Determinants of peak bone mass

The Effect of the Supplementation of a Diet Low in Calcium and Phosphorus with Either Sheep Milk or Cow Milk on the Physical and Mechanical Characteristics of Bone using A Rat Model

This study assessed the effect of cow milk (CM) and sheep milk (SM) consumption on the micro-structure, mechanical function, and mineral composition of rat femora in a male weanling rat model. Male weanling rats were fed a basal diet with a 50% reduction in calcium and phosphorus content (low Ca/P-diet) supplemented with either SM or CM. Rats were fed for 28 days, after which the femora were harvested and stored. The femora were analyzed by μ-CT, three-point bending, and inductively coupled plasma-mass spectrometry (ICP-MS). The addition of either milk to the low Ca/P-diet significantly increased (p < 0.05) trabecular bone volume, trabecular bone surface density, trabecular number, cortical bone volume, and maximum force, when compared to rats that consumed only the low Ca/P-diet. The consumption of either milk resulted in a significant decrease (p < 0.05) in trabecular pattern factor, and cortical bone surface to volume ratio when compared to rats that consumed only the low Ca/P-diet. The results were achieved with a lower consumption of SM compared to that of CM (p < 0.05). This work indicates that SM and CM can help overcome the effects on bone of a restriction in calcium and phosphorus intake.

Sex dimorphic regulation of osteoprogenitor progesterone in bone stromal cells

Increasing peak bone mass is a promising strategy to prevent osteoporosis. A mouse model of global progesterone receptor (PR) ablation showed increased bone mass through a sex-dependent mechanism. Cre-Lox recombination was used to generate a mouse model of osteoprogenitor-specific PR inactivation, which recapitulated the high bone mass phenotype seen in the PR global knockout mouse mode. In this work, we employed RNA sequencing analysis to evaluate sex-independent and sex-dependent differences in gene transcription of osteoprogenitors of wild-type and PR conditional knockout mice. PR deletion caused marked sex hormone-dependent changes in gene transcription in male mice as compared to wild-type controls. These transcriptional differences revealed dysregulation in pathways involving immunomodulation, osteoclasts, bone anabolism, extracellular matrix interaction and matrix interaction. These results identified many potential mechanisms that may explain our observed high bone mass phenotype with sex differences when PR was selectively deleted in the MSCs.

Peak Bone Mass and Patterns of Change in Total Bone Mineral Density and Bone Mineral Contents From Childhood Into Young Adulthood

The literature has not reached a consensus on the age when peak bone mass is achieved. This study examines growth patterns of total bone mineral content (TBMC) and total bone mineral density (TBMD), peak bone mass, effect of concurrent anthropometry measures, and physical activity on growth patterns in a sample of 312 white males and 343 females aged 8-30 yr. We analyzed data from participants enrolled in Fels Longitudinal Study. Descriptive analysis was used to ascertain characteristics of participants and growth patterns of TBMC and TBMD. Mixed effects models were applied to predict ages at attainment of peak TBMC and TBMD and assess the effects of height, weight, body mass index (BMI), and habitual physical activity on the attainment. Significant differences between sexes were observed for measures of TBMC and TBMD, and differences varied with age. For females, predicted median ages at peak TBMC and TBMD attainments are 21.96 yr (interquartile range [IQR]: 21.81-22.21) and 22.31 yr (IQR: 21.95-22.59), respectively. For males, predicted median ages are 23.34 yr (IQR: 24.34-26.19) and 26.86 yr (IQR: 25.14-27.98) respectively. For females, height, weight, and BMI, but not physical activity, had significant influences on attainment of TBMC and TBMD (p<0.01). For males, weight and BMI, but not height and physical activity, exerted significant influence on attainment of TBMC and TBMD (p<0.01), and also modified correlations between age and peak TBMC and TBMD. Our results suggest that (1) for both sexes, trajectories of TBMC and TBMD follow a curvilinear pattern between ages 8 and 30 yr; (2) predicted ages at peak TBMC and TBMD are from early to late 20s for both white males and females, with females reaching their peaks significantly earlier than males; and (3) concurrent height, weight, and BMI, but not habitual physical activity, exert significant effects on trajectories of TBMC and TBMD.

β-Ecdysone Augments Peak Bone Mass in Mice of Both Sexes

BACKGROUND

One of the strongest predictors for osteoporosis is peak bone mass. Interventions to augment peak bone mass have yet to be developed. β-Ecdysone (βEcd), a natural steroid-like compound produced by arthropods to initiate metamorphosis, is believed to have androgenic effects and so may be used to augment bone mass.

QUESTIONS/PURPOSES

The purpose of this study was to use both male and female (1) gonadal-sufficient; and (2) -insufficient mice to investigate sex differences in terms of bone development and structure after βEcd administration.

METHODS

Two-month-old male and female Swiss-Webster mice were randomized to receive either vehicle or βEcd (0.5 mg/kg) for 3 weeks. In a separate experiment to evaluate the effects of βEcd on sex hormone-deficient mice, gonadectomy was performed in male (orchiectomy [ORX]) and female mice (ovariectomy [OVX]). Sham-operated and the ORX/OVX mice were then treated for 3 weeks with βEcd. Primary endpoints for the study were trabecular bone structure and bone strength.

RESULTS

In male mice, the trabecular bone volume was 0.18±0.02 in the placebo-treated (PL) and 0.23±0.02 in the βEcd-treated group (p<0.05 versus PL); and 0.09±0.01 in the ORX group (p<0.05 versus PL) and 0.12±0.01 in the ORX+βEcd group. Vertebral bone strength (maximum load) was 43±2 in PL and 51±1 in the βEcd-treated group (p<0.05 versus PL); and 30±4 in the ORX group (p<0.05 versus PL) and 37±3 in the ORX+βEcd group. In female mice, trabecular bone volume was 0.23±0.02 in PL and 0.26±0.02 in the βEcd-treated group (p<0.05 versus PL); and 0.15±0.01 in the OVX group (p<0.05 versus PL) and 0.14±0.01 in the OVX+βEcd group. Maximum load of the vertebrae was 45±2 in PL and 48±4 in the βEcd-treated group; and 39±4 in the OVX group (p<0.05 versus PL) and 44±4 in the OVX+βEcd group.

CONCLUSIONS

These findings suggest the potential use of βEcd in the augmentation of bone mass in growing male and female mice. It may also partially prevent the detrimental effects of gonadectomy on trabecular bone.

CLINICAL RELEVANCE

Our results support the potential use of βEcd or nature products that are rich in βEcd to augment peak bone mass. βEcd may differ from the other anabolic hormone treatments that may have severe side effects such as serious cardiac complications. However, its effects on humans remain to be determined.

Age at First Delivery and Osteoporosis Risk in Korean Postmenopausal Women: The 2008-2011 Korea National Health and Nutrition Examination Survey (KNHANES)

It has been reported in several studies that there may be a significant correlation between reproductive history and the risk of osteoporosis due to the effect of estrogen. Under this hypothesis, however, it is unclear whether the age at first delivery has any major influences on the risk of osteoporosis. Therefore, this study aimed to investigate the relationship between the age at first delivery and the risk of osteoporosis in Korean menopausal women. This study was performed using data from the 2008–2011 Korea National Health and Nutrition Examination Survey and included 2,530 Korean postmenopausal women. The diagnosis of osteoporosis was made using the World Health Organization T-score criteria (T-score ≤ -2.5, at the femoral neck or lumbar spine). Participants were categorized into 3 groups according to age at first delivery: ≤23, 24–29, and ≥30 years. Older age, lower body mass index, lower calcium intake, later menarche, and earlier menopause increased the risk of osteoporosis, whereas hormone therapy and oral contraceptive use were associated with a decreased risk of osteoporosis. Postmenopausal women whose first delivery occurred at age 24–29 years were shown to have a significantly increased risk of osteoporosis (odds ratio, 2.124; 95% confidence interval, 1.096–4.113; P = 0.026) compared to those who first gave birth after the age of 30 years. These findings suggest that postmenopausal women whose first delivery occurred in their mid to late 20s, a period during which bone mass slowly accumulates to the peak, are at an increased risk of osteoporosis.

Cortical bone thickness can adapt locally to muscular loading while changing with age

Mechanical loading of muscle action is concentrated at muscle attachment sites; thus there may be a potential for site-specific variation in cortical bone thickness. Humeri from an early 20th-century Finnish (Helsinki) and two medieval English (Newcastle, Blackgate and York, Barbican) populations were subjected to pQCT scanning to calculate site-specific cross-sectional cortical bone area (CA) for four locations and to measure cortical thickness at muscle attachment sites and non-attachment sites. We found that CA at 80% of humerus length was significantly reduced compared to more distal cross-sections, which can be due to reduced stresses at the proximal shaft. The principal direction of loading at 80% humerus length was towards mediolateral plane, likely due to fixing the humerus close to the torso. At 35% the main direction of loading was towards anteroposterior plane, reflecting elbow flexing forces. The principal direction of loading varied between populations, sides and sexes at 50% humerus length due to preference between elbow and shoulder joint; thus this location might be useful when trying to infer differences in activity. These changes are likely due to overall shaft adaptation to forces acting at the humerus. In addition, we found a potential for site-specific variation in cortical thickness; cortical bone at muscle attachment sites was significantly thicker compared to non-attachment sites. Lastly, CA at 35% of humerus length and cortical thickness at non-attachment sites decreased with age. These results underline the importance of muscle loading for bone mass preservation as well as indicate that a site-specific variation of bone mass is possible.

Bone mineral density and vitamin D in PCOS and hirsutism

Polycystic ovary syndrome (PCOS) is the most frequent endocrinopathy in reproductive-aged women. The majority of hirsute patients are diagnosed with PCOS. Hyperandrogenemia, central obesity and insulin resistance may protect patients with PCOS from osteoporosis, whereas increased cortisol levels, low growth hormone and amenorrhea may be associated with decreased bone mineral density (BMD). Recent studies suggested that insulin resistance in PCOS is associated with decreased vitamin D levels that could not be explained by obesity alone. Vitamin D treatment may therefore have positive effects on insulin sensitivity and perhaps also hyperandrogenemia in patients with PCOS. In the present article, we review the evidence of changed BMD, bone mineral turnover and vitamin D status in PCOS and hirsutism compared with healthy women and the effects of medical intervention on BMD in PCOS.

Influence of heredity and environment on peak bone density: a review of studies in Croatia

One of the main determinants of who will develop osteoporosis is the amount of bone accumulated at peak bone density. There is poor agreement, however, on when peak bone density occurs. Ethnic differences were observed in age at peak bone density and their correlates. Since the diagnosis of osteoporosis and osteopaenia is based on the comparison between patients' bone mineral density (BMD) and optimal peak bone density in healthy young people (T-score), it is of great importance that each country should provide its own reference peak bone density data.This review article presents our published results on peak bone density in Croatia and compares them with findings in other populations. Our research included 18 to 25-year-old students from Zagreb University and their parents. The results showed that peak bone mass in young Croatian women was achieved before the age of twenty, but BMD continued to increase after the mid-twenties in the long-bone cortical skeleton. BMD was comparable to the values reported by the National Health and Nutrition Examination Survey (NHANES) and other studies that included the same age groups, except for the cortical part of the radius, where it was significantly lower. Men achieved peak bone density in the spine later than women, which cannot be explained by different diet or physical activity. As expected, heredity was more important for peak bone density than the environmental factors known to be important for bone health. However, the influence of heredity was not as strong as observed in most other populations. It was also weaker in the cortical than in the trabecular parts of the skeleton. Future research should include young adolescent population to define the exact age of achieving peak bone density in different skeletal sites.

Cross sectional properties of the human radial tuberosity

This study examines the cross sectional shape and biomechanical properties of the radial bone shaft at mid-radial tuberosity (RT) musculoskeletal marker (MSM). This information will provide insight into factors affecting bone modelling at muscle insertions. Radial shaft cross-sectional properties at radial tuberosity area (RTA) have not been previously studied. The material consists of 54 male skeletons derived from autopsies performed during the 1920s and 1930s and housed at the Central Natural History Museum, University of Helsinki. The age, sex and occupation of these individuals are known. We applied a pQCT (peripheral quantitative computed tomography) scan on the mid-site of the radial tuberosity to investigate the cross-sectional shape, the bone mineral density (BMD) and biomechanical properties. Our results indicate that bone modelling does not produce increased wall thickness or BMD at the RT site. Additionally we noticed that aging and physical activity affect the biomechanics of the RT and that the bone distribution at mid-RT is adapted to accommodate the biceps brachii muscle pull. We also found a clear association between RTA and biomechanical properties of mid-RT cross section.

Bone mineral density in adult survivors of childhood acute leukemia: impact of hematopoietic stem cell transplantation and other treatment modalities

Femoral and lumbar bone mineral densities (BMDs) were measured in 159 adults enrolled in the Leucémies de l'Enfant et de l'Adolescent program, a French prospective multicentric cohort of childhood leukemia survivors. BMDs were expressed as Z-scores, and multivariate linear regression analyses were used to construct association models with potential risk factors. Mean age at evaluation and follow-up was 23 and 14.7 years, respectively. In the whole cohort, mean femoral Z-score was -0.19 ± 0.08. Two factors were associated with lower femoral BMD transplantation (-0.49 ± 0.15 vs -0.04 ± 0.10 in the chemotherapy group; P = .006) and female sex (-0.34 ± 0.10 vs -0.03 ± 0.13; P = .03). Among patients who received a transplant, the only significant risk factor was hypogonadism (-0.88 ± 0.16 vs -0.10 ± 0.23; P = .04). A slight reduction in lumbar BMD (mean Z-score, -0.37 ± 0.08) was detected in the whole cohort without difference between the transplantation and chemotherapy groups. Among patients who received a transplant, younger age at transplantation was correlated with a low lumbar BMD (P = .03). We conclude that adults who had received only chemotherapy for childhood leukemia have a slight reduction in their lumbar BMD and a normal femoral BMD. Patients who received a transplant with gonadal deficiency have a reduced femoral BMD which might increase the fracture risk later in life.

Hypoestrogenism in young women and its influence on bone mass density

One of the most important hormonal factors responsible for bone health is estradiol. Genetic factors, adequacy of hormonal functioning, nutrition and physical activity may be the markers of bone status and development in young women. During adolescence, women reach peak bone acquisition and develop a skeletal mass. This process is largely regulated by endocrine factors mainly such as adequate levels of gonadal, adrenal and pituitary hormones. The crucial role played by estradiol and its impact on bones are very multiple. Estradiol induces growth factors' activation, receptor activator of nuclear factor kappa B ligand (RANKL) production inhibition and is mainly referred to antiresorptive activity. Clinical situations leading to hypoestrogenism has been linked to decreased bone mineral density leading to osteopenia and osteoporosis. This status both in fertile and perimenopausal women can increase the risk of pathological fractures. Such conditions as hypothalamic-pituitary insufficiency (functional hypothalamic amenorrhea, anorexia nervosa, Kallmann syndrome, hyperprolactinemia), ovarian failure (gonadal dysgenesis, premature ovarian failure) and iatrogenic treatment (surgery, chemotherapy, radiotherapy) can cause hypoestrogenism. The treatment of osteopenia and osteoporosis caused by hypoestrogenism is very essential and multidirectional. The crucial role of the therapy is the achievement of proper serum estradiol concentration and eliminate the causes of hypoestrogenism.

Inhibition of the progesterone nuclear receptor during the bone linear growth phase increases peak bone mass in female mice

Augmentation of the peak bone mass (PBM) may be one of the most effective interventions to reduce the risk of developing osteoporosis later in life; however treatments to augment PBM are currently limited. Our study evaluated whether a greater PBM could be achieved either in the progesterone nuclear receptor knockout mice (PRKO) or by using a nuclear progesterone receptor (nPR) antagonist, RU486 in mice. Compared to their wild type (WT) littermates the female PRKO mice developed significantly higher cancellous and cortical mass in the distal femurs, and this was associated with increased bone formation. The high bone mass phenotype was partially reproduced by administering RU486 in female WT mice from 1–3 months of age. Our results suggest that the inhibition of the nPR during the rapid bone growth period (1–3 months) increases osteogenesis, which results in acquisition of higher bone mass. Our findings suggest a crucial role for progesterone signaling in bone acquisition and inhibition of the nPR as a novel approach to augment bone mass, which may have the potential to reduce the burden of osteoporosis.

The mode of school transportation in pre-pubertal children does not influence the accrual of bone mineral or the gain in bone size--two year prospective data from the paediatric osteoporosis preventive (POP) study

BACKGROUND

Walking and cycling to school are one source of regular physical activity. The aim of this two years observational study in pre-pubertal children was to evaluate if walking and cycling to school was associated with higher total amount of physical activity and larger gain in bone mineral content (BMC) and bone width than when going by car or bus.

METHODS

133 boys and 99 girls aged 7-9 years were recruited to the Malmö Prospective Paediatric Osteoporosis Prevention (POP) study. BMC (g) was measured by dual X-ray absorptiometry (DXA) in total body, lumbar spine (L2-L4) and femoral neck (FN) at baseline and after 24 months. Bone width was measured in L2-L4 and FN. Skeletal changes in the 57 boys and 48 girls who consistently walked or cycled to school were compared with the 24 boys and 17 girls who consistently went by bus or car. All children remained in Tanner stage I. Level of everyday physical activity was estimated by accelerometers worn for four consecutive days and questionnaires. Comparisons were made by independent student's t-tests between means and Fisher's exact tests. Analysis of covariance (ANCOVA) was used to adjust for group differences in age at baseline, duration of organized physical activity, annual changes in length and BMC or bone width if there were differences in these traits at baseline.

RESULTS

After the adjustments, there were no differences in the annual changes in BMC or bone width when comparing girls or boys who walked or cycled to school with those who went by car or bus. Furthermore, there were no differences in the levels of everyday physical activity objectively measured by accelerometers and all children reached above the by the United Kingdom Expert Consensus Group recommended level of 60 minutes moderate to vigorous physical activity per day.

CONCLUSION

A physical active transportation to school for two years is in pre-pubertal children not associated with a higher accrual of BMC or bone width than a passive mode of transportation, possibly due to the fact that the everyday physical activity in these pre-pubertal children, independent of the mode of school transportation, was high.

Role of physical activity in the prevention of falls and their consequences in the elderly

This work aims to provide an inventory of the risk factors and consequences of falling in the elderly, namely fractures, and to identify strategies to prevent falls and minimise their effects. Falls in elderly people are a major cause of injuries, leading to a general fear of falling, poorer quality of life and even death. The increase in life expectancy brought by developments in the medical and health sciences has not always brought enhanced quality of life. More elderly people live with reduced functional capacities resulting in a higher prevalence of falls and associated problems for themselves and for society. Risk factors for falling, commonly resulting from normal aging processes, have already been identified through multiple studies. Exercise may play an important role in fall prevention and their consequences. Although, effective strategies are usually multi-disciplinary and focus simultaneously on several risk factors. However, only large-scale prevention programmes can have significant effective social impact. To minimise occurrence and consequences of falls, policies to systematically implement prevention programmes should be established.

Effects of an osteoporosis educational programme for men

AIM

This paper reports an evaluation of the effects on knowledge, health beliefs and preventive behaviours of an osteoporosis educational programme for men.

BACKGROUND

Osteoporosis is an increasing global health concern, and educational programmes have been identified as a crucial strategy in its prevention. However, the effectiveness of osteoporosis educational programmes has mainly been evaluated in women.

METHODS

A randomized controlled trial was carried out to identify the effects of an osteoporosis educational programme for men. The study was conducted between September 2004 to February 2005, and 128 Hong Kong Chinese men were randomly assigned to an intervention or control group, with 64 in each group. The intervention group attended an osteoporosis educational programme. All participants completed pre- and post-test self-administered questionnaires: Osteoporosis Knowledge Test, Osteoporosis Health Belief Scale and Osteoporosis Self-Efficacy Scale.

RESULTS

The intervention group showed a statistically significant increase in both knowledge (P < 0.0005) and health beliefs (P = 0.007) about osteoporosis and preventive behaviours in comparison with the control group. However, the difference in self-efficacy between the two groups was not statistically significant (P = 0.154).

CONCLUSIONS

An osteoporosis educational programme can increase men's knowledge levels and change their health beliefs about osteoporosis and preventive behaviours. This approach should be more widely used in nursing practice to promoting the adoption of osteoporosis prevention behaviours in men.

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.

Bone mineral density in Norwegian premenopausal women

The aims of this study were: 1) to determine bone mineral density (BMD) in different age groups, 2) to determine the prevalence of low BMD, and 3) to determine the possible association between BMD and a number of risk factors in Norwegian premenopausal women. BMD of the lumbar spine (L(2)-L(4)), total body, and the hip (total femur, femur neck, and trochanter) were measured using dual-energy X-ray absorptiometry (Prodigy, Lunar) in 145 randomly selected women aged 13-39 years. Information on other factors thought to influence BMD was obtained through questionnaire and a clinical interview. The group aged 25-29 years had the highest mean BMD in the total body, lumbar spine, and total femur while the group aged 13-19 years had the highest mean BMD in the femur neck and the trochanter. The mean BMD values of Norwegian premenopausal women were 3.4-5.1% higher than US/European reference data (P<0.05). Five percent of the study sample aged 20-39 years were defined with low BMD (Z-score <-2) using the standard values from this study. Weight-bearing physical activity, body weight, body height, and age were positively associated with BMD, whilst menstrual dysfunction and previous pregnancy were associated with lower BMD in some of the measurement sites. The results show that the factors associated with BMD are extensive, and the strategies to prevent low BMD have to be multifactorial. A follow-up study should be conducted on the study sample to investigate actual mean BMD values and BMD changes through time.

Dynamic loads are determinants of peak bone mass

This study investigated the association between non-invasive measurements of bone mass and markers of dynamic and static hip joint loads in subjects expected to be at peak bone mass. The bone mineral density (BMD) and bone mineral content (BMC) of three proximal femoral sites (neck, greater trochanter, and total) were measured by dual energy X-ray absorptiometry, and the peak external joint moments at the hip during walking and jogging were calculated from gait analyses of 31 normal human subjects ranging in age from 30 to 49 years (18 females, 13 males). Various multiple regression analyses were performed to determine how much of the variance in BMD and BMC was explained by height, body mass, and the peak hip joint moments. In total, the models explained up to 40% of the variance in BMD and 58% of the variance in BMC. Inclusion of height or body mass did not increase the explanatory power of the models for BMD and explained no more than 8% of the total variance in BMC once the joint moments from walking were allowed to enter the models. These data support the hypothesis that variance in peak bone mass is associated with variance in dynamic hip loads largely independent of the effect of static factors such as height and body mass.

Effect of 8-month vertical whole body vibration on bone, muscle performance, and body balance: a randomized controlled study

Recent animal studies have given evidence that vibration loading may be an efficient and safe way to improve mass and mechanical competence of bone, thus providing great potential for preventing and treating osteoporosis. Randomized controlled trials on the safety and efficacy of the vibration on human skeleton are, however, lacking. This randomized controlled intervention trial was designed to assess the effects of an 8-month whole body vibration intervention on bone, muscular performance, and body balance in young and healthy adults. Fifty-six volunteers (21 men and 35 women; age, 19-38 years) were randomly assigned to the vibration group or control group. The vibration intervention consisted of an 8-month whole body vibration (4 min/day, 3-5 times per week). During the 4-minute vibration program, the platform oscillated in an ascending order from 25 to 45 Hz, corresponding to estimated maximum vertical accelerations from 2 g to 8 g. Mass, structure, and estimated strength of bone at the distal tibia and tibial shaft were assessed by peripheral quantitative computed tomography (pQCT) at baseline and at 8 months. Bone mineral content was measured at the lumbar spine, femoral neck, trochanter, calcaneus, and distal radius using DXA at baseline and after the 8-month intervention. Serum markers of bone turnover were determined at baseline and 3, 6, and 8 months. Five performance tests (vertical jump, isometric extension strength of the lower extremities, grip strength, shuttle run, and postural sway) were performed at baseline and after the 8-month intervention. The 8-month vibration intervention succeeded well and was safe to perform but had no effect on mass, structure, or estimated strength of bone at any skeletal site. Serum markers of bone turnover did not change during the vibration intervention. However, at 8 months, a 7.8% net benefit in the vertical jump height was observed in the vibration group (95% CI, 2.8-13.1%; p = 0.003). On the other performance and balance tests, the vibration intervention had no effect. In conclusion, the studied whole body vibration program had no effect on bones of young, healthy adults, but instead, increased vertical jump height. Future human studies are needed before clinical recommendations for vibration exercise.

Critical periods in human growth and their relationship to diseases of aging

It has long been recognized that there are "critical periods" during mammalian development when exposure to specific environmental stimuli are required in order to elicit the normal development of particular anatomical structures or their normal functioning. The responses of the organism to these stimuli depend on a specific level of anatomical maturation and a state of rapid anatomical and/or functional change. This discussion of critical periods in growth is not confined to the classic definition of a narrow time frame of development during which a particular environmental threshold or limit must exist for normal growth and function to ensue. Using both auxological and epidemiological approaches, we suggest a lifespan perspective which encompasses accumulating and interacting risks that are manifest from prenatal life onward. By understanding the process of growth development, and by scrutinizing the growth process, early variations that lead to later disease can be identified. Here we review a significant amount of the evidence that links exposure during growth to later morbidity and mortality. The fetus appears to respond to insults during the prenatal period through the process of "programming," which has short-term survival advantages but may have a long-term disadvantage in that it is associated with cardiovascular disease, hypertension, type II diabetes, and later obesity. Low birth weight combined with rapid postnatal growth during infancy also appears to be associated, for instance, with later childhood and adult sequelae in terms of glucose tolerance and obesity. Independent of birth weight, the timing of adiposity rebound during mid-childhood also predicts later obesity. The timing, magnitude, and duration of adolescent growth and maturationare associated with critical body composition changes, including the normal acquisition of body fat and bone mineralization. In particular, the acquisition of appropriate peak bone mass is critical in determining the later risk of osteoporosis. A putative causal mechanism linking early growth variation to later chronic disease risk through telomeric attrition is discussed. The obligatory loss of telomeric DNA with each cell division serves as a mitotic clock and marks the rate of growth and repair processes in the cell. Although much more work is required, existing studies support the notion that telomere shortening is not only a clock of cellular division, but also marks relative growth rate, as well as contributing to common degenerative processes of aging through its impact on cellular senescence.

Cbfa1-independent decrease in osteoblast proliferation, osteopenia, and persistent embryonic eye vascularization in mice deficient in Lrp5, a Wnt coreceptor

The low-density lipoprotein receptor-related protein (Lrp)-5 functions as a Wnt coreceptor. Here we show that mice with a targeted disruption of Lrp5 develop a low bone mass phenotype. In vivo and in vitro analyses indicate that this phenotype becomes evident postnatally, and demonstrate that it is secondary to decreased osteoblast proliferation and function in a Cbfa1-independent manner. Lrp5 is expressed in osteoblasts and is required for optimal Wnt signaling in osteoblasts. In addition, Lrp5-deficient mice display persistent embryonic eye vascularization due to a failure of macrophage-induced endothelial cell apoptosis. These results implicate Wnt proteins in the postnatal control of vascular regression and bone formation, two functions affected in many diseases. Moreover, these features recapitulate human osteoporosis-pseudoglioma syndrome, caused by LRP5 inactivation.

Growth rate rather than gender determines the size of the adaptive response of the growing skeleton to mechanical strain

To determine whether male and female skeletons are equally responsive to mechanical load, the left ulnae in a group of juvenile male (n = 7), and age-matched female (n = 9) rats received a short daily period of controlled dynamic loading in vivo (1200 cycles at 2 Hz each day for 10 days) in addition to their normal exercise. Axial loads for each group were adjusted to engender a peak dynamic strain of -4000 microstrain at the medial face of the ulna midshaft, applied and released at a rate of +/-30,000 microstrain/sec. Fluorescent labels were administered at the start and finish of the loading period. Over the course of daily loading, the body mass of the male rats increased 2.5 times faster than that of the females (6.3 g/day vs. 2.5 g/day). The increase in periosteal interlabel bone area due to growth and normal exercise was also 2.5 times greater in the males than in the females. Both genders showed statistically significant (p < 0.05) increases in periosteal new bone deposition in the ulna of their loaded compared with their control limb. The pattern of osteogenic response was similar in males and females and featured increased mineral apposition rate on the lateral surface of the ulna, and arrest of modeling-drift-related resorption with its reversal to bone formation on the medial surface. In males, the absolute loading-related increase in bone area was six times greater than that in females. However, when the absolute size of the loading-related change in periosteal interlabel new bone deposition was expressed relative to that due to growth, there was no difference between males and females (Mean +/- SEM: 37 +/- 12% for males, 34 +/- 12% for females). These data confirm that the ulna of young actively growing rats of both genders responds to a short daily period of loading with an altered modeling response that involves increased bone formation and decreased resorption. Although the absolute amount of new bone formation stimulated by loading is greater in males than in females there is no difference between genders following correction for the higher rate of bone deposition seen in the males in association with their faster rate of growth.

Glucocorticoid excess during adolescence leads to a major persistent deficit in bone mass and an increase in central body fat

Endogenous Cushing's syndrome (CS) in children causes growth retardation, decreased bone mass, and increased total body fat. No prospective controlled studies have been performed in children to determine the long-term sequelae of CS on peak bone mass and body composition. A 15-year-old girl with Cushing disease (CD), and her healthy identical co-twin, were followed for 6 years after the CD was cured. At the 6-year follow-up both twins had areal bone mineral density (BMD) and body composition determined by dual-energy X-ray absorptiometry (DXA) and three-dimensional quantitative computed tomography (3DQCT). Z scores for height, weight, and body mass index (BMI) were -2.3, -0.8 and 0.2, and 1.2, 0.2, and -0.6, in the twin with CD and her co-twin, respectively. In the twin with CD, areal BMD and bone mineral apparent density (BMAD) at different sites varied from 0.7 to 3 SD below her co-twin. Volumetric lumbar spine bone density Z score was -0.75 and 1.0, and total body, abdominal visceral, and subcutaneous fat (%) was 42, 10, and 41 versus 26, 4, and 17 in the twin with CD and her co-twin, respectively. The relationship between total body fat and L2-L4 BMAD was inverse in the twin with CD (p < 0.05), which by contrast in her co-twin was opposite and direct (p < 0.001). In the twin with CD, despite cure, there was a persistent deficit in bone mass and increase in total and visceral body fat. These observations suggest that hypercortisolism (exogenous or endogenous) during adolescence may have persistent adverse effects on bone and fat mass.

Bone mineral density and markers of bone turnover in young adult survivors of childhood lymphoblastic leukaemia

OBJECTIVE

In order to determine if a serious disease like childhood acute lymphoblastic leukaemia (ALL) and the treatment necessary to cure the patients has long term effects on bone mass, we assessed bone mineral density (BMD) and several parameters involved in bone formation in a group of young adult survivors of ALL.

DESIGN AND PATIENTS

Fourteen male and ten female survivors, treated for ALL in childhood, were cross-sectionally studied, at a mean age of 25.1 years (range 20.1-34.9). All patients, except for two, had received cranial irradiation as part of their treatment (mean radiation dose 2460 cGy).

MEASUREMENTS

Height and weight were measured. Bone mineral density (BMD) was assessed using dual energy X-ray absorptiometry in the lumbar spine, femoral neck, femoral trochanter and at 1/3 distal and ultradistal in the radius. Early morning serum levels of LH, FSH, oestradiol or testosterone, IGF-1 and IGF-BP3 were determined as well as several specific markers of bone turnover.

RESULTS

Mean height, expressed as standard deviation score (SDS) was -1.12, significantly reduced. BMD in the lumbar spine, femoral neck and at 1/3 distal and ultradistal in the radius, was significantly lower compared to the reference population (P < 0.05). No correlation was found between the BMD values and the cumulative dose of administered cytotoxic drugs, the age at diagnosis of ALL or the duration of follow-up. Mean IGF-1 and IGF-BP3 SDS-scores were -1.24 and -0.78 respectively, significantly reduced. GH stimulation tests performed in a subgroup of 9 patients showed an insufficient peak GH response in at least one test in all tested patients. The values of LH, FSH oestradiol or testosterone were within the normal adult range. Serum markers of bone formation and bone resorption were in the normal range, indicating that bone turnover was normal at the time of the study.

CONCLUSIONS

Bone development in patients cured of acute lymphoblastic leukaemia is disturbed, resulting in a significantly reduced bone mineral density. Impaired growth hormone activity, as a long term effect of cranial irradiation, may be one of the underlying causes as well as the illness itself and the administered cytotoxic drugs. Since a reduced bone mineral density predispose patients to osteoporosis, intervention in order to improve bone mass should be considered.

Relationship between bone mineral density of the proximal femur and strength of hip muscles in postmenopausal women

The relationship between muscle strength and bone density is well known, but only a limited number of studies relating muscle strength to bone mineral density of a site-specific limb have been performed. The main purposes of this study were as follows: (1) to assess the relationship between the strength of hip muscles and bone mineral density of the proximal femur in 100 postmenopausal women; (2) to compare strength values of three subgroups, which were formed on the basis of the femoral neck Z-scores. By using an isokinetic dynamometer (Cybex 350), muscle strength tests were performed for hip muscles and bone mineral density measurements were obtained by dual energy x-ray absorptiometry. Statistical analysis demonstrated a moderately positive correlation between bone mineral density of the femoral neck and hip muscle strength (with abductors: r = 0.267, P = 0.008; with adductors: r = 0.276, P = 0.007). A moderate correlation was also found between bone mineral density of Ward's triangle and hip adductors (r = 0.327; P = 0.001). When muscle strength mean values of subgroups were compared with each other, there was no statistically significant differences. These data may suggest that the isokinetic strength of hip muscles may not contribute to the bone mineral density of the proximal femur.

Randomized controlled study of effects of sudden impact loading on rat femur

Physical loading creating high peak strains on the skeleton at high strain rates is suggested to be the most effective type of activity in terms of bone mineral acquisition. This study assessed the effects of sudden impact loading on mineral and mechanical bone properties in 13-week-old Sprague-Dawley rats. The rats were randomly assigned as sedentary controls (SED, n = 10), control animals receiving low-intensity exercise (EX, n = 15), and experimental animals receiving low-intensity exercise combined with sudden impact-loading (EX + IMP, n = 15). In the EX group, the rats walked in a walking mill at a speed of 10 cm/s for 20 minutes/day, 5 days/week for 9 weeks. In the EX + IMP group, the program was identical to the EX group except for the additional sudden impacts administered to their skeleton during the walking exercise. At the start, there were 50 impacts per session, after which their number was gradually increased to 200 impacts per session by week 6 and then kept constant until the end of the experiment, week 9. These horizontally and vertically directed body impacts were produced by a custom-made walking mill equipped with computer-controlled high-pressure air cylinders. After sacrifice, both femora of each rat were removed and their dimensions, bone mineral content (BMC) by dual-energy X-ray absorptiometry, and mechanical properties by femoral shaft three-point bending and femoral neck compression were determined. The cortical wall thickness increased significantly in the EX and EX + IMP groups as compared with SEDs (+7.6%, p = 0.049 and +10%, p = 0.020, respectively). The EX + IMP group showed +9.0% (p = 0.046) higher cross-sectional moment of inertia values than the EX group. No significant intergroup differences were seen in the BMC values, while the breaking load of the femoral shaft (EX + IMP vs. SED +8.8%,p = 0.047) and femoral neck (EX + IMP vs. SED +14.1%, p = 0.013) was significantly enhanced by the impact loading. In conclusion, this study indicates that mechanical loading can substantially improve the mechanical characteristics of a rat femur without simultaneous gain in its mineral mass. If this is true in humans too, our finding gives an interesting perspective to the numerous longitudinal exercise studies (of women) in which the exercise-induced gains in bone mass and density have remained mild to moderate only.

Development of mass, density, and estimated mechanical characteristics of bones in Caucasian females

Three hundred and thirty healthy Finnish girls and premenopausal women, aged 7-47 years, were examined to evaluate the natural development of bone mineral mass and density from early childhood to menopause. Bone mineral content (BMC,g) and areal density (BMD, g/cm2) were measured from the spine (L2-L4), femoral neck, trochanter region of the femur, and distal radius using dual-energy X-ray absorptiometry (DXA). In addition, the bone mineral apparent density (BMAD, g/cm3) was assessed from the above described skeletal sites, and the mechanical competence of the femoral neck was estimated. Special attention was paid to the timing of the peak values of these bone parameters as well as to the evidence of premenopausal bone loss. The BMC, BMD, and BMAD of the spine, femoral neck, and trochanter region of the femur achieved peak values around the age of 20, and the bone loss seemed to start soon thereafter. In contrast, the bone mass of the distal radius slightly increased between the ages of 20 and 47. In the femoral neck, the estimated bending strength achieved its peak value around the age of 20 and showed a slight decrease during the following decades. The highest body weight and neck-length adjusted strength values of the femoral neck were, however, found in early childhood, with the values decreasing linearly thereafter. In conclusion, this study supports previous findings of rapid bone mineral accumulation in late adolescence, and occurrence of the peak bone mass and density around the age of 20. Premenopausal bone loss seems to occur in the proximal femur and lumbar spine. Our observations of femur strength development imply that from childhood to menopause the mechanical strength of the femoral neck is well adjusted to the biomechanical loading requirements of the body.

The effect of calcium supplementation and Tanner stage on bone density, content and area in teenage women

One hundred and twelve Caucasian girls, 11.9 +/- 0.5 years of age at entry, were randomized into a 24-month, double-masked, placebo-controlled trial to determine the effect of calcium supplementation on bone mineral content, bone area and bone density. Supplementation was 500 mg calcium as calcium citrate malate (CCM) per day. Controls received placebo pills, and compliance of both groups averaged 72%. Bone mineral content, bone mineral area and bone mineral density of the lumbar spine and total body were measured by dual energy X-ray absorptiometry (DXA). Calcium intake from dietary sources averaged 983 mg/day for the entire study group. The supplemented group received, on average, an additional 360 mg calcium/day from CCM. At baseline and after 24 months, the two groups did not differ with respect to anthropometric measurements, urinary reproductive hormone levels or any measurement of pubertal progression. The supplemented group had greater increases of total body bone measures: content 39.9% versus 35.7% (p = 0.01), area 24.2% versus 22.5% (p = 0.15) and density 12.2% versus 10.1% (p = 0.005). Region-of-interest analyses showed that the supplemented group had greater gains compared with the control group for bone mineral density, content and area. In particular, in the lumbar spine and pelvis, the gains made by the supplemented group were 12%-24% greater than the increases made by the control group. Bone acquisition rates in the two study groups were further compared by subdividing the groups into those with below- or above-median values for Tanner score and dietary calcium intake. In subjects with below-median Tanner scores, bone acquisition was not affected by calcium supplementation or dietary calcium level. However, the calcium supplemented subjects with above-median Tanner had higher bone acquisition rates than the placebo group with above-median Tanner scores. Relative to the placebo group, the supplemented group had increased yearly gains of bone content, area and density which represented about 1.5% of adult female values. Such increases, if held to adult skeletal maturity, could provide protection against future risk of osteoporotic fractures.