Risk factors for longitudinal bone loss in elderly men and women: the Framingham Osteoporosis Study

Association between caffeine intake and bone mass among young women: potential effect modification by depot medroxyprogesterone acetate use

This study assessed associations between habitual caffeine intake and bone mass among young women. Analyses of the entire study population revealed no significant associations, while analyses restricted to women using depot medroxyprogesterone acetate (DMPA) showed modest inverse associations between caffeine intake and bone mineral content (BMC).

INTRODUCTION

Some previous investigations among postmenopausal women suggest an inverse relationship between caffeine intake and bone mass, yet studies of this association among young women are few.

METHODS

The association between habitual caffeine intake and bone mass was evaluated prospectively in a population-based cohort of 625 females, aged 14 to 40 years, adjusting for relevant biological and lifestyle factors. Caffeinated beverage intake was self-reported, and bone mineral content (BMC) and bone mineral density (BMD) were measured at baseline and every 6 months throughout a 24-month follow-up period using dual-energy x-ray absorptiometry.

RESULTS

Cross-sectional analyses revealed no significant differences in mean BMC or BMD at baseline. Mean percentage and absolute changes in BMC and BMD were not associated with caffeine use. Repeated measures analyses similarly showed no significant association between caffeine intake at baseline and mean BMC or BMD measured during follow-up. However, among women using depot medroxyprogesterone acetate (DMPA), modest inverse associations between caffeine and BMC (but not BMD) were detected.

CONCLUSIONS

Our data suggest that heavy habitual consumption of caffeinated beverages does not adversely impact bone mass among young women in general. Greater caffeine intake may be associated with lower BMC among DMPA users.

The relationship between body composition and bone mineral content: threshold effects in a racially and ethnically diverse group of men

We examined BMC and body composition in 1,209 black, Hispanic, and white men. Weight, BMI, waist circumference, and fat mass were associated with BMC only up to certain thresholds, whereas lean mass exhibited more consistent associations. The protective influence of increased weight appears to be driven by lean mass.

INTRODUCTION

Reduced body size is associated with decreased bone mass and increased fracture risk, but associations in men and racially/ethnically diverse populations remain understudied. We examined bone mineral content (BMC) at the hip, spine, and forearm as a function of body weight, body mass index (BMI), waist circumference, fat mass (FM), and nonbone lean mass (LM).

METHODS

The design was cross-sectional; 363 non-Hispanic black, 397 Hispanic, and 449 non-Hispanic white residents of greater Boston participated (N = 1,209, ages 30-79 y). BMC, LM, and FM were measured by DXA. Multiple linear regression was used to describe associations.

RESULTS

Weight, BMI, waist circumference, and FM were associated with BMC only up to certain thresholds. LM, by contrast, displayed strong and consistent associations; in multivariate models, femoral neck BMC exhibited a 13% increase per 10 kg cross-sectional increase in LM. In models controlling for LM, positive associations between BMC and other body composition measures were eliminated. Results did not vary by race/ethnicity.

CONCLUSIONS

The protective effect of increased body size in maintaining bone mass is likely due to the influence of lean tissue. These results suggest that maintenance of lean mass is the most promising strategy in maintaining bone health with advancing age.

CLINICAL Review # : low body weight mediates the relationship between HIV infection and low bone mineral density: a meta-analysis

CONTEXT

HIV infection has been associated with low bone mineral density (BMD) in many cross-sectional studies, although longitudinal studies have not demonstrated accelerated bone loss. The cross-sectional studies may have been confounded by the failure to control for low body weight in HIV-infected patients.

OBJECTIVE

Our objective was to determine whether low body weight might explain the association of HIV infection with low BMD.

DATA SOURCES

MEDLINE and EMBASE were searched for English language studies published from 1966 to March 2007, and conference abstracts prior to 2007 were hand-searched.

STUDY SELECTION

All studies reporting BMD and weight or body mass index in adult patients with HIV and a healthy age- and sex-comparable control group were included. Nine of 40 identified studies and one of 68 identified abstracts were eligible.

DATA SYNTHESIS

We adjusted for the between-groups weight differences using regression coefficients from published cohorts of healthy men and women. On average, HIV-infected patients were 5.1 kg [95% confidence interval (CI), -6.8, -3.4; P < 0.001] lighter than controls. At all skeletal sites, unadjusted BMD was lower by 4.4-7.0% in the HIV-infected groups than the controls (P < 0.01). After adjustment for body weight, residual between-groups differences in BMD were small (2.2-4.7%) [lumbar spine, -0.02 (95% CI, -0.05, 0.01) g/cm2; P = 0.12; total hip, -0.02 (95% CI, -0.04, 0.00) g/cm2; P = 0.031; femoral neck, -0.04 (95% CI, -0.07, -0.01) g/cm2; P = 0.013; and total body, -0.03 (95% CI, -0.07, 0.01) g/cm2, P = 0.11].

CONCLUSION

HIV-infected patients are lighter than controls and low body weight may largely account for the high prevalence of low BMD reported in HIV-infected patients. However, in the setting of current treatment practice, HIV infection per se is not a risk factor for low BMD.

Hip structural geometry in old and old-old age: similarities and differences between men and women

INTRODUCTION

Changes in hip structure and geometry during aging contribute to decreased bone strength. Little is known, however, about these characteristics at advanced age, when fragility fractures are common. We examined hip structural geometry in men and women of old age (72-84 years) and old-old age (85-96 years) to determine (1) gender differences; (2) whether or not these differences are consistent with the increased occurrence of hip fracture in elderly women, compared to men; and (3) whether or not gender-specific changes are consistent with the increased occurrence of fragility fractures after age 80 in both men and women.

METHODS

We used Hip Structure Analysis (HSA) software to analyze bone densitometry scans from 916 community-dwelling men and women aged 72-96 years. We examined gender differences in hip geometry by age group (72-74, 75-79, 80-84, and >or=85 years) and between gender-specific age groups using multivariable linear regression.

RESULTS

At the femoral narrow neck, there was no gender difference at age 72-74 in bone mineral density (BMD), cortical thickness (CT), and buckling ratio (BR). In contrast, at age 85 or older women had 13% less BMD and CT than men and 8% higher BR. At the intertrochanteric region, women >or=85 years had 25-31% less BMD, cross-sectional bone area (CSA), and CT than men of comparable age, and 38% higher BR. These gender differences were approximately 10-20% greater than those between men and women in their 70s. In gender-specific comparisons, women showed increasing change in structural geometry with increasing age. At both narrow neck and trochanteric regions, women >or=85 years had nearly 35% higher BR, 15% less BMD and CT, and 10% less CSA than women aged 72-74 years. At the narrow neck, they also had 6% greater outer diameter than the youngest women and 8% lower section modulus (Z), an index of bending strength. In contrast, men showed significant age differences only at the narrow neck region, and only at 85 years or older, including 22% higher BR, 10% less BMD and CT, and 5% greater outer diameter, compared to men in their early 70s. Unlike women, men showed no age-associated decline in section modulus.

CONCLUSIONS

Gender differences in hip geometry consistent with increased fragility and fracture risk in elderly women, compared to men, continue into old-old age. Both men and women 85 or older show the most unfavorable features, suggesting a structural basis for the increased occurrence of hip fracture in both sexes at advanced age.

Effects of weight control during the menopausal transition on bone mineral density

BACKGROUND

Studies of weight loss and changes in bone mineral density (BMD) have primarily been short-term trials in obese subjects.

OBJECTIVE

We examined the effects of a 5-yr intervention designed to prevent menopausal weight gain or promote modest weight loss on BMD in premenopausal women participating in the Women's Healthy Lifestyle Project.

DESIGN

We enrolled 373 premenopausal women (age 44-50 yr) and randomly assigned them to either lifestyle intervention (175 women, low-fat dietary modification, weight loss, and physical activity intervention) or control group (198 women). BMD and body weight were measured at baseline, annual follow-up visits (18, 30, 42, and 54 months), and two postintervention follow-ups (66 and 78 months). BMD was measured by dual x-ray absorptiometry.

RESULTS

Over the 54 months of intervention, women in the intervention group lost 0.4 kg, whereas control women gained 2.6 kg (P = 0.011). The intervention group experienced significantly greater hip bone loss (-0.20%/yr) than the control group (-0.03%/yr). During the postintervention, differences in rates of bone loss disappeared. When considering both menopausal status and use of hormone therapy (HT), the annualized BMD changes were lower in women reporting HT use; nevertheless, among women on HT, those who lost more than 3% body weight experienced greater total hip BMD loss (-0.25%/yr) compared with those who gained weight (-0.02%/yr) (P = 0.025).

CONCLUSIONS

Women randomized to a lifestyle intervention aimed at preventing menopausal weight gain or promoting modest weight loss experienced greater rates of hip bone loss than control women.

Tea drinking is associated with benefits on bone density in older women

BACKGROUND

Impaired hip structure assessed by dual-energy X-ray absorptiometry (DXA) areal bone mineral density (aBMD) is an independent predictor for osteoporotic hip fracture. Some studies suggest that tea intake may protect against bone loss.

OBJECTIVE

Using both cross-sectional and longitudinal study designs, we examined the relation of tea consumption with hip structure.

DESIGN

Randomly selected women (n = 1500) aged 70-85 y participated in a 5-y prospective trial to evaluate whether oral calcium supplements prevent osteoporotic fractures. aBMD at the hip was measured at years 1 and 5 with DXA. A cross-sectional analysis of 1027 of these women at 5 y assessed the relation of usual tea intake, measured by using a questionnaire, with aBMD. A prospective analysis of 164 women assessed the relation of tea intake at baseline, measured by using a 24-h dietary recall, with change in aBMD from years 1 to 5.

RESULTS

In the cross-sectional analysis, total hip aBMD was 2.8% greater in tea drinkers (x: 806; 95% CI: 797, 815 mg/cm(2)) than in non-tea drinkers (784; 764, 803 mg/cm(2)) (P < 0.05). In the prospective analysis over 4 y, tea drinkers lost an average of 1.6% of their total hip aBMD (-32; -45, -19 mg/cm(2)), but non-tea drinkers lost 4.0% (-13; -20, -5 mg/cm(2)) (P < 0.05). Adjustment for covariates did not influence the interpretation of results.

CONCLUSION

Tea drinking is associated with preservation of hip structure in elderly women. This finding provides further evidence of the beneficial effects of tea consumption on the skeleton.

Sample size requirements for bone density precision assessments and effect on patient categorization: a Monte Carlo simulation study

A sample size of 30 degrees of freedom (df) for bone mineral density (BMD) precision studies may be insufficient for reliably categorizing change. Monte Carlo simulation was used to evaluate the effect of precision study sample size on identifying change in clinical patients. Least significant change (LSC) from 198 spine and 193 total hip scan-pairs was used to categorize change for 1420 patients undergoing BMD monitoring. Relative to this reference change fraction (RCF), LSC limits were identified that gave specified deviations from the RCF (-25% to +25%). Confidence limits (95% and 80%) for these LSC values (5 to 500 df) were estimated using 'bootstrap' samplings. A sample size providing 140 df is needed to avoid overdetecting spine change by 5% and 150 df to avoid underdetecting spine change by 5% with 95% confidence limits. A sample size of 30 df resulted in up to a 12.5% overdetection and 10.0% underdetection of spine or hip change based upon 95% confidence limits. In conclusion, assessing the effect of precision study sample size on classifying change in monitored patients is an important element of the precision assessment that is neglected in current recommendations. Sample sizes larger than 30 df are required if low levels of categorization error are to be achieved.

Genome-wide association with bone mass and geometry in the Framingham Heart Study

BACKGROUND

Osteoporosis is characterized by low bone mass and compromised bone structure, heritable traits that contribute to fracture risk. There have been no genome-wide association and linkage studies for these traits using high-density genotyping platforms.

METHODS

We used the Affymetrix 100K SNP GeneChip marker set in the Framingham Heart Study (FHS) to examine genetic associations with ten primary quantitative traits: bone mineral density (BMD), calcaneal ultrasound, and geometric indices of the hip. To test associations with multivariable-adjusted residual trait values, we used additive generalized estimating equation (GEE) and family-based association tests (FBAT) models within each sex as well as sexes combined. We evaluated 70,987 autosomal SNPs with genotypic call rates > or =80%, HWE p > or = 0.001, and MAF > or =10% in up to 1141 phenotyped individuals (495 men and 646 women, mean age 62.5 yrs). Variance component linkage analysis was performed using 11,200 markers.

RESULTS

Heritability estimates for all bone phenotypes were 30-66%. LOD scores > or =3.0 were found on chromosomes 15 (1.5 LOD confidence interval: 51,336,679-58,934,236 bp) and 22 (35,890,398-48,603,847 bp) for femoral shaft section modulus. The ten primary phenotypes had 12 associations with 100K SNPs in GEE models at p < 0.000001 and 2 associations in FBAT models at p < 0.000001. The 25 most significant p-values for GEE and FBAT were all less than 3.5 x 10(-6) and 2.5 x 10(-5), respectively. Of the 40 top SNPs with the greatest numbers of significantly associated BMD traits (including femoral neck, trochanter, and lumbar spine), one half to two-thirds were in or near genes that have not previously been studied for osteoporosis. Notably, pleiotropic associations between BMD and bone geometric traits were uncommon. Evidence for association (FBAT or GEE p < 0.05) was observed for several SNPs in candidate genes for osteoporosis, such as rs1801133 in MTHFR; rs1884052 and rs3778099 in ESR1; rs4988300 in LRP5; rs2189480 in VDR; rs2075555 in COLIA1; rs10519297 and rs2008691 in CYP19, as well as SNPs in PPARG (rs10510418 and rs2938392) and ANKH (rs2454873 and rs379016). All GEE, FBAT and linkage results are provided as an open-access results resource at http://www.ncbi.nlm.nih.gov/projects/gap/cgi-bin/study.cgi?id=phs000007 webcite.

CONCLUSION

The FHS 100K SNP project offers an unbiased genome-wide strategy to identify new candidate loci and to replicate previously suggested candidate genes for osteoporosis.

The effects of smoking on bone health

Osteoporotic fractures are a major public health problem in most developed countries and an increasing concern in much of the developing world. This healthcare burden will increase significantly worldwide over the next 20 years due to aging of the population. Smoking is a key lifestyle risk factor for bone loss and fractures that appears to be independent of other risk factors for fracture such as age, weight, sex and menopausal status. This review discusses the effects of smoking on bone health in pre-menopausal and post-menopausal women and men. Data from twin studies and the three main published meta-analyses are presented. Possible mechanisms by which smoking affects bone mass are reviewed. Despite smoking being a major lifestyle risk factor for osteoporosis, the mechanisms underlying smoking-associated bone loss and fracture risk remain poorly understood. The effect appears dose-dependent, and may be, at least partially, reversible. However, more work is required to confirm and characterize the reversibility of smoking-associated bone defects. Finally, strategies for quitting smoking are discussed. Encouragement of lifestyle alterations, including smoking cessation, should be a major component of any bone therapeutic programme.

Bone mineral density remains stable in HAART-treated HIV-infected men over 2 years

OBJECTIVE

Recently we reported that human immunodeficiency virus (HIV)-infected Caucasian men treated with highly active antiretroviral therapy (HAART) have normal weight-adjusted bone mineral density (BMD), in contrast to most other cross-sectional analyses, which have reported low BMD in HIV-infected patients. We have now addressed the question of whether there is accelerated BMD loss over time in HIV-infected men.

DESIGN

A 2-year, prospective, longitudinal study.

SUBJECTS

Twenty-three HAART-treated, HIV-infected men and 26 healthy controls.

MEASUREMENTS

All participants had measurements of BMD and bone-related laboratory parameters at baseline, and a repeat measurement of BMD at 2 years.

RESULTS

In the HIV-infected men the mean age was 47 years, the mean duration of infection was 8.2 years, and the mean duration of HAART was 54 months. Over 2 years of follow-up, BMD increased from baseline in the HIV-infected men by 2.6% at the lumbar spine (P = 0.05 vs. baseline), and remained stable at the total hip (mean change 0.1%, P > 0.99) and total body (mean change 0.6%, P = 0.39). Mean changes in BMD in the control group were 1.4% at the lumbar spine, -0.1% at the total hip, and -0.8% at the total body. The HIV-infected men lost less total body BMD than the control group (P = 0.01). In the HIV-infected men, body weight remained stable over 2 years while fat mass decreased and lean mass tended to increase, whereas in the controls, body weight and fat mass increased while lean mass remained stable.

CONCLUSIONS

Accelerated bone loss does not occur in HIV-infected men treated with HAART. Monitoring of BMD in HIV-infected men may not be necessary.

Dihydrophylloquinone intake is associated with low bone mineral density in men and women

BACKGROUND

Poor diet may affect bone status by displacing nutrients involved in bone health. Dihydrophylloquinone, a form of vitamin K present in foods made with partially hydrogenated fat, is a potential marker of a low-quality dietary pattern.

OBJECTIVE

Our objective was to examine the cross-sectional associations between dihydrophylloquinone intake and bone mineral density (BMD) of the hip and spine in men and women.

DESIGN

Dihydrophylloquinone intake was estimated with a food-frequency questionnaire, and BMD (in g/cm(2)) was measured by dual-energy X-ray absorptiometry in 2544 men and women (mean age: 58.5 y) who had participated in the Framingham Offspring Study. General linear models were used to examine the associations between dihydrophylloquinone intake (in tertiles: <15.5, 15.5-29.5, and >29.5 microg/d) and hip and spine BMD after adjustment for age, body mass index, energy intake, calcium intake, vitamin D intake, smoking status, physical activity score, and, for women, menopause status and estrogen use.

RESULTS

Higher dihydrophylloquinone intakes were associated with lower mean BMD at the femoral neck [lowest-to-highest tertiles (95% CI): 0.934 (0.925, 0.942), 0.927 (0.919, 0.935), and 0.917 (0.908, 0.926), P for trend = 0.02], the trochanter [lowest-to-highest tertiles (95% CI): 0.811 (0.802, 0.820), 0.805 (0.797, 0.813), and 0.795 (0.786, 0.804), P for trend = 0.02], and the spine [lowest-to-highest tertiles (95% CI): 1.250 (1.236, 1.264), 1.243 (1.242, 1.229), and 1.227 (1.213, 1.242), P for trend = 0.03] in men and women after adjustment for the covariates. Further adjustment for markers of healthy and low-quality dietary patterns did not affect the observed associations.

CONCLUSIONS

Higher dihydrophylloquinone intakes are associated with lower BMD in men and women. This association remains significant after adjustment for other markers of diet quality.

Predictors of low bone mineral density in the elderly: the role of dietary intake, nutritional status and sarcopenia

OBJECTIVES

The aims of this study were to investigate the relationship between sarcopenia, dietary intake, nutritional indices and hip bone mineral density (BMD) in the elderly, and to estimate the risk of low BMD due to specific independent predictor thresholds.

SUBJECTS AND METHODS

Body mass index (BMI), serum albumin, energy and protein intake were studied in 352 elderly outpatients (216 women aged 73.5+/-5.3 years and 136 men aged 73.9+/-5.6 years). BMD at different hip sites and appendicular skeletal muscle mass (ASMM) were assessed by dual-energy X-ray absorptiometry.

RESULTS

The prevalence of osteoporosis was 13% in men and 45% in women, while the prevalence of sarcopenia (50%) and hypoalbuminemia (5%) were similar in both genders. BMI, albumin and ASMM were significantly associated with BMD in both genders: so was protein intake, but only in men. By multiple regression analysis, the variables that retained their independent explanatory role on total hip BMD, were BMI and protein intake in men, and BMI and albumin in women. By logistic regression analysis, men risked having a low BMD with a BMI <22 (OR=12) and a protein intake <65.7 g/day (OR=3.7). Women carried some risk already in the BMI 25-30 class (OR=5), and a much greater risk in the BMI <22 class (OR=26). Albumin <40 g/l also emerged as an independent risk factor (OR=2.6).

CONCLUSIONS

BMI in both genders, albumin in women and protein intake in men have an independent effect on BMD. BMI values <22 are normal for younger adults but carry a higher risk of osteoporosis in the elderly, particularly in women. Age-related sarcopenia does not seem to be involved in bone mass loss.

Biochemical markers in preclinical models of osteoporosis

Although several treatments for osteoporosis exist, further understanding of the mode of action of current treatments, as well as development of novel treatments, are of interest. Thus, preclinical models of osteoporosis are very useful, as they provide the possibility for gaining knowledge about the cellular mechanisms underlying the disease and for studying pharmaceutical prevention or intervention of the disease in simple and strictly controlled systems. In this review, we present a comprehensive collection of studies using biochemical markers of bone turnover for investigation of preclinical models of osteoporosis. These range from pure and simple in vitro systems, such as osteoclast cultures, to ex vivo models, such as cultures of embryonic murine tibiae and, finally, to in vivo models, such as ovariectomy and orchidectomy of rats. We discuss the relevance of the markers in the individual models, and compare their responses to those observed using 'golden standard' methods.

Bone loss in elderly men: increased endosteal bone loss and stable periosteal apposition. The prospective MINOS study

INTRODUCTION

Longitudinal studies on the age-related bone loss in men concerns the decrease in areal bone mineral density (aBMD), which can be qualified as "apparent bone loss" because it does not reflect the change in bone mineral content (BMC). Loss of BMC can be referred to as "net bone loss" because it does not take into account the morphological basis of the bone loss (decreased periosteal apposition; endosteal bone loss, i.e. bone loss on the trabecular, endocortical and intracortical surfaces). The aim of this study was to assess age-related apparent net and endosteal bone loss as well as their morphological basis and age-related changes during a prospective follow-up in a large cohort of elderly men.

METHODS

This analysis was performed in 725 men aged 51-85 at baseline who were followed up for 90 months.

RESULTS

Bone densitometry was carried out at the lumbar spine, hip and whole body by using the HOLOGIC QDR1500 device and at the distal forearm by using the Osteometer DTX100 device. Sixty-five men who abandoned the study after the first examination were older and had lower aBMC at most sites of measurement. Apparent bone loss was significant at the hip, distal forearm and whole body. Net bone loss was also significant at these sites, except for the femoral neck. Periosteal expansion was significant at all sites of measurement. Apparent and net bone loss accelerated with age, whereas the rate of periosteal expansion remained stable. At the distal radius and ulna, endosteal bone loss accelerated with age, whereas the rate of periosteal apposition remained stable.

CONCLUSION

In a large cohort of elderly men, age-related apparent bone loss (aBMD) at the hip, distal forearm and whole body was determined by the net bone loss (BMC), except for the femoral neck. Apparent and net bone loss accelerated with age, whereas the periosteal expansion rate (bone widening) remained constant. At the distal forearm, age-related acceleration of the apparent bone loss was determined by the higher endosteal bone loss, whereas the periosteal apposition rate (estimated mass of deposited bone) remained constant.

Two-year randomized controlled trial of vitamin K1 (phylloquinone) and vitamin D3 plus calcium on the bone health of older women

Dietary supplementation with vitamin K(1), with vitamin D(3) and calcium or their combination, was examined in healthy older women during a 2-year, double-blind, placebo-controlled trial. Combined vitamin K with vitamin D plus calcium was associated with a modest but significant increase in BMC at the ultradistal radius but not at other sites in the hip or radius.

INTRODUCTION

The putative beneficial role of high dietary vitamin K(1) (phylloquinone) on BMD and the possibility of interactive benefits with vitamin D were studied in a 2-year double-blind, placebo-controlled trial in healthy Scottish women > or =60 years of age.

MATERIALS AND METHODS

Healthy, nonosteoporotic women (n = 244) were randomized to receive either (1) placebo, (2) 200 microg/day vitamin K(1), (3) 10 microg (400 IU) vitamin D(3) plus 1000 mg calcium/day, or (4) combined vitamins K(1) and D(3) plus calcium. Baseline and 6-month measurements included DXA bone mineral scans of the hip and wrist, markers of bone turnover, and vitamin status. Supplementation effects were tested using multivariate general linear modeling, with full adjustment for baseline and potential confounding variables.

RESULTS

Significant bone mineral loss was seen only at the mid-distal radius but with no significant difference between groups. However, women who took combined vitamin K and vitamin D plus calcium showed a significant and sustained increase in both BMD and BMC at the site of the ultradistal radius. Serum status indicators responded significantly to respective supplementation with vitamins K and D. Over 2 years, serum vitamin K(1) increased by 157% (p < 0.001), the percentage of undercarboxylated osteocalcin (%GluOC) decreased by 51% (p < 0.001), serum 25-hydroxyvitamin D [25(OH)D] increased by 17% (p < 0.001), and PTH decreased by 11% (p = 0.049).

CONCLUSIONS

These results provide evidence of a modest synergy in healthy older women from nutritionally relevant intakes of vitamin K(1) together with supplements of calcium plus moderate vitamin D(3) to enhance BMC at the ultradistal radius, a site consisting of principally trabecular bone. The substantial increase in gamma-carboxylation of osteocalcin by vitamin K may have long-term benefits and is potentially achievable by increased dietary intakes of vitamin K rather than by supplementation.

African-American women: health beliefs, lifestyle, and osteoporosis

Cultural beliefs of African-American women, manifested in lifestyle behaviors, may influence osteoporosis development. Genetics may have a positive influence on bone density, but the risks increase from other diseases that may contribute to the development of secondary osteoporosis. Health beliefs, lifestyle behaviors, and secondary osteoporosis causes are explored, focusing on relationships with osteoporosis. African-American women must be informed of the risks involved with some of the traditional health beliefs and practices. Healthcare providers have a challenge and responsibility to explore cultural beliefs with African-American women and to develop an acceptable approach to osteoporosis prevention.

Caffeine decreases vitamin D receptor protein expression and 1,25(OH)2D3 stimulated alkaline phosphatase activity in human osteoblast cells

Of the various risk factors contributing to osteoporosis, dietary/lifestyle factors are important. In a clinical study we reported that women with caffeine intakes >300 mg/day had higher bone loss and women with vitamin D receptor (VDR) variant, tt were at a greater risk for this deleterious effect of caffeine. However, the mechanism of how caffeine effects bone metabolism is not clear. 1,25-Dihydroxy vitamin D(3) (1,25(OH)(2)D(3)) plays a critical role in regulating bone metabolism. The receptor for 1,25(OH)(2)D(3), VDR has been demonstrated in osteoblast cells and it belongs to the superfamily of nuclear hormone receptors. To understand the molecular mechanism of the role of caffeine in relation to bone, we tested the effect of caffeine on VDR expression and 1,25(OH)(2)D(3) mediated actions in bone. We therefore examined the effect of different doses of caffeine (0.2, 0.5, 1.0 and 10mM) on 1,25(OH)(2)D(3) induced VDR protein expression in human osteoblast cells. We also tested the effect of different doses of caffeine on 1,25(OH)(2)D(3) induced alkaline phosphatase (ALP) activity, a widely used marker of osteoblastic activity. Caffeine dose dependently decreased the 1,25(OH)(2)D(3) induced VDR expression and at concentrations of 1 and 10mM, VDR expression was decreased by about 50-70%, respectively. In addition, the 1,25(OH)(2)D(3) induced alkaline phosphatase activity was also reduced at similar doses thus affecting the osteoblastic function. The basal ALP activity was not affected with increasing doses of caffeine. Overall, our results suggest that caffeine affects 1,25(OH)(2)D(3) stimulated VDR protein expression and 1,25(OH)(2)D(3) mediated actions in human osteoblast cells.

Depressive symptoms as a risk factor for osteoporosis and fractures in older Mexican American women

INTRODUCTION AND HYPOTHESIS

Despite higher rates of depression, lower hormone replacement therapy (HRT) use, and inadequate knowledge of factors associated with osteoporosis, Mexican Americans have been understudied with regards to the association between depression, osteoporosis, and fractures. We hypothesized that depression increases the risk for osteoporosis and fractures among older Mexican American women.

METHODS

Seven years of prospective data (1993-2001) from the Hispanic Established Populations for Epidemiologic Studies of the Elderly were analyzed for 1,350 women in the Southwest United States who had complete data for at least the first follow-up interview.

RESULTS

Respondents (mean age:75) were generally poorly educated, had low income, and reported poor or fair health. High levels of depressive symptoms were reported by 31%, while new diagnosis of osteoporosis and new fractures were reported by 18 and 13%, respectively. Logistic regression analyses showed that predictors of newly diagnosed osteoporosis included age, high school (HS) education, ever having been an alcoholic, early menopause, hormone replacement therapy, and high levels of depressive symptoms. Factors predictive of new fractures included age, HS education, diabetes, early menopause, and high levels of depressive symptoms.

CONCLUSIONS

Depressive symptoms were associated with increased risk of osteoporosis and new fractures, even after controlling for other predictive factors.

Genetic variation at the low-density lipoprotein receptor-related protein 5 (LRP5) locus modulates Wnt signaling and the relationship of physical activity with bone mineral density in men

Polymorphisms in the LRP5 gene have been associated with bone mineral density (BMD) in men and/or women. However, the functional basis for this association remains obscure. We hypothesized that LRP5 alleles could modulate Wnt signaling and the relationship between physical activity and BMD. This genetic association study was performed in the population-based Framingham Study Offspring Cohort, and included a subset of 1797 unrelated individuals who provided blood samples for DNA and who had BMD measurements of the hip and spine. Ten single-nucleotide polymorphisms (SNPs) spanning the LRP5 gene were genotyped and used for association and interaction analyses with BMD by regression methods. LRP5 haplotypes were transiently co-expressed with Wnt3a, MesD and Dkk1 in HEK293 cells and their activity evaluated by the TCF-Lef reporter assay. Six out of ten SNPs in LRP5 were associated with one or more of the femur or spine BMDs in men or women after adjustment for covariates, and these associations differed between genders. In men< or =age 60 years, 3 SNPs were significantly associated with BMD: rs2306862 on Exon 10 with femoral neck BMD (p=0.01) and Ward's BMD (p=0.01); rs4988321/p. V667M with Ward's BMD (p=0.02); and intronic rs901825 with trochanter BMD (p=0.03). In women, 3 SNPs in intron 2 were significantly associated with BMD: rs4988330 for trochanter (p=0.01) and spine BMD (p=0.003); rs312778 with femoral neck BMD (p=0.05); and rs4988331 with spine BMD (p=0.04). For each additional rare allele, BMD changed by 3-5% in males and 2-4% in females. Moreover, there was a significant interaction between physical activity and rs2306862 in exon 10 (p for interaction=0.02) and rs3736228/p. A1330V in exon 18 (p for interaction=0.05) on spine BMD in men. In both cases, the TT genotype was associated with lower BMD in men with higher physical activity scores, conversely with higher BMD in men with lower physical activity scores. In vitro, TCF-Lef activity in presence of Wnt3a was significantly reduced in cells expressing LRP5 haplotypes carrying the T allele of exon 10 and 18 compared to the wild-type allele, whereas co-expression of Dkk1 completely inhibited Wnt3a response through all LRP5 haplotypes. In summary, genetic variation in exons 10 and 18 of the LRP5 gene modulates Wnt signaling and the relationship between physical activity and BMD in men. These observations suggest that Wnt-LRP5 may play a role in the adaptation of bone to mechanical load in humans, and may explain some gender-related differences in bone mass.

The association between body mass index and osteoporosis in patients referred for a bone mineral density examination

PURPOSE

Osteoporosis affects 4-6 million (13%-18%) postmenopausal white women in the United States. Most studies to date on risk factors for osteoporosis have considered body mass index (BMI) only as a possible confounder. In this study, we assess the direct relationship between BMI and osteoporosis.

METHODS

We conducted a cross-sectional study among women aged 50-84 years referred by their physicians for a bone mineral density (BMD) examination at Baystate Medical Center between October 1998 and September 2000. BMI was determined prior to the BMD examination in the clinic. Information on other risk factors was obtained through a mailed questionnaire. Ordinal logistic regression was used to model the association between BMI and osteoporosis, controlling for confounding factors.

RESULTS

BMI was inversely associated with BMD status. After adjustment for age, prior hormone replacement therapy (HRT) use, and other factors, odds ratios (OR) for low, high, and obese compared with moderate BMI women were 1.8 (95% CI 1.2-2.7), 0.46 (95% CI 0.29- 0.71), and 0.22 (95% CI 0.14-0.36), respectively, with a significant linear trend (p < 0.0001) across BMI categories. Evaluating BMI as a continuous variable, the odds of bone loss decreased 12% for each unit increase in BMI (OR = 0.88, 95% CI 0.85-0.91).

CONCLUSIONS

Women with low BMI are at increased risk of osteoporosis. The change in risk associated with a 1 unit change in BMI ( approximately 5-8 lb) is of greater magnitude than most other modifiable risk factors. To help reduce the risk of osteoporosis, patients should be advised to maintain a normal weight.

Bone Mineral Density and its Related Factors in Elderly Male Chinese Patients with Type 2 Diabetes

BACKGROUND

There have been few investigations conducted on the epidemiology and risk factors of osteoporosis in patients with diabetes in China. The aim of this study was to disclose the percentage and the possible risk factors that influence bone mineral density (BMD) in this population.

METHODS

One hundred thirty-one elderly male patients with type 2 diabetes (73.12 +/- 5.54 years of age, diabetic duration 5.28 +/- 3.56 years, HbA(1C) 7.87% +/- 1.82 %), >65 years of age were recruited. All subjects were submitted to dual-energy X-ray absorptiometry to evaluate the BMD at lumbar spine (LS), femoral neck (FN), and femoral trochanter (FT). Fasting blood samples were taken to check hormones and biochemical levels. Demographic data were also collected.

RESULTS

In the different bone sites studied, the percentage of osteoporosis and osteopenia varied in this group of patients ranging from 29.0 to 31.3% and 29.0 to 33.6%, respectively. Weight, HbA(1C), body mass index, and testosterone were correlated with BMD at all the bone sites studied. Weight was the best predictor among the above parameters for BMD by linear regression analysis at LS and FN, whereas testosterone was the best predictor for BMD at FT.

CONCLUSIONS

In the different bone sites studied, the percentage of osteoporosis and osteopenia varied ranging from 29.0 to 31.3% and 29.0 to 33.6%, respectively. Weight was the best predictor for BMD at LS and FN and testosterone was the best predictor for BMD at FT. Poor glycemic control was correlated with osteoporosis.

Diet, nutrition and the prevention of osteoporosis

Objective:

To review the evidence on diet and nutrition relating to osteoporosis and provide recommendations for preventing osteoporosis, in particular, osteopototic fracture.

Approach:

Firstly, to review the definition, diagnosis and epidemiology of osteoporosis, to discuss the difficulties in using bone mineral density to define osteoporosis risk in a world-wide context and to propose that fragility fracture should be considered as the disease endpoint. Secondly, to provide an overview of the scientific data, the strengths and weaknesses of the evidence and the conceptual difficulties in interpreting studies linking diet, nutrition and osteoporosis. The following were considered: calcium, vitamin D, phosphorus, magnesium, protein and fluorine. Other potential dietary influences on bone health were also discussed, including vitamins, trace elements, electrolytes, acid–base balance, phyto-oestrogens, vegetarianism and lactose intolerance.

Conclusions:

There is insufficient knowledge linking bone mineral status, growth rates or bone turnover in children and adolescents to long-term benefits in old age for these indices to be used as markers of osteoporotic disease risk. For adults, the evidence of a link between intakes of any dietary component and fracture risk is not sufficiently secure to make firm recommendations, with the exception of calcium and vitamin D. For other aspects of the diet, accumulating evidence suggests that current healthy-eating advice to decrease sodium intake, to increase potassium intake, and to consume more fresh fruits and vegetables is unlikely to be detrimental to bone health and may be beneficial.

Serum 25-hydroxyvitamin D, parathyroid hormone, and bone mineral density in men: the Rancho Bernardo study

INTRODUCTION

This study examined the distribution and determinants of serum 25-hydroxyvitamin D (25OHD) and parathyroid hormone (PTH) and their associations with bone mineral density (BMD) at the hip and spine in 414 older men (mean age 74 years) living in southern California.

METHODS

At a clinic visit (1997-2000), demographic and lifestyle information, fracture history, and medication use were recorded; venous blood for serum 25OHD and PTH was obtained; and BMD was measured at the hip and spine.

RESULTS

Only one man had vitamin D deficiency (25OHD <20 nmol/l), but 15.5% of the men had high parathyroid levels (PTH >or=65 pg/ml). The mean 25OHD and PTH levels were 109.0 nmol/l and 50.3 pg/ml, respectively. Overall, 21.5% used calcium and 9.7% used vitamin D supplements. Serum 25OHD decreased with age and was lowest in the winter; levels were higher in supplement users (vitamin D and/or calcium; p<0.01). Serum PTH did not vary by age or season, and it was lower in supplement users (p<0.01). After excluding 12 men who were outliers for serum 25OHD and PTH, there was no significant correlation between serum 25OHD and PTH (r=-0.05, p=0.3). In multiple adjusted models, serum 25OHD was positively associated with BMD at the hip (p=0.01) and spine (p=0.001). Serum PTH was moderately and inversely associated with BMD at the hip (p=0.04) but not at the spine (p=0.77).

CONCLUSION

We conclude that serum 25OHD is associated with bone health in older, community-dwelling men.

What is the influence of weight change on forearm bone mineral density in peri- and postmenopausal women? The health study of Nord-Trondelag, Norway

Weight loss in the elderly increases bone loss and the risk of fractures, especially at the hip and spine. The influence of weight change on non-weight-bearing parts of the skeleton is less well known. The purpose of this study was to investigate an association between weight change during the peri- and postmenopausal years and forearm bone mineral density (BMD). Among 8,856 women aged 45-60 years attending the first Health Study of Nord-Trøndelag, Norway (HUNT I, 1984-1986), a random sample of 2,795 women was invited to forearm densitometry (single x-ray absorptiometry technology) at HUNT II (1995-1997), after a mean period of 11.3 years. A total of 2,005 women (mean age: 65.1 years) were eligible. The mean weight had increased 3.4 kg; the gain was greater in the youngest women. A total of 382 women (19.1%) had lost and 1,331 women (66.3%) had gained weight. Weight change explained little of the BMD variance, 0.7% and 0.4% for weight loss and weight gain, respectively. Weight loss was an independent and statistically significant negative predictor of BMD, adjusted for body weight, age, age at menopause, smoking, and ovarian hormone treatment, particularly among women with a baseline body mass index greater than 25 kg/m2. No independent association between weight gain and forearm BMD was found.

Direct effects of caffeine on osteoblastic cells metabolism: the possible causal effect of caffeine on the formation of osteoporosis

BACKGROUND

Caffeine consumption has been reported to decrease bone mineral density (BMD), increase the risk of hip fracture, and negatively influence calcium retention. In this study, we investigated the influence of caffeine on the osteoblasts behaviour.

METHOD

Osteoblasts derived from newborn Wistar-rat calvaria was used in this study. The effects of various concentrations of caffeine on bone cell activities were evaluated by using MTT assay. Alkaline phosphatase (ALP) staining, von Kossa staining and biochemical parameters including ALP, lactate dehydrogenase (LDH), prostaglandin E2 (PGE2) and total protein were performed at day 1, 3, and 7. DNA degradation analysis under the caffeine influence was also performed.

RESULTS AND DISCUSSION

The results showed that the viability of the osteoblasts, the formation of ALP positive staining colonies and mineralization nodules formation in the osteoblasts cultures decreased significantly in the presence of 10 mM caffeine. The intracellular LDH, ALP and PGE2 content decreased significantly, the LDH and PGE2 secreted into the medium increased significantly. The activation of an irreversible commitment to cell death by caffeine was clearly demonstrated by DNA ladder staining.

CONCLUSION

In summary, our results suggest that caffeine has potential deleterious effect on the osteoblasts viability, which may enhance the rate of osteoblasts apoptosis.

Kidney function predicts the rate of bone loss in older individuals: the Cardiovascular Health Study

BACKGROUND

Results of cross-sectional analyses of the association of kidney function with bone mineral density (BMD) have been conflicting. We examined the association of cystatin-C, a new marker of kidney function that is unrelated to lean mass, with initial and follow-up BMD, in an ancillary study of the Cardiovascular Health Study, a population-based cohort of individuals > or = 65 years old.

METHODS

Two years after measurement of cystatin-C and other covariates, the first BMD was measured in Pittsburgh, Pennsylvania and Davis, California, by using dual energy x-ray absorptiometry. Follow-up BMD was measured in Pittsburgh 4 years later. Associations of cystatin-C with initial BMD and the change in BMD (%/y) at the hip were examined with linear regression. Analyses were conducted separately for men and women.

RESULTS

In 1519 participants who had cystatin-C and initial BMD assessed, 614 had follow-up BMD. The percent annual change in BMD at the total hip by cystatin-C quartiles was -0.24, -0.13, -0.40, and -0.66%/y (first to fourth quartile) in women and -0.02, -0.30, -0.18, and -0.94%/y in men. After adjusting for potential confounders, cystatin-C was marginally associated with initial BMD in men but not women. Cystatin-C was associated with bone loss in men; after adjustment for weight loss, cystatin-C was not associated with bone loss in women.

CONCLUSION

Kidney dysfunction, as assessed by cystatin-C, is associated with a more rapid loss of BMD at the hip, especially in men. Further studies are needed to confirm these findings and to determine whether this loss leads to an elevated risk of fracture.

Coffee and health: a review of recent human research

Coffee is a complex mixture of chemicals that provides significant amounts of chlorogenic acid and caffeine. Unfiltered coffee is a significant source of cafestol and kahweol, which are diterpenes that have been implicated in the cholesterol-raising effects of coffee. The results of epidemiological research suggest that coffee consumption may help prevent several chronic diseases, including type 2 diabetes mellitus, Parkinson's disease and liver disease (cirrhosis and hepatocellular carcinoma). Most prospective cohort studies have not found coffee consumption to be associated with significantly increased cardiovascular disease risk. However, coffee consumption is associated with increases in several cardiovascular disease risk factors, including blood pressure and plasma homocysteine. At present, there is little evidence that coffee consumption increases the risk of cancer. For adults consuming moderate amounts of coffee (3-4 cups/d providing 300-400 mg/d of caffeine), there is little evidence of health risks and some evidence of health benefits. However, some groups, including people with hypertension, children, adolescents, and the elderly, may be more vulnerable to the adverse effects of caffeine. In addition, currently available evidence suggests that it may be prudent for pregnant women to limit coffee consumption to 3 cups/d providing no more than 300 mg/d of caffeine to exclude any increased probability of spontaneous abortion or impaired fetal growth.

Management of osteoporosis: a national survey of Israeli dietitians' knowledge and perceptions

The aim of this study was to assess Israeli dietitians' knowledge and attitudes regarding osteoporosis. Participants were 320 dietitians responding to a mail survey. Israeli dietitians scored highly on the Facts on Osteoporosis Quiz-FOOQ. Israeli dietitians' dietary knowledge regarding calcium (recommended dietary allowance, content in food and in supplements) was fairly high; unlike knowledge regarding vitamin D. Israeli dietitians had a firm positive opinion of their role in the prevention and treatment of osteoporosis.

Lifelong risk factors for osteoporosis and fractures in elderly women with low body mass index--a population-based study

Low body weight is associated with an increased risk for osteoporosis and fractures, but the contribution of other lifestyle related factors have not been previously studied within lean elderly women. The present study evaluated the association between lifelong lifestyle factors and bone density, falls and postmenopausal fractures in elderly women with low body mass index (BMI). A population-based sample of 1,222 women aged 70 to 73 years was stratified by BMI tertiles, and all 407 women in the lowest tertile participated. Data on falls and postmenopausal fractures, physical activity, functional capacity, calcium intake, smoking, alcohol intake and medical factors at different ages were obtained by a questionnaire. Calcaneum bone mass as broadband ultrasound attenuation (BUA) was assessed with a quantitative ultrasound (QUS) device, and bone mineral density (BMD) at the distal radius was measured with a dual-energy X-ray absorptiometry (DXA). Low current physical activity was associated with lower calcaneum BUA and factors associated with higher BUA were body weight, low lifetime occupational physical activity, hormone replacement and type 2 diabetes. Weight, type 2 diabetes and thiatzide use were associated with higher radius BMD. The final multivariate model consisted of four independent factors associated with fractures: low lifetime habitual physical activity (OR 3.7, 95% CI 1.9-7.1), diabetes (OR 0.2, 95% CI 0.1-1.0), living alone (OR 1.7, 95% CI 1.0-3.0) and calcaneum BUA (1.8, 95% CI 1.3-2.4). Poor functional ability and symptoms of depression were associated with recent falling. In elderly women with low BMI, lifelong physical activity may protect from fractures, while low calcaneum bone mass and living unpartnered appear to be associated with an increased risk for fractures. Poor functional ability and presence of depression may be associated with risk of falling. Type 2 diabetes may modify the risk of low bone mass and low-trauma postmenopausal fractures. Albeit that the results of this study need to be confirmed in prospective follow-up studies, multifactorial program with the emphasis on physical and social activation in the primary care setting for preventing falls and fractures in lean elderly women is recommended.

Bone mineral density is not reduced in HIV-infected Caucasian men treated with highly active antiretroviral therapy

OBJECTIVE

Recent studies have reported low bone mineral density (BMD) in patients infected with human immunodeficiency virus (HIV). Frequently these findings have been attributed to treatment with highly active antiretroviral therapy (HAART). We sought to determine whether BMD in HIV-infected men treated with HAART for at least 3 months is different from that in healthy controls, and, if so, what HIV-related factors might explain this finding.

DESIGN

Cross-sectional analysis.

PATIENTS

Fifty-nine HIV-infected Caucasian men treated with HAART, and 118 healthy community-dwelling controls. Each HIV-infected man was age-matched (within 5 years) to two controls.

MEASUREMENTS

All participants had measurements of BMD and bone-related laboratory parameters.

RESULTS

The mean duration of known HIV infection was 8.5 years, and of treatment with HAART was 52 months. There was no significant difference in mean BMD between groups at the lumbar spine (HIV group: 1.23 g/cm2, controls: 1.25 g/cm2; P = 0.53) or total body (HIV group: 1.18 g/cm2, controls: 1.20 g/cm2; P = 0.09). At the total hip the HIV-infected group had significantly lower BMD than the control group (HIV group: 1.03 g/cm2, controls: 1.09 g/cm2; P = 0.01). The HIV-infected group were, on average, 6.3 kg lighter than the controls. After adjusting for this weight difference, HIV infection was not an independent predictor of BMD at any site (lumbar spine P = 0.79; total hip P = 0.18; total body P = 0.76).

CONCLUSIONS

HIV-infected men treated with HAART are lighter than healthy controls. This weight difference is responsible for a small decrement in hip BMD. Overall, BMD is not significantly reduced in HIV-infected Caucasian men treated with HAART.

Incidence and risk factors for vertebral fracture in women and men: 25-year follow-up results from the population-based Framingham study

This study evaluates baseline characteristics of 704 women and men in the Framingham Study with respect to long-term risk of incident vertebral fracture. Incidence was 24% in women and 10% in men. Few factors in middle-aged persons, except prevalent (moderate) fracture and alcohol consumption (in men), predicted long-term incidence of vertebral fracture.

INTRODUCTION

We studied potential risk factors in women and men in middle adult years to help identify individuals at increased long-term risk of vertebral fracture in advanced age.

MATERIALS AND METHODS

Participants included Framingham cohort members who underwent radiographic examinations at baseline in 1967-1969 (mean age, 53 years) and follow-up in 1992-1993. Semiquantitative methods were used to determine incident fracture, defined as any vertebral body graded normal at baseline and at least mildly deformed (20-25% reduction or more in any vertebral height) at follow-up. Information on potential risk factors was obtained from examinations conducted at or before baseline radiography.

RESULTS

Prevalence of vertebral fracture was similar (14%) in women and men, although incidence was greater in women (24%) than men (10%). Alcohol consumption increased fracture risk in men. Multivariable-adjusted ORs increased from 1.78 in men who consumed 1-3 oz of alcohol per week in middle-age years to 4.61 in those with intakes of > or =4 oz/week (trend, P = 0.0099). Age, height, weight, grip strength, physical activity, metacarpal cortical area, and estrogen use (in women) had little or no influence on cumulative incidence of vertebral fracture. Results were similar when fracture was restricted to (at least) moderate severity; however, participants with moderate to severe fracture prevalent at baseline had five times the incidence of moderate to severe fracture during follow-up compared with those without moderately to severe prevalent fractures.

CONCLUSIONS

Few factors in middle-aged persons, except prevalent fracture and alcohol consumption (in men), predict long-term incidence of vertebral fracture. The explanation underlying this finding is not readily apparent, however, risk factors for vertebral fracture may be more relevant to older individuals, with respect to short-term fracture risk, than to middle-aged adults in relation to long-term risk with aging.

Biological effects of conjugated linoleic acids in health and disease

Conjugated linoleic acid (CLA) is a mixture of positional and geometric isomers of octadecadienoic acid [linoleic acid (LA), 18:2n-6] commonly found in beef, lamb and dairy products. The most abundant isomer of CLA in nature is the cis-9, trans-11 (c9t11) isomer. Commercially available CLA is usually a 1:1 mixture of c9t11 and trans-10, cis-12 (t10c12) isomers with other isomers as minor components. Conjugated LA isomer mixture and c9t11 and t10c12 isomers alone have been attributed to provide several health benefits that are largely based on animal and in vitro studies. Conjugated LA has been attributed many beneficial effects in prevention of atherosclerosis, different types of cancer, hypertension and also known to improve immune function. More recent literature with availability of purified c9t11 and t10c12 isomers suggests that t10c12 is the sole isomer involved in antiadipogenic role of CLA. Other studies in animals and cell lines suggest that the two isomers may act similarly or antagonistically to alter cellular function and metabolism, and may also act through different signaling pathways. The effect of CLA and individual isomers shows considerable variation between different strains (BALB/C mice vs. C57BL/6 mice) and species (e.g., rats vs. mice). The dramatic effects seen in animal studies have not been reflected in some clinical studies. This review comprehensively discusses the recent studies on the effects of CLA and individual isomers on body composition, cardiovascular disease, bone health, insulin resistance, mediators of inflammatory response and different types of cancer, obtained from both in vitro and animal studies. This review also discusses the latest available information from clinical studies in these areas of research.

Trabecular bone status in ultradistal tibia under habitual gait loading: a pQCT study in postmenopausal women

This study investigated regional volumetric trabecular bone mineral density (tBMD) and bone area at the ultradistal tibia in Chinese women using peripheral quantitative computed tomography. Fifty-six postmenopausal women aged 47-62 yr participated in BMD measurements at baseline and 22 of them were followed at both 1-yr and 3-yr follow-up scans. Regional baseline tBMD, rate of annual bone loss, and trabecular bone area were determined. Baseline measurements showed that the tBMD of both the posterior (252.9+/-63.4 mg/cm(3)) and medial (226.6+/-68.9 mg/cm(3)) regions was significantly higher than that of the anterior (126.3+/-61.9 mg/cm(3)) and lateral regions (149.8+/-50.6 mg/cm(3)), respectively (p<0.001). Both the 1-yr and 3-yr follow-up measurements showed that there was significant physiological annual tBMD loss on an average of 1.61%, at the four regions. Inter-slice regional tBMD and trabecular bone area measurements demonstrated a significant linear decrease from the distal to proximal aspects (p<0.001). Findings suggest that dynamic compressive loading during the heel strike and the body weight vector shifting toward the medial aspect during the stance phase in a normal gait might account for the regional tBMD differences. Increased tBMD and bone area toward the distal tibial endplate may adapt to withstand the axial impact loading. However, the low-impact weight-bearing nature of a normal gait may not be osteogenic to prevent regional bone loss. An exercise program specific to the women at risk should be contemplated.

Effects of conjugated linoleic acid and exercise on bone mass in young male Balb/C mice

There is an increase in obesity among the population of industrialized countries, and dietary supplementation with Conjugated Linoleic Acid (CLA) has been reported to lower body fat mass. However, weight loss is generally associated with negative effects on bone mass, but CLA is reported to have beneficial effects on bone. Furthermore, another factor that is well established to have a beneficial effect on bone is exercise (EX). However, a combination therapy of CLA and EX on bone health has not been studied. In this paper, we report the beneficial effects of CLA and EX on bone, in four different groups of Balb-C young, male mice. There were 4 groups in our study: 1. Safflower oil (SFO) sedentary (SED); 2. SFO EX; 3. CLA SED; 4. CLA EX. Two months old mice, under their respective treatment regimens were followed for 14 weeks. Mice were scanned in vivo using a DEXA scanner before and after treatment. At the end of the treatment period, the animals were sacrificed, the left tibia was removed and scanned using peripheral quantitative computerized tomography (pQCT). The results showed that although CLA decreased gain in body weight by 35%, it however increased bone mass by both reducing bone resorption and increasing bone formation. EX also decreased gain in body weight by 21% and increased bone mass; but a combination of CLA and EX, however, did not show any further increase in bone mass. In conclusion, CLA increases bone mass in both cancellous and cortical bones, and the effects of CLA on bone is not further improved by EX in pure cortical bone of young male mice.

Alcohol-induced bone loss and deficient bone repair

BACKGROUND

Chronic consumption of excessive alcohol eventually results in an osteopenic skeleton and increased risk for osteoporosis. Alcoholics experience not only increased incidence of fractures from falls, but also delays in fracture healing compared with non-alcoholics. In this review the term "alcohol-induced bone disease" is used to refer to these skeletal abnormalities. Alcohol-induced osteopenia is distinct from osteoporoses such as postmenopausal osteoporosis and disuse osteoporosis. Gonadal insufficiency increases the rate of bone remodeling, whereas alcohol decreases this rate. Thus, histomorphometric studies show different characteristics for the bone loss that occurs in these two disease states. In particular, alcohol-induced osteopenia results mainly from decreased bone formation rather than increased bone resorption. Human, animal and cell culture studies of the effects of alcohol on bone strongly suggest alcohol has a dose-dependent toxic effect on osteoblast activity. The capacity of bone marrow stromal cells to differentiate into osteoblasts has a critical role in the cellular processes involved in the maintenance of the adult human skeleton by bone remodeling. Chronic alcohol consumption suppresses osteoblastic differentiation of bone marrow cells and promotes adipogenesis. In fracture healing, the effect of alcohol is to suppress synthesis of an ossifiable matrix, possibly due to inhibition of cell proliferation and maldifferentiation of mesenchymal cells in the repair tissue. This results in the deficient bone repair observed in animal studies, characterized by repair tissue of lower stiffness, strength and mineral content. Current knowledge of cellular effects and molecular mechanisms involved in alcohol-induced bone disease is insufficient to develop interventional strategies for its prevention and treatment.

OBJECTIVES

The objectives of this review are 1) to identify the characteristics of alcohol-induced bone loss and deficient bone repair as revealed in human and animal studies, 2) to determine the current understanding of the cellular effects underlying both skeletal abnormalities, and 3) to suggest directions for future studies to resolve current ambiguities regarding the cellular basis of alcohol-induced bone disease.

Variables for the prediction of femoral bone mineral status in American women

INTRODUCTION

A reliable procedure for identifying persons at risk for osteoporosis and subsequent fracture is needed so that preventive measures may be initiated.

MATERIAL AND METHODS

Participants included 7,532 women, ages 20 and older, surveyed in the National Health and Nutrition Examination Survey III (NHANES, 1988-1994). Influences of race, body composition, exercise, alcohol intake, smoking status, as well as the effect of nutritional intake of calcium, phosphorus, magnesium, iron, zinc, sodium, and potassium on bone mineral density (BMD) were assessed.

RESULTS

Advancing age, low body weight, low exercise expenditure, and smoking were significant predictors for low BMD. Nutritional variables examined were not significant in the predictive models.

CONCLUSIONS

The absence of calcium from the predictive models indicates the need for re-evaluation of the current recommended intake levels of this nutrient. A greater emphasis on factors such as exercise and achieving adequate weight is recommended.

DISCUSSION

Providing women with the knowledge of their risk for low BMD may influence lifestyle behaviors, which may ultimately result in the prevention of bone injury.

Longitudinal changes in forearm bone mineral density in women and men aged 45-84 years: the Tromso Study, a population-based study

The aim of this study was to describe changes in bone mineral density in Norwegian women and men aged 45-84 years in a population-based, longitudinal study. Bone mineral density (g/cm2) was measured at distal and ultradistal forearm sites with single x-ray absorptiometric devices in 3,169 women and 2,197 men at baseline in 1994-1995 and at follow-up in 2001 (standard deviation, 0.4 years). The mean annual bone loss was -0.5% and -0.4% in men and -0.9% and -0.8% in women not using hormone replacement therapy at the distal and ultradistal sites, respectively. In men, age was a negative predictor of bone mineral density change at both sites. Women not using hormone replacement therapy had the highest bone loss at the ultradistal site 1-5 years after menopause. The correlation between the two measurements was high: r = 0.93 and r = 0.90 in women and r = 0.96 and r = 0.93 in men for the distal and ultradistal sites, respectively. More than 70% kept their quartile positions, indicating a high degree of tracking of bone mineral density measurements. Although the study population live above the polar circle, the rate of bone loss was not higher at the distal and ultradistal forearm sites compared with that of other cohorts.

Epidemiology, etiology, and diagnosis of osteoporosis

Osteoporosis, a major public health problem, is becoming increasingly prevalent with the aging of the world population. Osteoporosis is a skeletal disorder characterized by compromised bone strength, which predisposes the individual to an increased risk of fractures of the hip, spine, and other skeletal sites. The clinical consequences and economic burden of this disease call for measures to assess individuals who are at high risk to allow for appropriate intervention. Many risk factors are associated with osteoporotic fracture, including low peak bone mass, hormonal factors, the use of certain drugs (eg, glucocorticoids), cigarette smoking, low physical activity, low intake of calcium and vitamin D, race, small body size, and a personal or a family history of fracture. All of these factors should be taken into account when assessing the risk of fracture and determining whether further treatment is required. Because osteoporotic fracture risk is higher in older women than in older men, all postmenopausal women should be evaluated for signs of osteoporosis during routine physical examinations. Radiologic laboratory assessments of bone mineral density generally should be reserved for patients at highest risk, including all women over the age of 65, younger postmenopausal women with risk factors, and all postmenopausal women with a history of fractures. The evaluation of biochemical markers of bone turnover has been useful in clinical research. However, the predictive factor of these measurements is not defined clearly, and these findings should not be used as a replacement for bone density testing. Together, clinical assessment of osteoporotic risk factors and objective measures of bone mineral density can help to identify patients who will benefit from intervention and, thus, can potentially reduce the morbidity and mortality associated with osteoporosis-associated fractures in this population.

Epidemiology of osteoporosis

Osteoporosis and related fractures represent a major, and growing, public health concern for the United States and worldwide. The pathogenesis of osteoporosis is complex, requiring attention to the different life phases involved in growth, maintenance, and loss of bone, in addition to non-skeletal factors associated with falls and fractures. While the current clinical definition is based upon bone density measurements, other determinants of skeletal strength, particularly bone quality, are important to identify for future areas of research and prevention efforts. This epidemiologic review describes the definition, pathogenesis, and risk factors, as well as the frequency and impact of osteoporosis, with particular emphasis upon hip fracture.

Immobilization decreases duodenal calcium absorption through a 1,25-dihydroxyvitamin D-dependent pathway

Immobilization induces significant and progressive bone loss, with an increase in urinary excretion and a decrease in intestinal absorption of calcium. These actions lead to negative calcium balance and the development of disuse osteoporosis. The aims of this study were to evaluate the molecular mechanisms of decreased intestinal calcium absorption and to determine the effect of dietary 1,25-dihydroxyvitamin D [1,25(OH)2D] and a high-calcium diet on bone loss due to immobilization. The immobilized rat model was developed in the Bollman cage III to induce systemic disuse osteoporosis in the animals. There was a significant decrease in lumbar bone mineral density (BMD) and intestinal calcium absorption in the immobilized group compared with the controls. Serum 25-hydroxyvitamin D concentration did not change, but 1,25(OH)2D concentration decreased significantly. The mRNA levels of renal 25-hydoxyvitamin D 24-hydroxylase (24OHase) increased, whereas those of renal 25-hydroxyvitamin D 1-alpha hydroxylase (1alpha-hydroxylase), duodenal transient receptor potential cation channel, subfamily V, member 6 (TRPV6), TRPV5, and calbindin-D9k were all decreased. A high-calcium diet did not prevent the reduction in lumbar BMD or affect the mRNA expression of proteins related to calcium transport. Dietary administration of 1,25(OH)2D increased the intestinal calcium absorption that had been downregulated by immobilization. TRPV6, TRPV5, and calbindin-D9k mRNA levels were also upregulated, resulting in prevention of the reduction in lumbar BMD. Therefore, it is concluded that dietary 1,25(OH)2D prevented decreases in intestinal calcium absorption and simultaneously prevented bone loss in immobilized rats. However, it remains unclear that calcium absorption and expression of calcium transport proteins are essential for the regulation of lumbar BMD.

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.

Endogenous sex steroids, weight change and rates of hip bone loss in older men: the MrOS study

INTRODUCTION

Lower levels of endogenous sex steroids or declines in these hormones may contribute to the increased rates of bone loss observed in older adults experiencing weight loss. We hypothesized that among older men with weight loss, higher rates of bone loss at the hip would be observed in men with lower baseline bioavailable sex steroids or those with greater declines in these hormones.

METHODS

To test this hypothesis, body weight, hip bone mineral density (BMD) using dual energy x-ray absorptiometry and endogenous sex steroids in paired serum samples by sensitive immunoassays were measured at a baseline and at a second examination that was held an average of 1.8 years later in 1267 older men enrolled in the Osteoporotic Fractures in Men (MrOS) study.

RESULTS

Men experiencing weight loss had higher rates of hip bone loss than those with stable weight or weight gain within each quartile of baseline sex steroid level [p values for test of trend across weight change categories <0.010 within each quartile of bioavailable estradiol and testosterone and <0.060 within each quartile of sex hormone-binding globulin (SHBG)]. Results were similar when a change in sex steroids was substituted for baseline sex steroids in the analyses. Among men with weight loss, the rate of decline in total hip BMD showed a stepwise increase in magnitude with decreasing baseline bioavailable estradiol (p value for trend <0.040), with increasing baseline SHBG (p value for trend<0.030) and with greater decreases in bioavailable testosterone from baseline (p value for trend <0.001).

CONCLUSIONS

These findings support the hypothesis that the impact of weight loss in older men on rates of hip bone loss may be increased by the presence of a sex steroid insufficiency.

Correlations between bone mineral density and demographic, lifestyle, and biochemical variables in community-dwelling Japanese women 69 years of age and over

INTRODUCTION

A few epidemiologic studies have comprehensively attempted to identify risk factors for low bone mineral density (BMD) in elderly Asian women. The purpose of this study was to identify demographic, lifestyle, and biochemical factors correlated with BMD in elderly Japanese women 69 years of age and over.

METHODS

The study design was cross-sectional. The subjects were 583 ambulatory women aged 69 years and over, and their average age was 74.3 (SD 4.4) years. Predictor variables were age, reproductive history, anthropometric indices, grip strength, calcium intake, lifestyle information, and serum 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D (1,25(OH)(2)D), osteocalcin (OC), and undercarboxylated osteocalcin (ucOC) values. The outcome variable was forearm BMD measured with a DTX-200 osteometer.

RESULTS

Simple linear regression analyses showed that BMD was significantly positively associated with body height, weight, body mass index, grip strength, serum albumin concentration, and "housework," and negatively associated with age, years since menopause, age at menarche, number of children, serum 1,25(OH)(2)D concentration, serum OC concentration, and ucOC concentration. The stepwise multiple regression analysis showed that weight (beta=0.00316, SE=0.00028, R(2)=0.180), age (beta=-0.00321, SE=0.00050, R(2)=0.108), log-transformed serum OC (beta=-0.0445, SE=0.0064, R(2)=0.053), log-transformed serum 1,25(OH)(2)D (beta=-0.0401, SE=0.0074, R(2)=0.050), "farmwork" (beta=0.00904, SE=0.00426, R(2)=0.005), and serum 25(OH)D concentration (beta=0.000281, SE=0.000120, R(2)=0.003) were significantly associated with BMD.

CONCLUSION

It was concluded that body weight is a major predictor of forearm BMD among the factors measured in this study in independent Japanese women 69 years of age and over and that serum 1,25(OH)(2)D concentration may be associated with cortical BMD. Maintenance of body weight is very important for maintaining BMD in this population, unless a large weight aggravates obesity-related diseases. A follow-up study is needed to confirm these findings.

Long-term recreational gymnastics provides a clear benefit in age-related functional decline and bone loss. A prospective 6-year study

INTRODUCTION

Bone fragility and decreased functional performance are risk factors for osteoporotic fractures. The influence of long-term recreational gymnastics on the maintenance of bone rigidity and physical performance was evaluated.

METHODS

One hundred and seven gymnasts and 110 referents (93% of the original sample) participated in this 6-year prospective study. Analysis of covariance (ANCOVA) was used to estimate the between-group differences and changes by time, and regression analyses to find predictors for changes.

RESULTS

In both groups agility and leg extensor power decreased by over 3% and 10%, respectively, but the original between-group differences, favoring the gymnasts, persisted. Proximal femur bone mineral content (BMC) decreased approximately 0.5% per year in both groups, and femoral neck section modulus decreased. Trabecular density of the distal tibia declined only marginally, and cortical area of the tibial midshaft remained unchanged, while cortical density decreased about 2% in both groups. After adjustment by age, height, weight, change in weight, and follow-up time, antiresorptive medication and high calcium intake accounted most for the maintenance of bone rigidity.

CONCLUSIONS

In spite of similar rates of decline in bone characteristics and physical performance, the recreational gymnasts' overall physical condition was comparable to the level that their less active referents had shown approximately 5 years earlier.

Utility of screening tools for the prediction of low bone mass in African American men

INTRODUCTION

Osteoporosis remains under-diagnosed, particularly in African American men, despite the availability of reliable diagnostic tests. In women, several screening tools, including heel ultrasound and clinical assessment tools, reliably predict low bone mass, however the usefulness of these screening tools in African American men is unknown. The aim of this study was to determine the utility of screening tools, namely heel ultrasound, the osteoporosis self-assessment tool (OST), weight-based criterion (WBC) and body mass index (BMI), in screening for low bone mass in African American men.

MATERIALS AND METHODS

African American men 35 years of age and older were invited to participate. The OST risk index is a score based on age and weight [(weight in kilograms--age in years)x0.2]. Bone mineral density (BMD) of the heel was measured by heel ultrasound, and BMD of both the lumbar spine and hip were determined by dual energy X-ray absorptometry (DXA). One hundred and twenty-eight men fulfilled the inclusion criteria for our study.

RESULTS

The population prevalence of osteopenia and osteoporosis were 39% and 7%, respectively. Using a heel ultrasound T-score cut-off value of -1 or less, we predicted low bone mass (T-score of -2 or less at the hip) with a sensitivity of 83%, a specificity of 71% and an area under the curve (AUC) of 0.80. Using an OST cut-off value of 4, we predicted low bone mass with a sensitivity of 83%, a specificity of 57% and an AUC of 0.83. The OST risk index ranged from 18.1 to -6.1, based on which we categorized risk as: low, 5 or greater; moderate, 0-4; high, -1 or less. Of the men with a high-risk OST score, 87% had either osteopenia or osteoporosis based on World Health Organization (WHO) criteria. Using the WBC alone with a cut-off value of 85 kg, we predicted low bone mass with a sensitivity of 74%, a specificity of 50% and an AUC of 0.70. A BMI cut-off value of 30 or greater yielded a sensitivity of 83%, a specificity of 43% and an AUC of 0.70 for the diagnosis of low bone mass.

DISCUSSION

The prevalence of osteopenia and osteoporosis were unexpectedly high in outpatient African American male veterans, who are considered to be at low risk for low bone mass. Heel ultrasound was able to predict low bone mass with sufficiently high sensitivity and specificity for use as a screening tool. Surprisingly, WBC and BMI proved ineffective in predicting low bone mass with adequate sensitivity and specificity. The OST, a clinical formula based on weight and age, appeared to be an easy and reliable screening tool for identifying men at high risk for low bone mass.

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.

Ablation of the Sam68 RNA binding protein protects mice from age-related bone loss

The Src substrate associated in mitosis of 68 kDa (Sam68) is a KH-type RNA binding protein that has been shown to regulate several aspects of RNA metabolism; however, its physiologic role has remained elusive. Herein we report the generation of Sam68-null mice by homologous recombination. Aged Sam68^−/− mice preserved their bone mass, in sharp contrast with 12-month-old wild-type littermates in which bone mass was decreased up to approximately 75%. In fact, the bone volume of the 12-month-old Sam68^−/− mice was virtually indistinguishable from that of 4-month-old wild-type or Sam68^−/− mice. Sam68^−/− bone marrow stromal cells had a differentiation advantage for the osteogenic pathway. Moreover, the knockdown of Sam68 using short hairpin RNA in the embryonic mesenchymal multipotential progenitor C3H10T1/2 cells resulted in more pronounced expression of the mature osteoblast marker osteocalcin when differentiation was induced with bone morphogenetic protein-2. Cultures of mouse embryo fibroblasts generated from Sam68^+/+ and Sam68^−/− littermates were induced to differentiate into adipocytes with culture medium containing pioglitazone and the Sam68^−/− mouse embryo fibroblasts shown to have impaired adipocyte differentiation. Furthermore, in vivo it was shown that sections of bone from 12-month-old Sam68^−/− mice had few marrow adipocytes compared with their age-matched wild-type littermate controls, which exhibited fatty bone marrow. Our findings identify endogenous Sam68 as a positive regulator of adipocyte differentiation and a negative regulator of osteoblast differentiation, which is consistent with Sam68 being a modulator of bone marrow mesenchymal cell differentiation, and hence bone metabolism, in aged mice.

Osteoporosis is a debilitating bone disease that is characterized by reduced bone mass and microarchitectural damage, which result in increased bone fragility and susceptibility to fracture. Peak bone mass, which is achieved by the age of 30 in humans, has been identified as a major determinant of resistance or susceptibility to osteoporosis. The authors generated mice deficient for the Sam68 RNA binding protein, a protein of unknown physiologic function. The mice develop normally and are protected against bone loss during aging. Age-related bone loss has long been associated with an increase in marrow adipocytes, which are derived from the same mesenchymal lineage as osteoblasts in bone marrow. The authors showed that Sam68 regulates the differentiation of this mesenchymal lineage, such that in its absence, osteoblasts continued to be generated in aging bone, leading to preservation of bone mass. This study identifies a physiologic role for Sam68 as a modulator of the bone marrow stem cell niche and hence of bone metabolism. The data identify Sam68 as a potential therapeutic target for the prevention and treatment of age-related bone loss.