Lifestyle risk factors for osteoporosis in Asian and Caucasian girls

Bone Strength in Girls and Boys After a Distal Radius Fracture: A 2-Year HR-pQCT Double Cohort Study

We recently reported impaired bone strength in girls with low- to moderate-energy distal radius fractures (Fx) compared with girls with no history of forearm fractures (Non-Fx). We aimed to determine whether bone strength deficits observed at baseline were still present after 2 years. We assessed bone strength, microarchitecture, and bone mineral density (BMD) of the non-fractured (Fx) and non-dominant (Non-Fx) distal radius (7% site) at baseline, 12, and 24 months using high-resolution pQCT (Scanco Medical, Brüttisellen, Switzerland) in 104 girls (aged 11.0 ± 1.7 years; 47 Fx, 57 Non-Fx) and 157 boys (aged 12.7 ± 1.7 years; 86 Fx, 71 Non-Fx). Bone outcomes included total area (Tt.Ar) and bone mineral density (Tt.BMD), trabecular bone volume ratio (BV/TV), thickness (Tb.Th), separation (Tb.Sp), and number (Tb.N), and cortical BMD (Ct.BMD), thickness (Ct.Th), and porosity (Ct.Po). We used finite element analysis to estimate bone strength (failure load [F.Load]; ultimate stress [U.Stress]; load-to-strength ratio). We used sex-specific mixed-effects models to compare bone outcomes between Fx and Non-Fx over 2 years. In girls, those with fractures had 18% to 24% lower U.Stress and 5% to 9% lower Tt.BMD than Non-Fx at all time points (p < 0.017). In secondary analysis by fracture degree, girls with low-energy (LE) fractures had 19% to 21% lower F.Load, 25% to 47% lower U.Stress, 11% to 14% lower Tt.BMD, and 11% to 15% lower BV/TV than Non-Fx at all time points (p < 0.017). In contrast, boys' bone outcomes were similar between Fx and Non-Fx at all time points. In secondary analysis by fracture degree, boys with LE fractures had 10% lower Tt.BMD and 10% lower Ct.Th compared with Non-Fx at 12 months only. Deficits in distal radius bone strength and trabecular bone microarchitecture appear to track across 2 years after a forearm fracture in girls but not in boys. Longer follow-up is needed to determine whether deficits persist into adulthood in women and how they may influence future risk of fragility fracture. © 2017 American Society for Bone and Mineral Research.

A comparison of bone quality at the distal radius between Asian and white adolescents and young adults: an HR-pQCT study

Paradoxically, Asians have lower areal bone mineral density (aBMD), but their rates of hip and wrist fractures are lower than whites. Therefore, we used high-resolution pQCT (HR-pQCT) to determine whether differences in bone macrostructure and microstructure, BMD, and bone strength at the distal radius were apparent in Asian (n = 91, 53 males, 38 females, [mean ± SD] 17.3 ± 1.5 years) and white (n = 89, 46 males, 43 females, 18.1 ± 1.8 years) adolescents and young adults. HR-pQCT outcomes included total BMD (Tt.BMD), trabecular bone volume fraction (BV/TV), and trabecular number (Tb.N), thickness (Tb.Th), and separation (Tb.Sp). We used an automated segmentation algorithm to determine total bone area (Tt.Ar), and cortical BMD (Ct.BMD), porosity (Ct.Po), and thickness (Ct.Th), and we applied finite element (FE) analysis to HR-pQCT scans to estimate bone strength. We fit sex-specific multivariable regression models to compare bone outcomes between Asians and whites, adjusting for age, age at menarche (girls), lean mass, ulnar length, dietary calcium intake, and physical activity. In males, after adjusting for covariates, Asians had 11% greater Tt.BMD, 8% greater Ct.BMD, and 25% lower Ct.Po than whites (p < 0.05). Also, Asians had 9% smaller Tt.Ar and 27% greater Ct.Th (p < 0.01). In females, Asians had smaller Tt.Ar than whites (16%, p < 0.001), but this difference was not significant after adjusting for covariates. Asian females had 5% greater Ct.BMD, 12% greater Ct.Th, and 11% lower Tb.Sp than whites after adjusting for covariates (p < 0.05). Estimated bone strength did not differ between Asian and white males or females. Our study supports the notion of compensatory elements of bone structure that sustain bone strength; smaller bones as observed between those of Asian origin compared with white origin have, on average, more dense, less porous, and thicker cortices. Longitudinal studies are needed to determine whether ethnic differences in bone structure exist in childhood, persist into old age, and whether they influence fracture risk.

Cortical porosity is higher in boys compared with girls at the distal radius and distal tibia during pubertal growth: an HR-pQCT study

The aim of this study was to determine the sex- and maturity-related differences in bone microstructure and estimated bone strength at the distal radius and distal tibia in children and adolescents. We used high-resolution pQCT to measure standard morphological parameters in addition to cortical porosity (Ct.Po) and estimated bone strength by finite element analysis. Participants ranged in age from 9 to 22 years (n = 212 girls and n = 186 boys) who were scanned annually for either one (11%) or two (89%) years at the radius and for one (15%), two (39%), or three (46%) years at the tibia. Participants were grouped by the method of Tanner into prepubertal, early pubertal, peripubertal, and postpubertal groups. At the radius, peri- and postpubertal girls had higher cortical density (Ct.BMD; 9.4% and 7.4%, respectively) and lower Ct.Po (-118% and -56%, respectively) compared with peri- and postpubertal boys (all p < 0.001). Peri- and postpubertal boys had higher trabecular bone volume ratios (p < 0.001) and larger cortical cross-sectional areas (p < 0.05, p < 0.001) when compared with girls. Based upon the load-to-strength ratio (failure load/estimated fall force), boys had lower risk of fracture than girls at every stage except during early puberty. Trends at the tibia were similar to the radius with differences between boys and girls in Ct.Po (p < 0.01) and failure load (p < 0.01) at early puberty. Across pubertal groups, within sex, the most mature girls and boys had higher Ct.BMD and lower Ct.Po than their less mature peers (prepuberty) at both the radius and tibia. Girls in early, peri-, and postpubertal groups and boys in peri- and postpubertal groups had higher estimates of bone strength compared with their same-sex prepubertal peers (p < 0.001). These results provide insight into the sex- and maturity-related differences in bone microstructure and estimated bone strength.

Site specificity of bone architecture between the distal radius and distal tibia in children and adolescents: An HR-pQCT study

High-resolution quantitative computerized tomography permits evaluation of site specific differences in bone architecture. The purpose of this study was to compare bone architecture between distal radius and distal tibia. We present bone architecture at the distal radius and distal tibia in 151 male and 172 female participants, as follows: total bone area (mm(2)), total bone density (mg HA/cm(3)), trabecular bone density (mg HA/cm(3)), cortical bone density (mg HA/cm(3)), cortical thickness (μm), trabecular number (1/mm), trabecular thickness (μm), and trabecular separation (μm). We evaluated differences in and correlations between bone variables (absolute values) across sites. We calculated individual z scores and used regression to assess discordance between sites. In pubertal and postpubertal male and female participants, absolute values of total bone area, cortical bone density, cortical thickness, and trabecular thickness were significantly lower at the radius compared with the tibia (P < 0.01). Absolute values for trabecular bone density were significantly lower at the radius compared with the tibia in postpubertal male and female participants (P < 0.01). Absolute values for trabecular separation was significantly lower at the radius compared with the tibia in pubertal female participants (P < 0.01). Bone architecture was moderately to highly correlated between sites (r = 0.34-0.85). There was discordance between z scores at the radius and tibia within male participants (pubertal R (2) between 36 and 64%; postpubertal R (2) between 22 and 77%) and female participants (pubertal R (2) between 10 and 44%; postpubertal R (2) between 25 and 62%). In conclusion, it is vital to evaluate bone architecture at the specific skeletal site of interest.

Does a novel school-based physical activity model benefit femoral neck bone strength in pre- and early pubertal children?

The effects of physical activity on bone strength acquisition during growth are not well understood. In our cluster randomized trial, we found that participation in a novel school-based physical activity program enhanced bone strength acquisition and bone mass accrual by 2-5% at the femoral neck in girls; however, these benefits depended on teacher compliance with intervention delivery. Our intervention also enhanced bone mass accrual by 2-4% at the lumbar spine and total body in boys.

INTRODUCTION

We investigated the effects of a novel school-based physical activity program on femoral neck (FN) bone strength and mass in children aged 9-11 yrs.

METHODS

We used hip structure analysis to compare 16-month changes in FN bone strength, geometry and bone mineral content (BMC) between 293 children who participated in Action Schools! BC (AS! BC) and 117 controls. We assessed proximal femur (PF), lumbar spine (LS) and total body (TB) BMC using DXA. We compared change in bone outcomes between groups using linear regression accounting for the random school effect and select covariates.

RESULTS

Change in FN strength (section modulus, Z), cross-sectional area (CSA), subperiosteal width and BMC was similar between control and intervention boys, but intervention boys had greater gains in BMC at the LS (+2.7%, p = 0.05) and TB (+1.7%, p = 0.03) than controls. For girls, change in FN-Z tended to be greater (+3.5%, p = 0.1) for intervention girls than controls. The difference in change increased to 5.4% (p = 0.05) in a per-protocol analysis that included girls whose teachers reported 80% compliance.

CONCLUSION

AS! BC benefits bone strength and mass in school-aged children; however, our findings highlight the importance of accounting for teacher compliance in classroom-based physical activity interventions.

The bare bones of race

In this paper I examine claims of racial difference in bone density and find that the use and definitions of race in medicine lack a theoretical foundation. My central argument is that the social produces the biological in a system of constant feedback between body and social experience. By providing a different angle of vision on claimed racial differences I hope to move the conversation away from an ultimately futile discussion of nature versus nurture, where time is held constant and place seen as irrelevant, and begin to build a new paradigm for examining the contributions of geographic ancestry, individual lifecycle experience, race, and gender to varied patterns of health and disease.

Bone mineral and predictors of bone mass in white, Hispanic, and Asian early pubertal girls

Differences in bone among racial/ethnic groups may be explained by differences in body size and shape. Previous studies have not completely explained differences among white, Asian, and Hispanic groups during growth. To determine racial/ethnic differences and predictors of bone mass in early pubertal girls, we measured bone mineral content (BMC) in white, Hispanic, and Asian sixth-grade girls across six states in the United States. We developed models for predicting BMC for the total-body, distal radius, total-hip, and lumbar spine for 748 subjects. For each of the bone sites, the corresponding area from dual-energy X-ray absorptiometry (DXA) was a strong predictor of BMC, with correlations ranging 0.78-0.98, confirming that larger subjects have more BMC. Anthropometric measures of bone area were nearly as effective as bone area from DXA at predicting BMC. For total-body, distal radius, lumbar spine, and total-hip BMC, racial/ethnic differences were explained by differences in bone area, sexual maturity, physical activity, and dairy calcium intake. Bone size explained most of the racial/ethnic differences in BMC, although behavioral indicators were also significant predictors of BMC.

Bone mineral density in female high school athletes: interactions of menstrual function and type of mechanical loading

During adolescence, skeletal integrity of girls is largely dependent on menstrual function and impact exercise, yet currently there is limited research regarding the interaction between menstrual status and type of mechanical loading associated with various high school sports. Our purpose was to examine associations of menstrual status, type of mechanical loading, and bone mineral density (BMD) in female high school athletes participating in high/odd impact or repetitive/non-impact sport. Participants were 161 female high school athletes (15.7+/-1.3 years; 165.3+/-6.9 cm; 59.4+/-8.7 kg) representing high/odd impact (n=93, including soccer, softball, volleyball, tennis, lacrosse, and track sprinters and jumpers), or repetitive/non-impact sports (n=68, including swimmers, cross-country and track distance runners who participated in events>or=800 m). Areal BMD was measured by DXA at the spine (L1-L4), proximal femur, and total body. Menstrual status was determined by self-report. Athletes with primary, secondary or oligomenorrhea were combined into a single group (oligo/amenorrheic) and compared to eumenorrheic athletes. Analysis of covariance (ANCOVA) with Bonferroni post hoc comparisons adjusted for age, BMI, and gynecological age were used to compare BMD of athletes in combined mechanical loading and menstrual status groups. We found significantly greater total hip (p=0.04) and trochanter (p=0.02) BMD (g cm(-2)) among eumenorrheic high/odd impact compared to eumenorrheic repetitive/non-impact athletes, and greater spine (p=0.01) and trochanter (p=0.04) BMD among high/odd impact eumenorrheic athletes compared to repetitive/non-impact oligo/amenorrheic athletes. Chi-squared analysis of BMD Z-scores adjusted for gynecological age showed a significantly greater percentage of repetitive/non-impact athletes (33.9%) compared to high/odd impact athletes (11.8%) with low spine BMD for their age (BMD Z-score<or=-1 SD) (p=0.001), indicating that a high percentage of female high school athletes participating in repetitive loading sports, and especially those with oligo/amenorrhea, may not be accruing bone at the expected rate. Female adolescent athletes should be evaluated periodically and advised of the possible negative effects of oligo/amenorrhea on bone health.

Prevalence and etiology of low bone mineral density in juvenile systemic lupus erythematosus

OBJECTIVE

Studies of adults with systemic lupus erythematosus (SLE) have frequently demonstrated the presence of decreased bone mineral density (BMD). However, there have been few investigations in pediatric patients to date. This study was undertaken to determine the prevalence of low BMD in patients with juvenile SLE and to identify associated risk factors.

METHODS

We studied 64 consecutive patients with juvenile SLE in whom routine dual x-ray absorptiometry (DXA) scanning was performed. Lumbar spine osteopenia was defined as a BMD Z score of < -1 and > or = -2.5, and osteoporosis as a BMD Z score of < -2.5. Decreased hip BMD was defined as a value of < 80%. Data on disease activity, quality of life, disease-related damage, sex, ethnicity, body mass index, age at diagnosis, age at DXA, medication use and duration, clinical features, and puberty status were collected at the time of DXA.

RESULTS

Lumbar spine osteopenia was seen in 24 patients (37.5%) and osteoporosis in 13 (20.3%). Decreased hip BMD was present in 12 patients (18.8%). By univariate analysis, osteopenia was significantly correlated with age, disease duration, duration of corticosteroid use, cumulative corticosteroid dose, azathioprine use, cyclophosphamide use, lupus nephritis, and damage. Two additional variables, mycophenolate mofetil use and class III-IV nephritis, were associated with osteoporosis. Abnormal hip BMD was associated with disease duration, duration of corticosteroid use, and cumulative corticosteroid dose. By multivariate analysis, only disease duration remained in the model for osteoporosis and abnormal hip BMD, while cumulative corticosteroid dose was the variable associated with osteopenia.

CONCLUSION

These results indicate that osteopenia and osteoporosis are common in juvenile SLE and are associated more closely with increased disease duration than with cumulative corticosteroid dose.

Bone strength and its determinants in pre- and early pubertal boys and girls

Higher fracture rates in women than men may be related to a sex difference in bone strength that is thought to emerge during growth. However, sexual dimorphism in bone strength and the determinants of bone strength in boys and girls are not well understood. Thus, our objectives were to (1) compare tibial bone strength and its components (geometry and density) between pre- and early pubertal boys and girls and (2) identify the contribution of muscle cross-sectional area and other modulating factors to bone outcomes. We used pQCT to assess the distal tibia (8%) and tibial midshaft (50%) in 424 Asian and Caucasian pre- and early pubertal boys and girls. Our primary outcomes were bone strength index (BSI, mg2/mm(4)) at the distal tibia and strength strain index (SSI, mm3) at the midshaft. We also assessed components of bone strength including bone geometry [total (ToA) and cortical (CoA) cross-sectional areas, mm2] and total (ToD, mg/cm3) and cortical (CoD, mg/cm3) density. We used ANCOVA to compare bone outcomes between boys and girls in each maturity group (PRE or EARLY pubertal by Tanner stage) and multiple regression to evaluate the contribution of muscle cross-sectional area (MCSA, mm2 by pQCT), maturity, ethnicity, physical activity, dietary calcium, and vertical jump height to bone outcomes. After adjusting for tibial length and MCSA, bone strength indices were 6-15% (P < 0.05) greater in PRE and EARLY boys compared with PRE and EARLY girls. The sex difference in bone strength was due largely to greater bone areas (4-6%) in boys. At the distal tibia ToD was significantly greater in PRE boys (6%, P < 0.001) compared with PRE girls and at the midshaft CoD was slightly greater in both PRE and EARLY girls (1%, P = 0.01). After adjusting for tibial length, MCSA was the primary explanatory variable of tibial bone geometry and strength in both sexes accounting for 10-16% of the variance. The influence of maturity, ethnicity, physical activity, and dietary calcium on pQCT bone outcomes was small and was both site- and sex-specific. Sexual dimorphism in tibial bone strength is evident in prepuberty. Our results are consistent with a functional model of bone development in which bone adapts its geometry and strength to withstand challenges from muscle forces during growth.

Predicting physical activity intention and behaviour among children in a longitudinal sample

We examined predictors of leisure-time physical activity intention and behaviour in children, and the potential direct and moderating effects of gender and ethnicity. Participants were 364 (230 Asian; 134 Caucasian) 9-11-year-old children who completed measures of the theory of planned behaviour (TPB) and physical activity behaviour (Physical Activity Questionnaire for Children) across three, 3-month intervals (i.e., two prediction time-periods) in Canada. The TPB explained 35-50% of the variance in physical activity behaviour and 74-76% of the variance in intention using structural equation modelling. An autoregressive longitudinal path model showed that the TPB predicted changes in physical activity and physical activity predicted changes in TPB constructs (p<.05). Overall, intention and perceived behavioural control were significant (p<.05) contributors to the direct prediction of behaviour and subjective norm and perceived behavioural control were significant (p<.05) predictors of intention. Gender did not show a robust relationship with physical activity or intention, but the effect of ethnicity on physical activity was mediated through perceived behavioural control (Asians less active than Caucasians). Finally, gender and ethnicity did not moderate TPB and physical activity relations (p<.05). These data suggest that childhood may be a formative stage for the development of physical activity cognitions and that promoting physical activity in children may require normative and control-based intervention.

Calcium supplementation for improving bone mineral density in children

BACKGROUND

Clinical trials have shown that calcium supplementation in children can increase bone mineral density (BMD) although this effect may not be maintained. There has been no quantitative systematic review of this intervention.

OBJECTIVES

. To determine the effectiveness of calcium supplementation for improving BMD in children. . To determine if any effect varies by sex, pubertal stage, ethnicity or level of physical activity, and if any effect persists after supplementation is ceased.

SEARCH STRATEGY

We searched CENTRAL, (Cochrane Central Register of Controlled Trials) (Issue 3, 2005), MEDLINE (1966 to 1 April 2005), EMBASE (1980 to 1 April 2005), CINAHL (1982 to 1 April 2005), AMED (1985 to 1 April 2005), MANTIS (1880 to 1 April 2005) ISI Web of Science (1945 to 1 April 2005), Food Science and Technology Abstracts (1969 to 1 April 2005) and Human Nutrition (1982 to 1 April 2005). Conference abstract books (Osteoporosis International, Journal of Bone and Mineral Research) were hand-searched.

SELECTION CRITERIA

Randomised controlled trials of calcium supplementation (including by food sources) compared with placebo, with a treatment period of at least 3 months in children without co-existent medical conditions affecting bone metabolism. Outcomes had to include areal or volumetric BMD, bone mineral content (BMC), or in the case of studies using quantitative ultrasound, broadband ultrasound attenuation and ultrasonic speed of sound, measured after at least 6 months of follow-up.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data including adverse events. We contacted study authors for additional information.

MAIN RESULTS

The 19 trials included 2859 participants, of which 1367 were randomised to supplementation and 1426 to placebo. There was no heterogeneity in the results of the main effects analyses to suggest that the studies were not comparable. There was no effect of calcium supplementation on femoral neck or lumbar spine BMD. There was a small effect on total body BMC (standardised mean difference (SMD) +0.14, 95% CI+0.01, +0.27) and upper limb BMD (SMD +0.14, 95%CI +0.04, +0.24). Only the effect in the upper limb persisted after supplementation ceased (SMD+0.14, 95%CI+0.01, +0.28). This effect is approximately equivalent to a 1.7% greater increase in supplemented groups, which at best would reduce absolute fracture risk in children by 0.1-0.2%per annum. There was no evidence of effect modification by baseline calcium intake, sex, ethnicity, physical activity or pubertal stage. Adverse events were reported infrequently and were minor.

AUTHORS' CONCLUSIONS

While there is a small effect of calcium supplementation in the upper limb, the increase in BMD which results is unlikely to result in a clinically significant decrease in fracture risk. The results do not support the use of calcium supplementation in healthy children as a public health intervention. These results cannot be extrapolated to children with medical conditions affecting bone metabolism.

Efeitos da atividade física na densidade mineral óssea e na remodelação do tecido ósseo

Este artigo revisa os efeitos de diferentes modalidades esportivas e do treinamento de força na remodelação óssea e discutir as possíveis relações da densidade mineral óssea (DMO) com a força muscular e a composição corporal. Numerosos estudos indicam que a atividade física de alto impacto, ou que exija alta produção de força, pode ter um efeito benéfico na DMO, devido à deformação desse tecido, ocorrida durante a atividade. Alguns autores têm avaliado os efeitos do treinamento físico em alguns marcadores bioquímicos da remodelação óssea, já que a variação das concentrações desses marcadores pode indicar um estado de formação ou reabsorção óssea. Entretanto, a inconsistência dos resultados encontrados sugere que a análise dos efeitos da atividade física na remodelação óssea, através desses marcadores, deve ser mais investigada. Existem muitas discrepâncias a respeito da relação entre a DMO com a força muscular e a composição corporal, principalmente na determinação de qual desses fatores está mais associado com a DMO. A determinação de qual o tipo de atividade física seja ideal para aumentar o pico de massa óssea na adolescência, ou mesmo mantê-la após a idade adulta, é muito importante para a prevenção e o possível tratamento da osteoporose.

Osteoporosis health beliefs and practices among Korean immigrants in Nova Scotia

The purpose of this research was to investigate osteoporosis knowledge, as well as health beliefs and practices among Korean immigrants in Nova Scotia. Twenty-six participants (18 women and eight men) completed the questionnaire. The mean age of participants was 48, and their average length of stay in Canada was 14 years. The mean osteoporosis knowledge score was 50% for both men and women and perceived susceptibility to the disease was low, especially in men. Perceived seriousness and health motivation was high relative to perceived susceptibility. Only 62% indicated both that their diet met their nutritional and cultural needs, and changes in dietary and exercise habits since arrival in Canada were reported by 73 and 64%, respectively. This study helped identify existing osteoporosis awareness weaknesses in this population: a). Perceived susceptibility, especially for men; and b). knowledge related to prevention and treatment options, including diet and exercise.

Ultrasound bone measurements in pre-adolescent girls: interaction between ethnicity and lifestyle factors

AIM

We obtained calcaneal ultrasound measurements in 198 girls between 7.5 and 11.7 y of age, representing ethnic groups (black [n = 80], white [n = 41], mixed ancestral origin [n = 77]) in South Africa.

METHODS

Anthropometry was assessed. Demographics, physical activity, habitual dietary calcium intake and pubertal development were quantified by questionnaires. Broadband ultrasound attenuation (BUA) and speed of sound (SOS) of the left calcaneus were measured. Girls in Tanner breast stage 5 and/or those menstruating were excluded from analysis.

RESULTS

Black girls were lighter than white girls (31.4 +/- 7.8 vs 34.8 +/- 7.5 kg; p < 0.05), and shorter than girls of mixed ancestral origin (1.29 +/- 0.08 vs 1.34 +/- 0.07 m; p < 0.001) and white girls (1.35 +/- 0.07 m; p < 0.001), after adjusting for age. Reported calcium intake scores were higher in black than white girls (21.6 +/- 11.1 vs 16.1 +/- 8.4; p < 0.01). Total peak bone strain score (TPBSS) was higher in white compared to black girls (6.8 +/- 4.8 vs 5.0 +/- 4.7; p < 0.05), while walking energy expenditure (MET h/wk) was higher in black girls compared to the other groups (p < 0.001). BUA and SOS were higher in the black girls (59.6 +/- 13.7 dB/MHz; 1575.1 +/- 22.6 m/s; p < 0.001) and girls of mixed ancestral origin (59.0 +/- 12.5 dB/MHz; 1567.8 +/- 26.1 m/s; p < 0.01) than in the white girls (50.4 +/- 8.7 dB/MHz; 1552.1 +/- 19.5 m/s). Co-varying for age and weight did not affect these results. Walking energy expenditure (r = 0.20) and calcium score (r = 0.17) were correlated (p < 0.05) with SOS for the whole group.

CONCLUSION

Ultrasound parameters were lower in the white compared to the black girls, who consumed more calcium on average, but who were lighter, shorter and performed less impact activity. This suggests that interactions between ethnicity and lifestyle factors determine bone quality in premenarcheal girls.

Bone mass and structure are enhanced following a 2-year randomized controlled trial of exercise in prepubertal boys

Exercise during growth has a positive influence on bone mineral accrual, yet little is known about how bone geometry and strength adapt to loading during growth. Our primary objective was to compare changes in proximal femur bone geometry and strength between 31 prepubertal (Tanner Stage 1) boys who participated in a school-based, high-impact circuit intervention (12 min, three times a week) for 20 months and 33 maturity-matched controls. Our secondary objective was to compare changes in total body (TB), proximal femur (PF), and lumbar spine (LS) bone mineral content (BMC) and bone area (BA) in these groups. We assessed geometric variables and bone strength at the narrow neck (NN), intertrochanteric (TR) region, and femoral shaft regions by applying the Hip Structure Analysis program to proximal femur dual energy X-ray absorptiometry scans (DXA, Hologic QDR 4500). Further, we assessed total body, lumbar spine, and proximal femur BMC and BA by DXA and derived total body lean mass and fat mass from total body scans. Intervention (10.2 +/- 0.5 years) and control boys (10.1 +/- 0.5 years) had similar baseline height (140.8 vs. 141.3 cm) and weight (36.9 vs. 35.4 kg), and average 20-month physical activity scores (Physical Activity Questionnaire for Children, PAQ-C) and calcium intakes (861 vs. 852 mg/day, food frequency questionnaire). Twenty-month height and weight changes were not significantly different between groups; lean mass changed more (P < 0.05) in intervention boys (22.8%) than control boys (18.6%). At the NN region, intervention boys had greater bone expansion on both the periosteal (+2.6%, P = 0.1) and endosteal (+2.7%, P = 0.2) surfaces, resulting in significantly greater changes in section modulus (bone bending strength) (+7.5%, P = 0.02, ANCOVA, adjusting for height change, final Tanner Stage, and baseline bone values). Changes at the intertrochanteric and femoral shaft regions were not significantly different between groups. Femoral neck (FN) BMC changes were significantly greater in intervention boys (+4.3%, P < 0.01); changes in BA and BMC for other regions were not significantly different between groups. In summary, a school-based, high-impact exercise intervention implemented three times a week for 12 min is an effective strategy for site-specific gains in bone strength at the narrow neck region of the proximal femur.

A school-based exercise intervention elicits substantial bone health benefits: a 2-year randomized controlled trial in girls

OBJECTIVE

Childhood weight-bearing physical activity is recognized as an important determinant of peak bone mass, and physical activity intervention may represent a feasible strategy for primary prevention of osteoporosis. Previous school-based exercise interventions have all been of <10 months in duration. We implemented a high-impact, circuit-based, jumping intervention (10 minutes, 3 times a week) over 2 school years and compared changes in bone mineral content (BMC) over 20 months (2 school years) in 9.9 +/- 0.6-year-old intervention girls (N = 32) and controls (10.3 +/- 0.4 years, N = 43).

METHODS

We measured BMC for the total body, lumbar spine, proximal femur (and femoral neck and trochanteric subregions), and lean and fat mass by dual-energy radiograph absorptiometry (Hologic QDR 4500), and height, sitting height, leg length, and weight at baseline and 20 months. We assessed Tanner stage, general physical activity, and calcium intake by questionnaire.

RESULTS

Girls were Tanner breast stage 1 to 3 at baseline. There were no significant differences in baseline or 20-month change in body size or composition, average physical activity, or calcium intake between groups. There were substantially greater gains in lumbar spine (41.7% vs 38.0%) and femoral neck (24.8% vs 20.2%) BMC in intervention than in control girls (P <.05, analysis of covariance; covariates were baseline BMC and height, change in height, physical activity, and final Tanner stage).

CONCLUSION

Three brief sessions of high-impact exercise per week implemented over 2 consecutive years within the elementary school curriculum elicited a substantial bone mineral accrual advantage in pubertal girls.

Is there a critical period for bone response to weight-bearing exercise in children and adolescents? a systematic review

This systematic review examines and compares the bone mineral changes in children and adolescents, as measured by dual energy x ray absorptiometry, reported in exercise intervention studies. The effects of hormonal factors and growth on bone mineral change during puberty are examined, and the possibility of a critical period during which bone is especially adaptable to exercise is discussed.

Prepubertal Asians have less limb skeletal muscle

Skeletal muscle mass in prepubertal Asian children has not been examined previously. The aims of this study were to test the hypotheses that 1) prepubertal Asians have less appendicular skeletal muscle (ASM) mass compared with African-Americans and Caucasians, and 2) ASM is less in prepubertal Asian girls compared with Asian boys. ASM was estimated by using dual-energy X-ray absorptiometry in healthy prepubertal girls (n = 170) and boys (n = 166). The results showed that, after adjusting for age, height, and body weight, 1) Asian girls and boys had less amounts of ASM than African-Americans (P < 0.001); 2) Asian girls had less amounts of ASM than Caucasian girls (P = 0.004); 3) there was a trend towards less ASM in Asian compared with Caucasian boys (P = 0.07); 4) and Asian girls had significantly less ASM than Asian boys (P < 0.001). This study indicates that skeletal muscle mass as a fraction of body weight is smaller in Asian compared with African-American and Caucasian children.

Bone mineral response to a 7-month randomized controlled, school-based jumping intervention in 121 prepubertal boys: associations with ethnicity and body mass index

We examined the effects of a 7-month jumping intervention (10 minutes, 3 times per week) on bone mineral gain in prepubertal Asian and white boys (10.3+/-0.6 years, 36.0+/-9.2 kg) at 14 schools randomized to control (n = 60) and intervention (n = 61) groups. Intervention and control groups had similar mean baseline and change in height, weight, lean mass and fat mass, baseline areal bone mineral density (aBMD; g/cm2), bone mineral content (BMC; g; dual-energy X-ray absorptiometry [DXA], QDR 4500W), and similar average physical activity and calcium intakes. Over 7 months, the intervention group gained more total body (TB) BMC (1.6%,p < 0.01) and proximal femur (PF) aBMD (1%, p < 0.05) than the control group after adjusting for age, baseline weight, change in height, and loaded physical activity. We also investigated the 41 Asian and 50 white boys (10.2+/-0.6 years and 31.9+/-4.4 kg) who were below the 75th percentile (19.4 kg/m2) of the cohort mean for baseline body mass index (BMI). Boys in the intervention group gained significantly more TB and lumbar spine (LS) BMC, PF aBMD, and trochanteric (TR) aBMD (+ approximately2%) than boys in the control group (adjusted for baseline weight, final Tanner stage, change in height, and loaded physical activity). Bone changes were similar between Asians and whites. Finally, we compared the boys in the control group (n = 16) and the boys in the intervention group (n = 14) whose baseline BMI fell in the highest quartile (10.5+/-0.6 years and 49.1+/-8.2 kg). Seven-month bone changes (adjusted as aforementioned) were similar in the control and intervention groups. In summary, jumping exercise augmented bone mineral accrual at several regions equally in prepubertal Asian and white boys of average or low BMI, and intervention effects on bone mineral were undetectable in high BMI prepubertal boys.