uptake was determined by measuring 2-[(3)H]deoxyglucose incorporation. Real-time quantitative reverse-transcription polymerase chain reaction (PCR) was used for determining alkaline phosphatase (ALP), osteocalcin, and type I collagen mRNA expression. Enzyme-linked immunosorbent assay and radioimmunoassay were used for measuring ALP activity, osteocalcin secretion, and type I collagen production. We found that visfatin induced tyrosine phosphorylation of IR, IRS-1, and IRS-2. Moreover, the effects of visfatin - glucose uptake, proliferation, and type I collagen enhancement of cultured human osteoblast-like cells - bore a close resemblance to those of insulin and were inhibited by hydroxy-2-naphthalenylmethylphosphonic acid tris-acetoxymethyl ester, a specific inhibitor of IR tyrosine kinase activity. We also unexpectedly found that visfatin downregulated osteocalcin secretion from human osteoblast-like cells. These data indicate that the regulation of glucose uptake, proliferation, and type I collagen production by visfatin in human osteoblasts involves IR phosphorylation, the same signal-transduction pathway used by insulin.

High bone density is associated with prostate cancer in older Afro-Caribbean men: Tobago prostate survey

OBJECTIVE

To test the hypothesis that bone mineral density (BMD), a possible surrogate of lifetime exposure to hormone/growth factor/vitamin D/calcium exposure, is higher in prostate cancer cases than controls.

METHODS

Hip BMD was measured by dual X-ray absorptiometry in 222 Afro-Caribbean screening-detected prostate cancer cases and 1,503 screened non-cases, aged 45-79, in the population-based Tobago Prostate Survey. Because possible skeletal metastases may modulate BMD, men with prostate specific antigen >20 ng/ml or highly undifferentiated tumors (Gleason score > or = 8) were excluded. Mean BMD, adjusted for age and body mass index, was compared in cases and non-cases by analysis of variance. Risk across age group-specific BMD quartiles was compared using logistic regression.

RESULTS

Overall, adjusted mean hip BMD was higher in cases (1.157 g/cm2) than non-cases (1.134 g/cm2) (p = 0.02). In men aged 60-79, prostate cancer risk was two-fold higher (OR, 2.12; 95% CI: 1.21-3.71) in the highest BMD quartile compared to the lowest. There was no association in younger men (interaction, p = 0.055).

CONCLUSIONS

High bone density is associated with prostate cancer among older men, consistent with an etiological role for lifetime exposure to factors which modulate bone density. However, other etiologies may dominate prostate cancer risk among younger men.

Prospective study of diabetes and risk of hip fracture: the Nurses' Health Study

OBJECTIVE

The purpose of this study was to determine whether women with type 1 and type 2 diabetes are at higher risk of hip fractures.

RESEARCH DESIGN AND METHODS

A total of 109,983 women aged 34-59 years in 1980 were followed through 2002 for the occurrence of hip fracture. At baseline and through biennial follow-up, women were asked about their history and treatment of diabetes and other potential risk factors for hip fracture.

RESULTS

During 2.22 million person-years of follow-up, 1,398 women had a hip fracture. Compared with women without diabetes, the age-adjusted relative risk (RRs) of hip fracture was 7.1 (95% CI 4.4-11.4) for women with type 1 diabetes and 1.7 (1.4-2.0) for those with type 2 diabetes. After further adjustment for BMI, smoking, physical activity, menopausal status, daily intake of calcium, vitamin D, protein, and postmenopausal hormone use, the multivariate RR of incident hip fracture in individuals with type 1 diabetes compared with individuals without diabetes was 6.4 (3.9-10.3) and with type 2 diabetes was 2.2 (1.8-2.7). The RRs increased with longer duration of type 2 diabetes (3.1 [2.3-4.0] for >or=12 years compared with no diabetes, P for trend < 0.001) and ever use of insulin.

CONCLUSIONS

These data indicate that both type 1 and type 2 diabetes are associated with an increased risk of hip fracture. The results of this study highlight the need for fracture-prevention strategies in women with diabetes.

Bone mineral density and its determinants in diabetes: the Fremantle Diabetes Study

AIMS/HYPOTHESIS

We assessed the effects of type 1 and type 2 diabetes on bone density and metabolism.

MATERIALS AND METHODS

We analysed bone mineral density (BMD) measured at the hip, spine and forearm using dual energy X-ray absorptiometry in 34 patients with type 1 and 194 patients with type 2 diabetes. Patients were from the community-based Fremantle Diabetes Study, and findings for them were compared with those from normal age- and sex-matched control subjects from the local community. Biochemical and hormonal markers of bone metabolism were measured in a subset of 70 patients.

RESULTS

After adjusting for age and BMI, there was a lower BMD at total hip (p<0.001) and femoral neck (p=0.012) in type 1 men vs control subjects, but type 1 women and matched controls had similar BMD at each site. There was a higher BMD at total hip (p=0.006), femoral neck (p=0.026) and forearm (p<0.001) in type 2 women vs control subjects, but diabetes status was not associated with BMD in type 2 men after adjustment for age and BMI. Serum oestradiol, BMI, C-terminal telopeptide of collagen type 1 and male sex were consistently and independently associated with BMD at forearm, hip and femoral neck and explained 61, 55 and 50% of the total variance in BMD, respectively, at these sites. Spine BMD was independently associated with BMI and ln(oestradiol).

CONCLUSIONS/INTERPRETATION

Men with type 1 diabetes may be at increased risk of osteoporosis, while type 2 women appear to be protected even after adjusting for BMI. Low serum oestradiol concentrations may predispose to diabetes-associated osteoporosis regardless of sex.

Assessment of mandibular bone mineral density in patients with type 2 diabetes mellitus

OBJECTIVES

To assess mandibular bone mineral density in patients with type 2 diabetes mellitus using panoramic radiographs.

METHODS

Nineteen patients with type 2 diabetes mellitus and 17 control subjects participated in the study. Bone mineral density measurements were performed on the panoramic radiographs with the help of a five-step copper stepwedge phantom, attached to each film cassette, which was calibrated before hand by dual energy X-ray absorptiometry (DXA). The analysis was performed on digitized images by dedicated software (Scion Image). The accuracy of the measurement technique was also evaluated by cross-calibration with a DXA phantom.

RESULTS

Mean mandibular bone mineral density (g cm(-2)) was 1.53+/-0.27 in women and 1.52+/-0.29 in men with type 2 diabetes. In age and gender matched control subjects the values were 1.56+/-0.28 and 1.46+/-0.23 in women and in men, respectively. No statistically significant difference was observed between groups in mandibular bone mineral density.

CONCLUSIONS

The present study showed that bone mineral density of the mandible does not seem to be affected in patients with type 2 diabetes mellitus. We also observed that a panoramic radiograph could serve for accurate mandibular bone density determination, when calibrated well with the DXA method.

The interaction of ethnicity and chronic disease as risk factors for osteoporotic fractures: a comparison in Canadian Aboriginals and non-Aboriginals

INTRODUCTION

Efforts to develop global methods for absolute fracture risk prediction are currently limited by uncertainty over the validity of these models in non-White populations. Aboriginal Canadians have higher fractures rates than non-Aboriginals. This analysis examined the interaction of ethnicity with diabetes mellitus, disease comorbidity and substance abuse as possible explanatory variables.

METHODS

A retrospective, population-based matched cohort study of fracture rates was performed using Manitoba administrative health data (1984-2003). The study cohort consisted of 27,952 registered Aboriginal adults (aged 20 years or older) and 83,856 non-Aboriginal controls (matched three to one for year of birth and gender). Diabetes mellitus, number of ambulatory disease groups (ADGs), substance abuse and incident fractures were based upon validated definitions. Poisson regression analyses of fracture rates modelled the explanatory variables as main effects and two-way interactions with ethnicity.

RESULTS

Osteoporotic fracture rates were approximately twofold higher in the Aboriginal cohort (p<0.0001). Diabetes, greater number of ADGs and substance abuse were all more common in the Aboriginal cohort (all p<0.0001). These factors were associated with increased fracture rates (all p<0.0001) and significantly higher population attributable risk percent in the Aboriginal cohort (all p<0.0001). However, no significant interactions between the risk factors and ethnicity were observed (p>0.1 for all interaction effects).

CONCLUSION

Greater prevalence of diabetes, comorbidity and substance abuse contributes to higher rates of fracture. The relative risk of fracture for these factors is similar for both Aboriginal and non-Aboriginals despite large differences in absolute fracture risk and risk factor prevalence.

Bone mineral density and fracture risk in type-2 diabetes mellitus: the Rotterdam Study

The aim of this study was to determine the association between type-2 diabetes mellitus (DM), BMD and fractures in 6,655 men and women aged 55 years and over from the Rotterdam Study. We compared subjects with type-2 DM to subjects without DM. Additionally, subset analyses were performed, dividing subjects on the basis of the glucose tolerance test into already treated DM, newly diagnosed DM, impaired glucose tolerance (IGT) and normal glucose tolerance (NGT, reference). Femoral neck and lumbar spine BMD were measured using DEXA. Nonvertebral fracture ascertainment was performed using an automated record system involving GPs and local hospitals. Although subjects with DM had higher BMD, they had an increased nonvertebral fracture risk: hazard ratio (HR) 1.33 (1.00-1.77). In subset analysis, the increased fracture risk appeared restricted to treated DM subjects only: HR 1.69 (1.16-2.46). Subjects with IGT had a higher BMD, but contrary to treated DM, they had a lower fracture risk: HR 0.80 (0.63-1.00). In conclusion, subjects with type-2 DM and IGT both have a higher BMD. Whereas, subjects with IGT have a decreased fracture risk, subjects with DM (primarily those with already established and treated DM) had an increased fracture risk, probably due to long-term complications associated with DM.

Decreased bone mineral density at the distal radius, but not at the lumbar spine or the femoral neck, in Japanese type 2 diabetic patients

The purpose of this study is to assess the association between type 2 diabetes and bone mineral density. This study included 145 Japanese patients (64 men and 81 women) with type 2 diabetes and 95 non-diabetic control subjects (41 men and 54 women) of similar age. We measured bone mineral density (BMD) at the sites with different cortical/cancellous bone ratio (lumbar spine, femoral neck, and distal radius) using dual-energy X-ray absorptiometry. BMD and Z score at the distal radius were significantly lower in type 2 diabetic patients than those in control subjects, and in type 2 diabetic patients, the Z score at the distal radius was lower than that at their own lumbar spine and femoral neck. In type 2 diabetic patients, negative correlation between BMD and the mean HbA1c during the previous 2 years was found significantly at the distal radius in both genders and at the femoral neck in women. These results indicate the selective cortical bone loss in type 2 diabetes and suggest the importance of also determining BMD at the radius and keeping good metabolic control to prevent bone loss in type 2 diabetic patients.

Calcaneal bone mineral density in patients with Charcot neuropathic osteoarthropathy: differences between Type 1 and Type 2 diabetes

AIMS

To measure bone density and neuropathy in both feet in Type 1 and Type 2 patients with unilateral Charcot osteoarthropathy and controls.

METHODS

Calcaneal bone density, temperature and vibration thresholds were compared between 17 Type 1 diabetic patients with osteoarthropathy and 47 Type 1 controls and between 18 Type 2 diabetic patients and 48 Type 2 controls. As well as the Charcot foot, the non-Charcot foot was studied to assess osteopenia at onset of osteoarthropathy.

RESULTS

In Type 1 diabetes, bone density was reduced in the non-Charcot foot compared with controls [Z-score: -1.7 ({-1.9}-{-1.4}) vs. -0.2 ({-1.1}-{0.5}), P < 0.0001, median (interquartile range)]; but not in Type 2 diabetes [Z-score: 0.15 ({-0.45}-{0.85}) vs. 0.3 ({-0.5}-{0.9}), P = 0.675]. Bone density in the Charcot foot was lower compared with the non-Charcot foot in both Type 1 [Z-score: -2.0 ({-2.8}-{-1.4}) vs. -1.7 ({-1.9}-{-1.4}), P = 0.018] and Type 2 diabetes [Z-score: -0.2 ({-1.4}-{0.1}) vs. 0.3 ({-0.5}-{0.9}), P = 0.001]. In Type 1 diabetes, bone density of the non-Charcot foot was reduced compared with that in Type 2 (P < 0.0001). Body mass index was lower in Type 1 than in Type 2 Charcot patients (P = 0.007). Type 2 patients had high temperature (P = 0.001) and vibration thresholds (P < 0.0001) in the non-Charcot foot compared with Type 2 controls whereas Type 1 patients had a high temperature threshold (P = 0.01) but not vibration threshold compared with Type 1 controls (P = 0.077).

CONCLUSION

Bone density was reduced in the non-Charcot foot in Type 1 but not in Type 2 diabetes. Type 2 patients had high temperature and vibration thresholds in contrast to Type 1 patients who had a high temperature threshold only.

Diabetes and bone loss at the hip in older black and white adults

Type 2 diabetes may be associated with elevated fracture risk, but the impact on bone loss is unknown. Analysis of 4-year change in hip BMD data from a cohort of white and black well-functioning men and women 70-79 years of age found that white women with diabetes had more rapid bone loss at the femoral neck than those with normal glucose metabolism.

INTRODUCTION

Type 2 diabetes may be associated with elevated fracture risk in older adults. Although type 2 diabetes is not associated with lower BMD, older diabetic adults have a higher prevalence of other risk factors for fracture, including more frequent falls, functional limitations, and diabetic complications. With this burden of risk factors, loss of BMD could place older adults with diabetes at higher risk of sustaining a fracture.

MATERIALS AND METHODS

To determine if bone loss is increased with type 2 diabetes, we analyzed data from the Health, Aging, and Body Composition Study of white and black well-functioning men and women 70-79 years of age. Hip BMD was measured at baseline and 4 years later in 480 (23%) participants with diabetes, 439 with impaired glucose metabolism, and 1172 with normal glucose homeostasis (NG).

RESULTS

Those with diabetes had higher baseline hip BMD and weight, but among white women, had more weight loss over 4 years. White women with diabetes lost more femoral neck and total hip BMD than those with NG in age-adjusted models. After multivariable adjustment, diabetes was associated with greater loss of femoral neck BMD (-0.32%/year; 95% CI: -0.61, -0.02) but not total hip BMD. In men and black women, change in hip BMD was similar for participants with diabetes and NG.

CONCLUSIONS

Despite having higher baseline BMD, diabetic white women, but not men or black women, had more rapid bone loss at the femoral neck than those with NG. This increased bone loss may contribute to the higher fracture risk observed in older diabetic women.

Demographic risk factors for fracture in First Nations people

BACKGROUND

Recently, First Nations people were shown to be at high fracture risk compared with the general population. However, factors contributing to this risk have not been examined. This analysis focusses on geographic area of residence, income level, and diabetes mellitus as possible explanatory variables since they have been implicated in the fracture rates observed in other populations.

METHODS

A retrospective, population-based matched cohort study of fracture rates was performed using the Manitoba administrative health data (1987-1999). The First Nations cohort included all Registered First Nations adults (20 years or older) as indicated in either federal and/or provincial files (n = 32,692). Controls (up to three for each First Nations subject) were matched by year of birth, sex and geographic area of residence. After exclusion of unmatched subjects, analysis was based upon 31,557 First Nations subjects and 79,720 controls.

RESULTS

Overall and site-specific fracture rates were significantly higher in the First Nations cohort. Income quintile, geographic area of residence, and diabetes were fracture determinants but the excess fracture risk of First Nations ethnicity persisted even after adjustment for these factors.

CONCLUSION

First Nations people are at high risk for fracture but the causal factors contributing to this are unclear. Further research is needed to evaluate the importance of other potential explanatory variables.

The association of bone mineral density with insulin resistance in patients with polycystic ovary syndrome

OBJECTIVE

The aim of the study was to compare the bone mineral density (BMD) measurements between the patients with polycystic ovary syndrome (PCOS) and age and the body mass index (BMI) matched healthy controls, and to examine whether insulin resistance was associated with BMD.

STUDY DESIGN

Twenty-nine consecutive patients with PCOS and seventeen, age and BMI matched healthy control women were included in the study. Blood samples were obtained for follicle stimulating hormone, luteinizing hormone, estradiol, dehydroepiandrosterone-sulfate, 17 hydroxy-progesterone, free testosterone, sex hormone binding globulin, insulin, and glucose levels and BMD measurements were performed for total body, lumbar spine (L2-L4), and femoral neck for each participant. Insulin resistance was estimated by fasting insulin level, fasting glucose/insulin ratio and 75 g of glucose tolerance test for 2 h. Differences between the groups were analyzed by Student's t-test and Mann-Whitney U-test where appropriate. Correlation analysis between the parameters concerning insulin resistance and BMD measurements were performed in patients with PCOS using Pearson's correlation coefficient (r). Correlation analysis was also performed between serum hormone levels and BMD measurements in the PCOS group. Partial correlation coefficients were calculated for these parameters, using age and BMI as covariates.

RESULTS

Free testosterone and 17 hydroxy-progesterone levels were significantly high in patients with PCOS compared to the control women (P = 0.001 and 0.04, respectively). Fasting insulin was significantly higher and fasting glucose/insulin ratio was significantly lower in the PCOS group compared to the controls (P = 0.021 and 0.008, respectively). BMD measurements did not differ between the groups (P > 0.05). There were significant correlations between fasting insulin and total BMD (r = 0.424, P < 0.05) and fasting glucose/insulin ratio and L2-L4 BMD (r = -0.401, P < 0.05) after controlling for age and BMI.

CONCLUSION

BMD measurements are not different between the patients with polycystic ovary syndrome and healthy control women and hyperinsulinemia, and insulin resistance might play a role in the preserved BMD.

Fracture risk among First Nations people: a retrospective matched cohort study

BACKGROUND

Canadian First Nations people have unique cultural, socioeconomic and health-related factors that may affect fracture rates. We sought to determine the overall and site-specific fracture rates of First Nations people compared with non-First Nations people.

METHODS

We studied fracture rates among First Nations people aged 20 years and older (n = 32 692) using the Manitoba administrative health database (1987-1999). We used federal and provincial sources to identify ethnicity, and we randomly matched each First Nations person with 3 people of the same sex and year of birth who did not meet this definition of First Nations ethnicity (n = 98 076). We used a provincial database of hospital separations and physician billing claims to calculate standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) for each fracture type based on a 5-year age strata.

RESULTS

First Nations people had significantly higher rates of any fracture (age- and sex-adjusted SIR 2.23, 95% CI 2.18-2.29). Hip fractures (SIR 1.88, 95% CI 1.61-2.14), wrist fractures (SIR 3.01, 95% CI 2.63-3.42) and spine fractures (SIR 1.93, 95% CI 1.79-2.20) occurred predominantly in older people and women. In contrast, craniofacial fractures (SIR 5.07, 95% CI 4.74-5.42) were predominant in men and younger adults.

INTERPRETATION

First Nations people are a previously unidentified group at high risk for fracture.

Type 2 diabetes mellitus is associated with increased axial bone density in men and women from the Hertfordshire Cohort Study: evidence for an indirect effect of insulin resistance?

AIMS/HYPOTHESIS

Previous studies have suggested that the high bone density often observed in type 2 diabetic patients may be explained by insulin resistance. We explored this hypothesis in the Hertfordshire Cohort Study.

METHODS

A total of 465 men and 444 women aged 59 to 71 years and with no prior diagnosis of diabetes attended a clinic where a glucose tolerance test was performed and bone density measured at the femoral neck and lumbar spine. Biochemical markers of bone turnover (serum osteocalcin and urinary mean c-terminal cross-linking telopeptide of type II collagen) were measured in 163 men.

RESULTS

According to WHO criteria, 83 men and 134 women were diagnosed with impaired glucose tolerance and a further 33 men and 32 women were diagnosed as having type 2 diabetes. Bone density was higher in newly diagnosed diabetic subjects, with relationships stronger in women (p<0.001) than men (p<0.05) and attenuated by adjustment for body mass index. In both sexes, we observed positive correlations between the total femur and femoral neck bone mineral density with measures of insulin resistance (r=0.17-0.22), with stronger results observed in women. These relationships did not apply after adjustment for body mass index. Glucose status did not lead to differences in osteocalcin level or c-terminal cross-linking telopeptide of type II collagen levels.

CONCLUSIONS/INTERPRETATION

Our findings suggest that hyperinsulinaemia may affect bone mineral density through indirect effects, e.g. body weight.

Women, type 2 diabetes, and fracture risk

Older women with type 2 diabetes have an increased risk of nonspine fractures. The higher risk of falling associated with diabetes partially accounts for this increased risk. Current evidence suggests that there may also be impairments of bone strength in type 2 diabetes that are not well captured by bone mineral density testing. There is limited observational evidence that poor glycemic control and the associated complications of peripheral neuropathy and retinopathy may increase fractures, falls, and bone loss. However, this hypothesis has not been tested in a randomized trial. It remains to be elucidated whether treating diabetes and diabetic complications aggressively can alter skeletal health either directly or by preventing diabetic complications that contribute to falls and fractures. Health care professionals should be aware of the increased fracture risk among older women with diabetes and should ensure screening, treatment, and fall prevention strategies are appropriately implemented.

Diabetes is associated independently of body composition with BMD and bone volume in older white and black men and women: The Health, Aging, and Body Composition Study

The association between type 2 diabetes, BMD, and bone volume was examined to determine the effect of lean and fat mass and fasting insulin in the Health, Aging, and Body Composition Study, which included white and black well-functioning men and women 70-79 years of age (N = 2979). Diabetes predicted higher hip, whole body, and volumetric spine BMD, and lower spine bone volume, independent of body composition and fasting insulin.

INTRODUCTION

The purpose of this study was to determine if the association between type 2 diabetes and higher BMD observed in older white women is seen in elderly white men and blacks and to evaluate if higher BMD in diabetic individuals is accounted for by lean mass, fat mass, or fasting insulin differences.

MATERIALS AND METHODS

In the Health, Aging, and Body Composition Study, which included white and black well-functioning men and women 70-79 years of age (N = 2979), 19% of participants had diabetes at baseline. Of those with diabetes, 57% were men, and 62% were black. Multivariate linear regression models examined independent effects of diabetes, lean mass, fat mass, visceral fat, and fasting insulin on BMD and bone volume while adjusting for relevant covariates.

RESULTS AND CONCLUSIONS

Fasting insulin, visceral fat, and volumetric spine BMD, assessed by CT, and lean mass, fat mass, and total hip and whole body BMD, assessed by DXA, were higher (p < or = 0.05 for all) for those with diabetes. Hip BMD was higher in white men (0.99 +/- 0.14 versus 0.93 +/- 0.14 g/cm2, p < 0.001), black men (1.06 +/- 0.17 versus 1.00 +/- 0.15 g/cm2, p < 0.001), white women (0.83 +/- 0.13 versus 0.76 +/- 0.13 g/cm2, p < 0.001), and black women (0.90 +/- 0.15 versus 0.85 +/- 0.15 g/cm2, p < 0.001) with diabetes compared with those without diabetes, although the relationship was attenuated by body composition. In multiple regression models, diabetes was an independent predictor of higher hip, whole body, and volumetric spine BMD in all participants (p < or = 0.001), but lower spine volume (p = 0.01) and higher hip BMD for each race-gender group (p < or = 0.01). Type 2 diabetes was associated with a 4-5% higher total hip BMD in all race-gender groups of elderly adults, independent of body composition and fasting insulin levels.

Type 2 diabetes is associated with increased bone mineral density in Mexican-American women

BACKGROUND

Our purpose was to determine whether type 2 diabetes is associated with altered bone mineral density (BMD) and whether fasting serum insulin levels are correlated with BMD.

METHODS

In a population-based family study of Mexican-Americans, we obtained measurements of BMD, diabetes status (by 2-h oral glucose tolerance test), obesity, and serum insulin concentrations in 600 subjects from 34 families. Analyses were stratified by sex and conditioned on the pedigree structure to account for residual correlations among related individuals.

RESULTS

Women with diabetes had significantly higher BMD at hip than women without diabetes (p=0.03) even after adjustment for age, body mass index (BMI), and menopause status. BMD at spine was also higher in diabetic women than in nondiabetic women, although the association was no longer statistically significant after adjustment for BMI. Diabetes was not associated with BMD in men. In nondiabetic men and women, insulin levels were significantly correlated with BMD after adjustment for age and other lifestyle covariates, but correlations were diminished and were no longer statistically significant after further adjustment for body mass index.

CONCLUSIONS

These results suggest that Mexican-American women with type 2 diabetes have higher BMD compared to their nondiabetic counterparts, with the association independent of obesity at hip, although not at spine or forearm. Increased BMD was also correlated with serum insulin levels, although this association was not independent of obesity. Longitudinal studies may be required to better define the mechanisms underlying the observed association between BMD and diabetes.

Diabetes Mellitus: Does it Affect Bone?

Both diabetes and fractures affect a large proportion of older adults. Recent cohort studies indicate that diabetes itself is associated with increased risk of fracture of the hip, proximal humerus, and foot. Observational studies and animal models suggest that decreased bone strength in diabetes may contribute to fracture risk but this remains a controversial issue. Type 1 diabetes is associated with modest reductions in bone mineral density (BMD) but type 2 diabetes is often characterized by elevated BMD. This paradox of higher BMD but increased fracture risk in type 2 diabetes may be explained by a combination of more frequent falls and poorer bone quality. Diabetes can impact bone through multiple pathways, some with contradictory effects, including obesity, changes in insulin levels, higher concentrations of advanced glycation end products in collagen, hypercalciuria associated with glycosuria, reduced renal function, lower insulin-like growth factor-I, microangiopathy, and inflammation. A better understanding of how diabetes metabolism and treatments affect bone would improve fracture prevention efforts in older diabetic adults.

alpha -melanocyte-stimulating hormone is a novel regulator of bone

alpha-Melanocyte-stimulating hormone (alpha-MSH), a 13-amino acid peptide produced in the brain and pituitary gland, is a regulator of appetite and body weight, and its production is regulated by leptin, a factor that affects bone mass when administered centrally. alpha-MSH acts via melanocortin receptors. Humans deficient in melanocortin receptor 4 (MC4-R) have increased bone mass, and MC4-R has been identified in an osteoblast-like cell line. Thus alpha-MSH may act directly on the skeleton, a question addressed by the present studies. In primary cultures of osteoblasts and chondrocytes, alpha-MSH dose dependently (>or=10(-9) M) stimulated cell proliferation. In bone marrow cultures, alpha-MSH (>10(-9) M) stimulated osteoclastogenesis. Systemic administration of alpha-MSH to mice (20 injections of 4.5 microg/day) decreased the trabecular bone volume in the proximal tibiae from 19.5 +/- 1.8 to 15.2 +/- 1.4% (P = 0.03) and reduced trabecular number (P = 0.001). Radiographic indexes of trabecular bone, assessed by phase-contrast X-ray imaging, confirmed the bone loss. It is concluded that alpha-MSH acts directly on bone, increasing bone turnover, and, when administered systemically, it decreases bone volume. The latter result may also be contributed to by alpha-MSH effects elsewhere, such as the adipocyte, pancreatic beta-cell, or central nervous system.

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.

Mechanism of circadian variation in bone resorption

The diurnal variation in bone resorption markers is poorly understood and may contain essential information about regulation of bone resorption. To explore the acute regulation of bone resorption we studied bone turnover in 14 postmenopausal women during a randomized, crossover, 24 h study of oral glucose tolerance test (OGTT), normal diet, or fasting. Whereas fasting counteracted variation in bone resorption, as measured by serum C-telopeptide fragments of collagen type 1 degradation (s-CTx), OGTT and normal diet induced a 50% reduction (p < 0.001) over 2 h. For OGTT, s-CTx reverted to baseline levels after 6 h, and for normal diet s-CTx remained suppressed during the afternoon and returned to baseline overnight. Repeated OGTT at 8:00 A.M. and 8:00 P.M. in nine postmenopausal women demonstrated that identical reductions in s-CTx could be obtained at both timepoints with an intermediate return to baseline between tests. A 2 h randomized, crossover study of OGTT and fasting in 23 men and premenopausal women similarly revealed a 50% decrease in s-CTx. A randomized, crossover 2 h study of insulin tolerance test compared with fasting in six men and premenopausal women demonstrated a 20%-30% decrease in s-CTx (p < 0.01-0.05). Nine hour follow-up of ten healthy individuals during a crossover experiment of OGTT, protein, and fat intake revealed a comparable 50% reduction in s-CTx, but distinct profiles of serum glucose and serum insulin. Bone resorption was reduced by intake of food, glucose, fat, and protein and counteracted by fasting, and this seems to have been be independent of age and gender. Both exogenous and endogenous insulin stimulation tests induced a reduction in bone resorption, but this was only partial when compared with the reduction observed during food intake.

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

OBJECTIVE

Although total fat body mass (FM) is considered to be one of the major determinants of bone mass, the mechanism by which FM and bone mass are positively correlated remains unclear. Leptin, the product of the obese (ob) gene, is secreted from adipocytes and its plasma levels are known to be positively correlated with %fat (FM divided by total body weight). There is recent evidence suggesting that leptin directly stimulates osteoblastic differentiation. Thus it is possible that the anabolic action of this hormone on bone may participate in the positive correlation between FM and bone mass. In this study, we analysed the relationships between either plasma leptin levels or %fat vs. bone mineral density (BMD) values as well as the presence of vertebral compression fractures, and evaluated whether or not plasma leptin levels were associated with BMD or bone fragility in a manner independent of FM.

PATIENTS

One hundred and thirty-nine postmenopausal women (age 48-78 years, mean 62.5), who visited our outpatient clinic for the evaluation of osteoporosis.

DESIGN AND MEASUREMENTS

Plasma concentrations of leptin after an overnight fast were measured by radioimmunoassay. BMD values were measured by dual-energy X-ray absorptiometry (DXA) at the lumbar spine, femoral neck and whole body. Distal one-third of radius BMD was measured by single photon absorptiometry (SPA). Vertebral fractures were assessed by lateral thoracic and lumbar spine radiographs.

RESULTS

Although neither plasma leptin levels nor %fat correlated with age, there was a significant positive correlation between plasma leptin levels and %fat (r = 0.563, P < 0.001). Plasma leptin levels were significantly and positively correlated with BMD values at all skeleton sites measured, and multiple regression analysis revealed that this positive relationship was still observed with BMD values of the femoral neck and of the whole body, even after %fat and age were taken into account. Moreover, plasma leptin levels but not %fat were significantly lower in women with vertebral fractures than in those without fractures. When multiple logistic regression analysis was performed with either plasma leptin value or %fat employed as independent variables, plasma leptin values but not %fat were selected as an index affecting the presence of vertebral fractures.

CONCLUSION

Our study showed that plasma leptin levels but not %fat are associated with BMD and the presence of vertebral fractures in postmenopausal women, suggesting that circulating leptin might play a physiological role in maintaining bone mass as well as better bone quality.

Bone mass and breast cancer risk in older women: differences by stage at diagnosis

BACKGROUND

Older women with low bone mineral density (BMD) have a decreased incidence of breast cancer. It is not known whether this association is confined to early-stage, slow-growing tumors.

METHODS

We prospectively studied 8905 women who were 65 years of age or older during the period from 1986 through 1988 and had no history of breast cancer. At study entry, we used single-photon absorptiometry to measure each woman's BMD at three skeletal sites: the wrist, forearm, and heel. The women were followed for a mean of 6.5 years for the occurrence of breast cancer. All statistical tests were two-sided.

RESULTS

During 57 516 person-years of follow-up, 315 women developed primary invasive or in situ breast cancer. Multivariate analyses that adjusted for age, obesity, and other covariates revealed that the risk of breast cancer for women in the highest quartile of BMD for all three skeletal sites was 2.7 (95% confidence interval [CI] = 1.4 to 5.3) times greater than that for women in the lowest quartile at all three skeletal sites. The magnitude of increased risk associated with high BMD differed by the stage of disease at diagnosis and was greater for more advanced tumors (relative risk [RR] for TNM [i.e., tumor-lymph node-metastasis] stage II or higher tumors = 5.6; 95% CI = 1.2 to 27.4) than for early-stage disease (RR for in situ/TNM stage I tumors = 2.2; 95% CI = 1.0 to 4.8).

CONCLUSIONS

Elderly women with high BMD have an increased risk of breast cancer, especially advanced cancer, compared with women with low BMD. These findings suggest an association between osteoporosis and invasive breast cancer, two of the most prevalent conditions affecting an older woman's health.

Polycystic ovary syndrome, androgen excess, and the impact on bone

Polycystic ovary syndrome (PCOS) is a unique, natural model for the study of the influence of androgen excess on bone mass among women. Both thin and obese women develop PCOS, a presentation that allows for the evaluation of the effects of life-long obesity, alterations in body composition (central adiposity), and related metabolic abnormalities (hyperandrogenemia, hyperinsulinemia) on the skeleton. The relatively high prevalence of PCOS and its manifestation early in life render this disorder of particular importance in assessing the influence of androgens and androgen-estrogen balance on the attainment of maximal bone mass and subsequent development of osteoporosis later in life.

Insulin stimulates vitamin C recycling and ascorbate accumulation in osteoblastic cells

Insulin modulates the differentiation and synthetic activity of osteoblasts, but its mechanisms of action are not fully understood. Because ascorbate also influences osteoblast differentiation and is a cofactor for collagen synthesis, we examined the effects of insulin on the transport and metabolism of vitamin C in osteoblastic cells. UMR-106 rat osteoblast-like cells accumulated ascorbate intracellularly when incubated with dehydroascorbic acid (DHAA; oxidized vitamin C). Insulin increased the intracellular concentration of ascorbate derived from DHAA and also increased the initial rates of uptake of DHAA and 2-deoxyglucose, but not that of ascorbate. A half-maximal effect on DHAA uptake was observed with approximately 100 pM insulin, whereas insulin-like growth factor I (IGF-I) was less potent. Preincubation with insulin for 6-12 h was required for stimulation, similar to the period needed for increased expression of facilitative hexose transporters (GLUT). DHAA uptake was inhibited by the GLUT antagonist cytochalasin B as well as by the GLUT substrates D-glucose and 2-deoxyglucose, whereas L-glucose and fructose had no effect. We conclude that insulin and IGF-I stimulate osteoblastic uptake of DHAA through facilitative hexose transporters. The relative potency of insulin in stimulating DHAA uptake is consistent with mediation by insulin receptors. DHAA is reduced to ascorbate within osteoblasts, maintaining a high intracellular concentration of ascorbate available for collagen synthesis. Impaired uptake of DHAA may contribute to the osteopenia associated with type I diabetes. In addition, cytotoxic levels of DHAA may accumulate in the extracellular fluid due to decreased transport activity and competitive inhibition by elevated concentrations of glucose.