Associations between physical activity and bone mass in black and white South African children at age 9 yr

Osteoporosis in Africa-where are we now

Africa is experiencing an exponential increase in the number of older persons. The number of persons surviving with human immunodeficiency virus is simultaneously increasing due to improved availability of anti-retroviral therapy. The burden of non-communicable diseases, in particular, osteoporosis and its consequent fragility fractures, is also predicted to increase. Osteoporosis, however, remains a neglected disease and there are no age-standardized reference data available to accurately screen and diagnose individuals with osteoporosis. Epidemiological studies reporting the incidence of hip fracture or vertebral fractures are limited from Africa, especially Sub-Saharan Africa. The studies are usually limited as they are based on a retrospective data and small study numbers and often from a single study site. However, compared with early initial studies, the more recent studies show that osteoporosis and fractures are increasing across the continent. The overall incidence rates for osteoporosis and fractures still vary greatly between different regions in Africa and ethnic groups. Predisposing factors are similar with those in developed countries, but awareness of osteoporosis is sorely lacking. There is a lack of awareness among the population as well as health authorities, making it extremely difficult to quantify the burden of disease. There is great potential for research into the need and availability of preventive strategies. The FRAX® tool needs to be developed for African populations and may circumvent the shortage of bone densitometry.

Skeletal loading score is associated with bone microarchitecture in young adults

Physical activity that involves high strain magnitudes and high rates of loading is reported to be most effective in eliciting an osteogenic bone response. Whether a history of participation in osteogenic activities during youth, as well as current participation in osteogenic activities, contributes to young adult bone microarchitecture and strength is unknown.

PURPOSE

We determined the association between a new skeletal loading (SkL) score reflecting physical activity from age 11 to adulthood, the bone specific physical activity questionnaire (BPAQ) and bone microarchitecture in young Black and White men and women.

METHODS

We conducted a cross-sectional study of young ([mean ± SD] 23.7 ± 3.3 years) Black (n = 51 women, n = 31 men) and White (n = 50 women, n = 49 men) adults. Microarchitecture and estimated bone strength (by micro-finite element analysis) were assessed at the ultradistal tibia using high-resolution peripheral quantitative computed tomography (HR-pQCT). Physical activity questionnaires were administered and a SkL score was derived based on ground reaction force, rate of loading, frequency, duration, and life period of participation per activity from age 11 onwards. BPAQ score was also calculated. We used multiple linear regression to determine associations between both SkL score and BPAQ score and bone outcomes, adjusting for age, height, weight, sex, and race.

RESULTS

We found that SkL score, which accounts for current and historical physical activity, was significantly associated with most cortical bone parameters at the tibia including area, area fraction, porosity, thickness, and tissue mineral density (R² = 0.27-0.55, all p < 0.01). Further, trabecular thickness, separation, number, and bone mineral density (R² = 0.22-0.32, all p < 0.01), as well as stiffness and failure load (R² = 0.63-0.65, all p < 0.01), were associated with the SkL score. The BPAQ was also significantly associated with most bone parameters, but to a lesser degree than SkL score.

CONCLUSION

These findings suggest that among young adults, greater amounts of osteogenic physical activity, as assessed by the SkL score and BPAQ are associated with improved bone microarchitecture and strength. With the potential to predict bone parameters in young adults, these scores may ultimately serve to identify those most vulnerable to fracture.

Organized Sport Participation From Childhood to Adolescence Is Associated With Bone Mass in Young Adults From the Raine Study

There is a critical need for longitudinal cohort studies to consider the association of the cumulative exposure of physical activity during childhood and adolescence and bone mass. The aim of this study was to investigate the relationship between organized sports trajectories (that capture distinct and potentially meaningful patterns over critical developmental periods) and bone mass at age 20 years. Participation in organized sport was recorded by parental report at ages 5, 8, 10, 14, and 17 years in 984 offspring (48% female) of a pregnancy cohort (Raine Study). Latent class analysis identified three trajectory classes in each sex. In females, these were "consistent sport participators" (48%), "dropouts" (34%), and "non-participators" (18%); in males, "consistent sport participators" (55%), "dropouts" (37%), and "sport joiners" (8%). Whole-body bone mineral content (BMC) at age 20 years was assessed by dual-energy X-ray absorptiometry (DXA). At age 20 years, after adjustment for covariates measured at age 20 years, including height, lean mass, physical activity, calcium intake, serum 25-hydroxyvitamin D, alcohol, and smoking, males who were "consistent sport participators" had significantly greater whole-body and leg BMC than those who dropped out of sport (p < 0.001), whereas males who joined sports had significantly greater leg BMC than those who dropped out of sport (p = 0.002). Females in the "consistent sport participator" trajectory had significantly greater leg BMC than those who dropped out (all p = 0.004). Participation in organized sport during childhood and adolescence is associated with bone mass at age 20 years. Because attainment of optimal peak bone mass in young adulthood is protective against osteoporosis in later life, this may have long-term skeletal benefits. © 2018 American Society for Bone and Mineral Research.

The effect of loading and ethnicity on annual changes in cortical bone of the radius and tibia in pre-pubertal children

BACKGROUND

It is unclear what effect habitual physical activity or ethnicity has on annual changes in bone size and strength in pre-pubertal children.

AIM

To determine whether the annual relative change in bone size and strength differed between high and low bone loaders and also between black and white pre-pubertal children.

SUBJECTS AND METHODS

Peripheral quantitative computed tomography (pQCT) scans of the 65% radius and tibia were completed on 41 black and white children (15 boys, 26 girls) between the ages of 8-11 years, at baseline and 1 year later. Children were categorised into either a high or low bone loading group from a peak bone strain score obtained from a bone-specific physical activity questionnaire. Total area (ToA), cortical area (CoA), cortical density (CoD), strength-strain index (SSI), periosteal circumference (PC), endosteal circumference (EC) and cortical thickness (CT) were assessed.

RESULTS

There was no difference in annual relative change in radial or tibia bone size and strength between the low and high bone loaders. Black children had a greater annual relative change in CoD (p = 0.03) and SSI (p = 0.05) compared to the white children.

CONCLUSION

Children who performed high bone loading activities over a 1-year period had similar bone growth to children who did low bone loading activities over the same period. Rapid maturational growth over this period may have resulted in bone adapting to the strains of habitual physical activity placed on it. Black children may have greater tibial bone strength compared to white children due to a greater annual increase in cortical density.

Decreased Vigorous Physical Activity in School-Aged Children with Human Immunodeficiency Virus in Johannesburg, South Africa

OBJECTIVE

To describe physical activity in South African children with and without HIV.

STUDY DESIGN

Study measurements were obtained in 218 children with perinatal HIV and 180 children without HIV aged 5-9 years in a study conducted in Johannesburg, South Africa. Weight-for-age z-score, height-for-age z-score, frequency and duration of moderate and vigorous physical activity, and sedentary behaviors were obtained. These measurements were compared between children with and without HIV.

RESULTS

Weight-for-age z-score and height-for-age z-score were significantly lower for children with HIV compared with those without HIV. Among children who attended school, fewer children with HIV than children without HIV participated in physical education (41% vs 64%; P = .0003) and organized after-school sports (38% vs 64%; P < .001). The proportion of children in both groups meeting World Health Organization recommendations for physical activity was similar (84% overall); however, girls with HIV spent less time in vigorous physical activity than girls without HIV (420 vs 780 minutes/week; P = .001). This difference remained significant even when girls with a medical condition with the potential to limit physical activity were excluded, and after adjusting for age. Time spent in sedentary behaviors did not differ significantly between the two groups.

CONCLUSION

Although children with HIV with well-controlled disease after initiating antiretroviral therapy early in life achieve high levels of physical activity, vigorous physical activity is lower in girls with HIV than in healthy controls. This finding may reflect lower participation in school-based physical education and organized after-school physical activity.

Patterns and Associated Factors of Physical Activity among Adolescents in Nigeria

INTRODUCTION

Understanding the context where adolescents' physical activity (PA) takes place could impact a more targeted approach to implement PA promotion and interventions in Africa. However, standardized data on adolescents' PA behaviour is lacking in Nigeria. We described PA patterns in the various domains (home, school, transport, leisure-time) and intensity categories (light-intensity PA, moderate- to vigorous- intensity physical activity [MVPA] and total PA), and their associations with sociodemographic factors and socioeconomic status (SES) among secondary school adolescents in Nigeria.

METHODS

A cross-sectional survey was conducted in a representative sample of 1006 secondary school adolescents (12-18 years, 50.4% girls) in Maiduguri, Nigeria. Self-reported PA was assessed with an adapted version of the Activity Questionnaire for Adolescents and Young Adults. Outcomes were weekly minutes (min/wk) of PA spent in the various domains and intensity categories. Multivariate ANOVA was used to examine associations of PA scores (domains and intensity levels) with adolescents' sociodemographic characteristics and SES, and track differences in PA scores between subgroups.

RESULTS

The total sample reported most PA at school (1525 min/wk), the least during active transportation (210 min/wk), and only 37% engaged in 60 min of MVPA daily. Boys reported significantly more leisure-time PA (P<0.001), active transportation (P<0.001), MVPA (P = 0.023) and total PA (P = 0.003) than girls, while girls reported more school-based PA (P = 0.009), home-based PA (P<0.001) and light-intensity PA (P<0.001) than boys. Moderate-intensity PA (P = 0.024) and total PA (P = 0.049) were significantly higher in younger age group than in older group. Household car ownership was associated with less active transportation (P = 0.009), less moderate-intensity PA (P = 0.048) and with more leisure-time PA (P = 0.013). High parental SES was associated with more leisure-time PA (P = 0.002), more MVPA (P = 0.047) and less active transportation (P<0.001). Adolescents of various weight status differed significantly in their leisure-time PA (P<0.001), moderate-intensity PA (P = 0.011) and total PA (P = 0.033).

CONCLUSIONS

The patterns and levels of physical activity among adolescents in Nigeria vary according to the adolescents' age, gender, weight status and SES. These findings have important public health implications for identifying subgroups of Nigerian adolescents that should be targeted for effective physical activity promoting interventions.

Nutrient patterns and their association with socio-demographic, lifestyle factors and obesity risk in rural South African adolescents

The aim of this study was to identify and describe the diversity of nutrient patterns and how they associate with socio-demographic and lifestyle factors including body mass index in rural black South African adolescents. Nutrient patterns were identified from quantified food frequency questionnaires (QFFQ) in 388 rural South African adolescents between the ages of 11-15 years from the Agincourt Health and Socio-demographic Surveillance System (AHDSS). Principle Component Analysis (PCA) was applied to 25 nutrients derived from QFFQs. Multiple linear regression and partial R2 models were fitted and computed respectively for each of the retained principal component (PC) scores on socio-demographic and lifestyle characteristics including body mass index (BMI) for age Z scores. Four nutrient patterns explaining 79% of the total variance were identified: PCI (26%) was characterized by animal derived nutrients; PC2 (21%) by vitamins, fibre and vegetable oil nutrients; PC3 (19%) by both animal and plant derived nutrients (mixed diet driven nutrients); and PC4 (13%) by starch and folate. A positive and significant association was observed with BMI for age Z scores per 1 standard deviation (SD) increase in PC1 (0.13 (0.02; 0.24); p = 0.02) and PC4 (0.10 (-0.01; 0.21); p = 0.05) scores only. We confirmed variability in nutrient patterns that were significantly associated with various lifestyle factors including obesity.

Bone density in black and white South African women: contribution of ethnicity, body weight and lifestyle

Ethnic differences in bone mineral density (BMD) between healthy adult black and white South African women were studied. Higher BMD was only noted at the femoral sites in black women. Body weight significantly impacted these findings. A lower fracture risk at all skeletal sites cannot be assumed in black South African (SA) women.

PURPOSE

Bone mineral density (BMD) varies amongst women of different ethnicities. African-Americans have higher BMD at all skeletal sites compared with whites. On the African continent, bone density studies suggest site-specific ethnic differences in BMD. To examine the contribution of body weight and lifestyle characteristics to ethnic differences in BMD between adult black and white South African women, we assessed lumbar spine (SBMD), femoral neck (FNBMD) and total femoral BMD (FTBMD) by dual-energy X-ray absorptiometry (DXA) in 184 black and 143 white women aged between 23 and 82 years.

METHODS

BMDs were compared amongst pre- and postmenopausal blacks and whites before and after adjustment for covariates with significant univariate association with BMD. Volumetric bone mineral apparent density (BMAD) of the spine and femoral neck was also calculated to account for ethnic differences in bone size.

RESULTS

Before adjustment, SBMD was lower (p < 0.05), FTBMD similar and FNBMD (p < 0.01) higher in premenopausal black women. Similar SBMD, but significantly higher BMD at the femoral sites (p < 0.01), was noted in postmenopausal blacks compared with whites. Amongst anthropometric measures and lifestyle factors, only adjustment for weight significantly altered these observed ethnic differences in bone density. After adjustment for weight, SBMD remained lower in premenopausal blacks and became lower in young postmenopausal blacks. Weight adjustment eliminated all ethnic differences in proximal femoral BMD measurements, with the exception of FNBMD that remained higher in younger postmenopausal blacks. Before adjustment, calculated SBMAD was similar and FNBMAD consistently higher in blacks in all the menstrual groups. Adjustment for weight did not alter these findings.

CONCLUSION

Most of the observed ethnic difference in BMD was explained by differences in body weight between black and white SA women. The higher femoral BMD in older blacks may explain, the lower hip fracture prevalence in black South African women. The lower SBMD in pre- and postmenopausal black women in this study suggests that factors other than BMD should be considered to explain a lower vertebral fracture prevalence in blacks, if a lower fracture prevalence does indeed exist.

Physical activity throughout adolescence and bone mineral density in early adulthood: the 1993 Pelotas (Brazil) Birth Cohort Study

Association between three physical activity (PA) measurements throughout adolescence and bone density at 18 years of age was investigated. PA was associated with both lumbar spine and femoral neck bone mineral density (BMD) in early adulthood independent of type of PA used in the analysis. The results were more consistent in boys.

INTRODUCTION

This study amis to evaluate if PA during adolescence could influence BMD later in life.

METHODS

A population-based birth cohort study was carried out. PA was assessed at 11 and 15 years of age by questionnaire and included sports performed while BMD (lumbar spine and femoral neck) was measured by dual-energy X-ray absorptiometry at 18 years. A peak strain score was generated based on ground reaction forces of different PA. PA was measured as peak strain score, peak strain score multiplied by minutes/week and minutes/week. Unadjusted and adjusted analyses were performed using linear regression.

RESULTS

Overall, 3,811 adolescents were studied (1,866 boys and 1,945 girls). The peak strain score at 11 and 15 years was associated with lumbar and femoral neck BMD at 18 years in boys. Among girls, high-impact PA at 11 years was positively associated with lumbar and femoral BMD (p = 0.01; p < 0.001). After adjusted analysis, weekly minutes of PA at 11 years were not associated with lumbar spine but were associated with femoral neck BMD (p < 0.001); at 15 years, weekly minutes of PA were positively associated with BMD at both sites. Regardless of PA status at 11 years of age, attaining the recommendations of PA (300 min/week) at 15 years appears to be important for BMD at 18 years in both sites in boys and girls. The results Appeared to be more consistent in boys.

CONCLUSIONS

PA during adolescence was positively associated with both lumbar spine and femoral neck BMD in early adulthood independent of type of PA used in the analysis.

Evidence of an overweight/obesity transition among school-aged children and youth in Sub-Saharan Africa: a systematic review

BACKGROUND

Prevalence of childhood overweight/obesity has increased considerably in recent years. The transition to higher rates of overweight/obesity has been well documented in high income countries; however, consistent or representative data from lower income countries is scarce. It is therefore pertinent to assess if rates of overweight/obesity are also increasing in lower income countries, to inform public health efforts.

OBJECTIVE

This systematic review aimed to investigate the evidence for an overweight/obesity transition occurring in school-aged children and youth in Sub Saharan Africa.

METHODS

Studies were identified by searching the MEDLINE, Embase, Africa Index Medicus, Global Health, Geobase, and EPPI-Centre electronic databases. Studies that used subjective or objective metrics to assess body composition in apparently healthy or population-based samples of children and youth aged 5 to 17 years were included.

RESULTS

A total of 283 articles met the inclusion criteria, and of these, 68 were used for quantitative synthesis. The four regions (West, Central, East, and South) of Sub Saharan Africa were well represented, though only 11 (3.9%) studies were nationally representative. Quantitative synthesis revealed a trend towards increasing proportions of overweight/obesity over time in school-aged children in this region, as well as a persistent problem of underweight. Weighted averages of overweight/obesity and obesity for the entire time period captured were 10.6% and 2.5% respectively. Body composition measures were found to be higher in girls than boys, and higher in urban living and higher socioeconomic status children compared to rural populations or those of lower socioeconomic status.

CONCLUSIONS

This review provides evidence for an overweight/obesity transition in school-aged children in Sub Saharan Africa. The findings of this review serve to describe the region with respect to the growing concern of childhood overweight/obesity, highlight research gaps, and inform interventions.

PROSPERO REGISTRATION NUMBER

CRD42013004399.

Temporal trends and correlates of physical activity, sedentary behaviour, and physical fitness among school-aged children in Sub-Saharan Africa: a systematic review

Recent physical activity (PA) and fitness transitions, identified as behavioural shifts from traditionally active lifestyles to more industralised and sedentary lifestyles, have been observed among school-aged children. There is a wealth of supporting evidence of such behavioural transitions in high income countries; however, a paucity of data on lower income countries exists. These transitions pose a particular threat to the welfare of children by accelerating the onset of chronic diseases. This systematic review investigated the evidence for a PA and fitness transition among Sub-Saharan Africa's school-aged children. Temporal trends and correlates of PA, SB, and fitness were examined. Studies were identified by searching the Medline, Embase, Africa Index Medicus, Global Health, Geobase, and EPPI-Centre electronic databases, and were included if they measured outcomes of interest in apparently healthy samples of children (5‒17 years). A total of 71 articles met the inclusion criteria (40 informed PA, 17 informed SB, and 37 informed fitness). Vast heterogeneity in study methodology complicated analysis of transitions over time and no temporal trends were immediately discernible. However, higher socioeconomic status, urban living, and female children were found to engage in lower levels of PA, higher SB, and performed worse on aerobic fitness measures compared to lower socioeconomic status, rural living, and male children. Data revealed that urbanization was associated with a trend towards decreased PA, increased SB, and decreased aerobic fitness over time. Representative, temporally sequenced data examining a PA and fitness transition are lacking in this region (PROSPERO Registration Number: CRD42013004399).

Physical activity and sedentary behavior among adolescents in rural South Africa: levels, patterns and correlates

BACKGROUND

Physical inactivity is increasing among children and adolescents and may be contributing to the increasing prevalence of overweight and obesity. This study examines physical activity and sedentary behavior patterns, and explores associations with individual, maternal, household, and community factors amongst rural South African adolescents.

METHODS

In 2009, 381 subjects, stratified by ages 11-12-years and 14-15-years, were randomly selected from 3511 children and adolescents who had participated in a growth survey two years previously. Weight and height were measured and self-reported Tanner pubertal stage was collected. A questionnaire quantifying frequency and duration of physical activity (PA) domains and sedentary time for the previous 12 months was administered. Moderate-vigorous physical activity (MVPA mins/wk) was calculated for time spent in school and club sport. Socio-demographic and other related data were included from the Agincourt health and socio-demographic system (HDSS). The Agincourt HDSS was established in 1992 and collects prospective data on the community living in the Agincourt sub-district of Mpumalanga Province in rural north-east South Africa.

RESULTS

Puberty, maternal education and socio-economic status (SES) contributed significantly to the mulitiple linear regression model for sedentary behavior (R2 = 0.199; adjusted R2 = 0.139; p < 0.000), and sex, SES and maternal education contributed to the tobit regression model for school and club sport MVPA (p < 0.000). MVPA, calculated from school and club sport, was higher in boys than girls (p < 0.001), and informal activity was lower (boys: p < 0.05 and girls: p < 0.01) while sedentary time was higher (girls: p < 0.01) in the older than the younger groups. Ninety-two percent (92%) of the sample reported walking for transport.

CONCLUSIONS

In this study of rural South African adolescent boys and girls, SES at the maternal, household and community level independently predicted time spent in sedentary behaviors, and school and club MVPA. This study provides local data that can be used to develop health promotion strategies specific to this community, and other similar communities in developing countries.

A two-year history of high bone loading physical activity attenuates ethnic differences in bone strength and geometry in pre-/early pubertal children from a low-middle income country

We examined the interplay between ethnicity and weight-bearing physical activity on the content and volumetric properties of bone in a pre- to early pubertal South African Black and White population. Sixty six children [Black boys, 10.4 (1.4)yrs, n=15; Black girls, 10.1 (1.2)yrs, n=27; White boys, 10.1 (1.1)yrs, n=7; White girls, 9.6 (1.3)yrs, n=17] reported on all their physical activities over the past two years in an interviewer administered physical activity questionnaire (PAQ). All participants underwent a whole body and site-specific DXA scan and we also assessed bone structure and estimated bone strength with pQCT. Children were classified as being either high or low bone loaders based on the cohort's median peak bone strain score estimated from the PAQ. In the low bone loading group, Black children had greater femoral neck bone mineral content (BMC) (2.9 (0.08)g) than White children (2.4 (0.11)g; p=0.05). There were no ethnic differences in the high bone loaders for femoral neck BMC. At the cortical site, the Black low bone loaders had a greater radius area (97.3 (1.3) vs 88.8 (2.6)mm(2); p=0.05) and a greater tibia total area (475.5 (8.7) vs. 397.3 (14.0)mm(2); p=0.001) and strength (1633.7 (60.1) vs. 1271.8 (98.6)mm(3); p=0.04) compared to the White low bone loaders. These measures were not different between the Black low and high bone loaders or between the Black and White high bone loaders. In conclusion, the present study shows that there may be ethnic and physical activity associations in the bone health of Black and White pre-pubertal children and further prospective studies are required to determine the possible ethnic specific response to mechanical loading.

Genetic factors influencing bone mineral content in a black South African population

Bone mass differs according to ethnic classification, with individuals of African ancestry attaining the highest measurements across numerous skeletal sites. Elevated bone mass is even maintained in those individuals exposed to adverse environmental factors, suggesting a prominent genetic effect that may have clinical or therapeutic value. Using a candidate gene approach, we investigated associations of six candidate genes (ESR1, TNFRSF11A, TNFRSF11B, TNFSF11, SOST and SPP1) with bone mass at the hip and lumbar spine amongst pre-pubertal black South African children (mean age 10.6 years) who formed part of the longitudinal Birth to Twenty cohort. 151 black children were genotyped at 366 polymorphic loci, including 112 previously associated and 254 tagging single nucleotide polymorphisms (SNPs). Linear regression was used to highlight significant associations whilst adjusting for height, weight, sex and bone area. Twenty-seven markers (8 previously associated and 19 tag SNPs; P < 0.05) were found to be associated with either femoral neck (18) or lumbar spine (9) bone mineral content. These signals were derived from three genes, namely ESR1 (17), TNFRSF11B (9) and SPP1 (1). One marker (rs2485209) maintained its association with the femoral neck after correction for multiple testing (P = 0.038). When compared to results amongst Caucasian adults, we detected differences with respect to associated skeletal sites. Allele frequencies and linkage disequilibrium patterns were also significantly different between populations. Hence, our results support the existence of a strong genetic effect acting at the femoral neck in black South African children, whilst simultaneously highlighting possible causes that account for inter-ethnic bone mass diversity.

Cortical porosity in children is determined by age-dependent osteonal morphology

INTRODUCTION

Fracture rates in children are high. Cortical bone makes a major contribution to bone strength, determined by cortical geometry, mineralization and porosity. Of these, porosity remains least well explored. Since most cortical canals are part of an osteon, we examined osteons and their canals for age-related changes in numbers, size and shape in 87 iliac crest bone samples of subjects aged 0-25 years, using histomorphometry.

RESULTS

Three types of secondary osteons were identified: drifting, eccentric and concentric. 1. Drifting osteons predominated to the mid-teens, were large, asymmetrical, and had giant canals (remodeling space) with the resorption front drifting towards the marrow. The cause of drift remains unclear. Onset of formation appeared delayed, and commenced on the periosteum-facing surface. From the mid-teens numerical density of drifting osteons decreased, and so did porosity. 2. Eccentric osteons were smaller, more circular and had a small excentric canal; their numerical density gradually increased with age. 3. Concentric osteons (adult bone) were the smallest, most symmetrical osteons, had a small central canal, and markedly increased in numerical density from the mid-teens. Boys showed greater overall porosity and greater numerical density of drifting osteons, and later change to concentric osteons than girls. Whites had greater numerical density and greater areal density of resorption cavities than blacks.

CONCLUSIONS

Structure of osteons and canals varied during growth. Large asymmetrical drifting osteons with giant active canals (remodeling space) predominated until the mid-teens and accounted for > 70% of childhood cortical porosity. Thereafter smaller concentric (adult type) osteons increasingly predominated. Gender differences may relate to greater fracture rates in boys, and race differences to greater fracture rates in whites. The role of osteocyte-mediated mechanotransduction in osteonal structure and cortical porosity during growth warrants further exploration.

Effect of strength training and the practice of Alpine skiing on bone mass density, growth, body composition, and the strength and power of the legs of adolescent skiers

This work examines the influence of practicing strength training and Alpine skiing over 2 years on bone mineral density (BMD), growth, body composition, and the strength and power of the legs of adolescent skiers. The study subjects were 20 adolescent skiers (10 girls and 10 boys) and 19 sedentary adolescents (9 girls and 10 boys), all 13-16 years of age. The BMDs of the lumbar column (L2-L4) and hip (neck of the femur, trochanter, and Ward's triangle) were determined by dual x-ray photon absorptiometry at the beginning and end of the experimental period. The increase in height and the percentage fat and muscular masses of the subjects were also recorded, as was their ability to jump (countermovement jump [CMJ]), their leg strength and power (squat test), and their leg anaerobic power (continuous jump test [CMJ15″]). No significant differences were seen in the increase in height, body weight, or percentage fat mass between the skiers and sedentary subjects, although the boy skiers showed a significant increase in percentage muscular mass (p < 0.05) compared to the sedentary boys. The improvement in the values of the different CMJ variables was significantly greater among the boy skiers than among the sedentary boys (p < 0.001-0.01). The same was true for the girls (p < 0.001), except for CMJ15″. The skiers experienced a significantly greater increase in L2-L4 BMD than the sedentary subjects (boys p < 0.05; girls p < 0.01). These results suggest that Alpine skiing combined with rational strength training involves no special risk for the physical development of young people, has a positive effect on the power and the percentage of muscle mass in the legs, and helps to have a higher bone density in the lumbar spine (L2-L4).

Site-specific differences in bone mineral density in black and white premenopausal South African women

SUMMARY

We examined ethnic differences in bone mineral density (BMD) and the contribution of body composition, lifestyle and socioeconomic factors in South African women. Femoral neck and total hip BMD were higher, but lumbar spine BMD was lower in black women, with body composition, lifestyle and socioeconomic status (SES) factors contributing differently in ethnic groups.

INTRODUCTION

There is a paucity of data on the relative contribution of body composition, lifestyle factors and SES, unique to different ethnic groups in South Africa, to BMD. We examined differences in femoral neck (FN), total hip (TH) and lumbar spine (LS) BMD between black and white premenopausal South African women and the associations between BMD and body composition, lifestyle factors and SES in these two ethnic groups.

METHODS

BMD and body composition were measured in 240 black (27 ± 7; 18-45 years) and 187 white (31 ± 8; 18-45 years) women using dual-energy X-ray absorptiometry. Questionnaires were administered to examine SES, physical activity and dietary intake.

RESULTS

After co-varying for age, FN and TH were higher in black than white women (FN 0.882 ± 0.128 vs. 0.827 ± 0.116 g/cm(2), P < 0.001; TH 0.970 ± 0.130 vs. 0.943 ± 0.124 g/cm(2), P = 0.018). When adjusting for ethnic differences in body composition, LS was higher in white than black women. In black women, fat-free soft tissue mass, SES and injectable contraceptive use explained 33-42% of the variance in BMD at the hip sites and 22% at the LS. In white women, fat-free soft tissue mass and leisure activity explained 24-30% of the variance in BMD at the hip sites, whereas fat mass, leisure activity and oral contraceptive use explained 11% of the variance at the LS.

CONCLUSION

FN and TH BMD were higher, but LS BMD was lower in black than white South African women with body composition, lifestyle and SES factors contributing differently to BMD in these women.

Heterogeneity of fracture pathogenesis in urban South African children: the birth to twenty cohort

South African black children fracture less than white children. Differences in bone mass, body composition, and physical activity may be contributing risk factors. This study aimed to investigate the association between fracture prevalence, bone mass, and physical activity in South African children. Using the Bone Health cohort of the Birth to Twenty longitudinal study, we retrospectively obtained information of lifetime fractures until age 15 years in 533 subjects. Whole-body bone mineral content (BMC), bone area (BA), fat mass (FM), and lean mass (LM) (measured by dual-energy X-ray absorptiometry [DXA]), anthropometric data, physical activity scores, and skeletal maturity were obtained at ages 10 and 15 years. Nonfracturing black females were used as the control group and comparisons were made between those who did and did not fracture within the same sex and ethnic groups. Of the 533 subjects, 130 (24%) reported a fracture (black, 15%; white, 41.5%; p  <  0.001). White males who fractured were significantly taller (10 years, p  <  0.01), more physically active (15 years, p  <  0.05) and had higher LM (10 years, p  =  0.01; 15 years, p  <  0.001), whereas white females who fractured were fatter (10 and 15 years, p  =  0.05 and p  <  0.05, respectively), than their nonfracturing peers. White males who fractured had greater BA and BMC at all sites at 10 and 15 years compared to their nonfracturing peers after adjusting for differences in height and weight; BA and BMC were similar in each of the other sex and ethnic groups. No anthropometric or bone mass differences were found between black children with and without fractures. The factor associated with fractures in white males appears to be participation in sports activities, while in white females obesity appears to play a role. No contributing factors in black males and females were found, and needs further elucidation.

Bone mass and bone size in pre- or early pubertal 10-year-old black and white South African children and their parents

Genetic factors are thought to maintain bone mass in socioeconomically disadvantaged black South Africans. We compared bone mass between environmentally disadvantaged black and advantaged white children and their parents, after determining the most appropriate method by which to correct bone mineral content (BMC) for size. We collected data from 419 healthy black and white children of mean age 10.6 years (range 10.0-10.9), 406 biological mothers, and 100 biological fathers. Whole-body, femoral neck, lumbar spine, and mid- and distal one-third of radius bone area (BA) and BMC were measured by dual-energy X-ray absorptiometry. Power coefficients (PCs) were calculated from the linear-regression analyses of ln(BMC) on ln(BA) and used to correct site-specific BMC for bone size differences. Heritability (½h(2), %) by maternal and paternal descent was estimated by regressing children's Z scores on parents' Z scores. Correcting BMC for height, weight, and BA(PC) accounted for the greatest variance of BMC at all skeletal sites. In so doing, BMC in blacks was up to 2.6 times greater at the femoral neck and lumbar spine. Maternal and paternal heritability was estimated to be ~30% in both black and white subjects. These results may in part explain the lower prevalence of fragility fractures at the hip in black South African children when compared to whites. Heritability was comparable between environmentally disadvantaged black and advantaged white South African children and similar to that reported for Caucasians in other parts of the world.

Determinants of bone size and strength in 13-year-old South African children: the influence of ethnicity, sex and pubertal maturation

We have previously shown ethnic differences in bone mass between pre-pubertal black and white children using DXA. To investigate these ethnic differences further, using pQCT, and to determine the influence of sex and pubertal development, we measured appendicular bone variables in 13-year-old children using pQCT. We collected pQCT data on a cohort of 471 black and white children at age 13years. Black boys and girls were shorter and had less lean mass than their white peers, and black boys were lighter than white boys at an earlier stage of pubertal development. Metaphyseal (4%) radial trabecular density was greater in the black girls than their white peers (239.5±49.5 vs. 222.7±34.2 mg/cm(3); p<0.05). Bone strength index was not different between the ethnic groups. All metaphyseal measures were 3-41% greater in boys than girls, after adjusting for height where appropriate. Diaphyseal (38%) tibial values, including total area, endosteal diameter, tibial diameter, periosteal circumference and polar strength-strain index were 4-22% greater in the black than white children and in boys than in girls. Cortical density was greater in black than white boys (1079.0±39.4 vs. 1058.7±34.5 mg/mm(3); p<0.001) and greater in the girls than boys (black: 1129.3±33.7 vs. 1079.0±39.4 mg/mm(3); p<0.001; white: 1126.8±28.3 vs. 1058.7±34.5mg/mm(3); p<0.001). Cortical thickness was less in the black groups. Lower leg muscle cross-sectional area (MCSA) was higher in white than black children, and forearm MCSA was higher in white than black boys. There was no difference in fat cross-sectional area between the ethnic groups. In conclusion, ethnic and sex differences in both metaphyseal and diaphyseal bone parameters exist during puberty, which are not accounted for by differences in body size or skeletal maturity. South African black children have wider diaphyseal regions of appendicular bones with greater measures of bone strength.

Factors influencing the vitamin D status of 10-year-old urban South African children

OBJECTIVE

Assessment of vitamin D status in a cohort of healthy 10-year-old urban children and the factors that influence vitamin D status in these children.

DESIGN

A cross-sectional study. Blood samples were collected across four seasons of the year for the biochemical determination of serum 25-hydroxyvitamin D [25(OH)D]. Anthropometric measurements (height and weight), BMI and total fat and lean mass (determined by the dual energy X-ray absorptiometry) were measured. 25(OH)D concentrations were assessed by chemiluminescent assay.

SETTING

Study of children in the Greater Johannesburg area of South Africa who form the Bone Health sub-cohort of the longitudinal Birth to Twenty cohort.

SUBJECTS

Three hundred and eighty-five children who form the Bone Health sub-cohort of the longitudinal Birth to Twenty cohort.

RESULTS

White children had significantly higher 25(OH)D than their black peers (120·0 (sd 36·6) nmol/l v. 93·3 (sd 34·0) nmol/l, respectively). Seasonal variations in 25(OH)D levels were found only in white children, with 25(OH)D levels being significantly higher in white than in black children during the autumn and summer months. In multiple regression analysis, season, ethnicity, sex and total fat mass were the factors found to have an influence on 25(OH)D. Vitamin D deficiency (7 %) and insufficiency (19 %) were uncommon among the 10-year-old children.

CONCLUSIONS

Vitamin D supplementation or fortification is not warranted in healthy children living in Johannesburg. However, further studies need to confirm this in other regions of the country, especially in those living further south and with less sunshine during the winter months.

HealthKick: a nutrition and physical activity intervention for primary schools in low-income settings

BACKGROUND

The burden of non-communicable diseases, including type 2 diabetes, is growing in South Africa. This country has a complex mix of over- and under-nutrition, especially in low-income communities, and concerning levels of physical inactivity in children and youth. This paper describes HealthKick, a school-based nutrition and physical activity intervention in primary schools in these settings aimed at reducing diabetes risk factors.

METHODS/DESIGN

This study includes schools within historically disadvantaged, low-income communities from an urban area close to the city of Cape Town and from two rural areas outside of Cape Town, South Africa. The three Educational Districts involved are Metropole North, Cape Winelands and the Overberg. The study has three phases: intervention mapping and formative assessment, intervention development, and outcome and process evaluation. Sixteen schools were purposively selected to participate in the study and randomly allocated as intervention (eight schools) and control (eight schools).The primary aims of HealthKick are to promote healthful eating habits and increase regular participation in health-enhancing physical activity in children, parents and teachers, to prevent overweight, and reduce risk of chronic diseases (particularly type 2 diabetes); as well as to promote the development of an environment within the school and community that facilitates the adoption of healthy lifestyles.The components of HealthKick are: action planning, toolkit (resource guide, a resource box and physical activity resource bin), and an Educators' Manual, which includes a curriculum component.

DISCUSSION

This study continues to highlight the key role that educators play in implementing a school-based intervention, but that developing capacity within school staff and stakeholders is not a simple or easy task. In spite of the challenges experienced thus far, valuable findings are being produced from this study, especially from Phase 1. Materials developed could be disseminated to other schools in low-income settings both within and outside of South Africa. Owing to the novelty of the HealthKick intervention in low-income South African primary schools, the findings of the evaluation phase have the potential to impact on policy and practice within these settings.

A pilot investigation of load-carrying on the head and bone mineral density in premenopausal, black African women

Although the influence of weight-bearing activity on bone mass has been widely investigated in white women, few studies have been conducted in black, African populations. We investigated bone mineral density (BMD) in black South African women, with and without a history of load-carrying on the head. We also investigated whether load carrying may offer protection against low BMD in users of injectable progestin contraception (IPC). Participants were 32 black, South African women (22.4 +/- 3.2 years). Load carrying history was determined by questionnaire and interview; participants were grouped as load carriers (LC; n = 18) or non-load carriers (NLC; n = 14). Ten women were using IPC and 6 were load-carriers. Total body (TB), lumbar spine (LS) and total hip (H) BMD were measured by dual energy X-ray absorptiometry. There were no differences in BMD between LC and NLC, and after controlling for age and BMI using two-tailed partial correlations. IPC users had lower BMD at all sites compared to non-IPC users (p < 0.05) and there were no associations between load carrying and BMD in this group. When IPC users were excluded from analysis, LC had higher LS BMD than NLC (p < 0.005). Correlations were found between the weight of load carried and LS BMD (r = 0.743, p < 0.005), and between years of load carrying and LS and TB BMD (r = 0.563, r = 0.538, respectively; both p < 0.05). Load carrying on the head may offer osteogenic benefits to the spine but these benefits did not appear in women using IPC.

Comparison of site-specific bone mass indices in South African children of different ethnic groups

This study reports on ethnic differences in bone mass before and after adjusting for differences in body size and bone area (BA). Lumbar spine (LSBMC), proximal femur (PFBMC) and femoral neck (FNBMC) bone mineral contents were measured in black ('black'; n = 263) and white ('white'; n = 73) children from Johannesburg and children of mixed ancestral origin ('mixed'; n = 64) from Cape Town, South Africa. Geometric estimates and the power coefficient from the regression analyses of BMC on BA were calculated. After adjusting for age, weight, and height, LSBMC in girls and FNBMC in girls and boys were greatest in mixed, followed by black and then white, groups. Mixed boys and girls also had greater PFBMC than their black and white peers, but only in the boys was PFBMC greater in the black than the white groups. When including BA in the adjustment, differences remained at the FN in boys and girls, and the LS and PF in girls, but disappeared at the PF in mixed and black boys. The difference in LSBMC between mixed and black boys became significant after adjustment for age, weight, height, and BA. Geometric estimates at the femoral neck were greater in the mixed group. Power coefficients were greater in the white group, suggesting differences in shape or bone distribution. In conclusion, this study suggests that, in addition to differences in BMC, differences in bone strength and geometry are present which might confer advantages to the bone of mixed-ancestry children.

Cortical bone development in black and white South African children: iliac crest histomorphometry

Fragility fracture rates in South Africa are lower in blacks (B) than in whites (W) both in adults and in children. In adults this difference may in part be explained by histomorphometric findings in iliac crest cortical bone of B of thicker, less porous cortices, greater endocortical (Ec) wall thickness, fewer canals and greater osteoid thickness accompanied by greater mineral apposition rate and bone formation rate compared to W. Since no comparative data for B and W children are available we examined iliac crest cortical bone of 57 B and 56 W aged 0-23 yrs by routine histomorphometry.

RESULTS

The effects of growth as expressed in differences between external and internal cortex were similar in B and W children. Cortical thickness increased with age similarly in B and W until about age 15 whereafter it continued to increase only in B. Ec wall thickness rose with age in B but did not change in W. After age 11 canal number was lower in B. Cortical porosity was highest between ages 6 and 15 with a tendency to lower values in the external cortex in B. Thus structural differences reported in adults were evident in children. Bone turnover as reflected in osteoid surface and eroded surface declined with age similarly in B and W but osteoid thickness did not change with age. Greater osteoid thickness in B children could reflect greater vigor of osteoblasts and greater osteoblast team performance as it did in B adults and may have contributed to the structural advantage in B children.

CONCLUSION

B children showed greater values for osteoid thickness, endocortical wall thickness and cortical thickness, and a tendency to lower porosity compared to W children. These features may contribute to lower fragility fracture rates in B children. Differing environmental influences and possibly genetic effects may play a role.

Fracture rates in urban South African children of different ethnic origins: the Birth to Twenty cohort

Fracture rates were compared in children of different ethnic backgrounds from Johannesburg, South Africa. More white children fracture than black and mixed ancestry children. Reasons for this may be due to greater sports participation by whites and genetic protective factors in blacks. This has to be further investigated.

INTRODUCTION

Fracture rates in childhood are as high as those in the elderly. Recent research has been undertaken to understand the reasons for this, but there is little information available on ethnic differences in childhood fracture rates.

METHODS

Using the birth to twenty longitudinal cohort of children, we retrospectively obtained information on fractures and their sites from birth to 14.9 years of age on 2031 participants. The ethnic breakdown of the children was black (B) 78%, white (W) 9%, mixed ancestry (MA) 10.5% and Indian (I) 1.5%.

RESULTS

Four hundred and forty-one (22%) children had sustained a fracture one or more times during their lifetime (males 27.5% and females 16.3%; p < 0.001). The percentage of children fracturing differed between the ethnic groups (W 41.5%, B 19%, MA 21%, I 30%; p < 0.001). Of the 441 children reporting fractures, 89(20%) sustained multiple fractures. The most common site of fracture was the upper limb (57%).

CONCLUSION

More white children fracture than black and mixed ancestry children. This is the first study to show ethnic differences in fracture rates among children. The reasons for these differences have to be further elucidated. Greater sports participation by whites and genetic protective factors in blacks may be contributing factors.

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.

Current socio-economic measures, and not those measured during infancy, affect bone mass in poor urban South african children

Understanding the impact of socio-economic status (SES) on physical development in children is important, especially in developing countries where considerable inequalities persist. This is the first study to examine the association between SES on bone development at the whole body, femoral neck, and lumbar spine in black children living in Soweto and Johannesburg, South Africa. Linear regression models were used to study associations between SES during infancy and current SES, anthropometric, and DXA-derived bone mass in 9/10-yr-old children (n = 309). Findings suggest that current SES measures, rather than SES during infancy, are stronger predictors of current whole body bone area (BA) and whole body BMC after adjusting for body size, pubertal development, physical activity, habitual dietary calcium intake, and body composition. SES had no significant effect on either hip or spine bone mass. Caregiver's marital/cohabiting status (indicator of social support) and whether there was a television in the home (indicator of greater income) at age 9/10 yr were the most important socio-economic determinants of whole body BA and BMC. SES has a significant independent effect on whole body BMC through its impact on BA. This suggests that poverty alleviation policies in South Africa could have a positive effect on bone health.

CRHR1 polymorphisms predict bone density in survivors of acute lymphoblastic leukemia

PURPOSE

Corticosteroids are a critical component of therapy for acute lymphoblastic leukemia (ALL) but are associated with late effects, such as osteoporosis. Risk factors remain poorly defined. Because CRHR1 polymorphisms have been associated with other corticosteroid effects, our goal was to define whether CRHR1 polymorphisms predict which patients with ALL are likely to develop bone mineral deficits.

PATIENTS AND METHODS

The mean bone mineral density z scores of 309 long-term survivors of ALL were determined by quantitative computed tomography of the trabecular lumbar spine. We analyzed whether CRHR1 genotypes, adjusted for sex, ALL treatment regimen, and weight, could predict bone density.

RESULTS

We found that three single nucleotide polymorphisms (SNPs), all in linkage disequilibrium, were associated with bone density in a sex-specific manner. Bone density was lower in males (P = .001), in nonblack patients (P < .08), in those who were not overweight (P < .001), and in those who received intensive antimetabolites and glucocorticoids (P < .001). After adjustment for these features, the G allele at the rs1876828 SNP was associated with lower z scores (P = .02) in males but tended to have the opposite association in females (P = .09).

CONCLUSION

CRHR1 polymorphisms may impact the risk of bone density deficits in patients treated with corticosteroids and antimetabolites in a sex-specific manner.

Comparisons of body size, composition, and whole body bone mass between North American and South African children

We compared whole body BMC of 811 black, white, and mixed ancestral origin children from Detroit, MI; Johannesburg, South Africa; and Cape Town, South Africa. Our findings support the role of genetic and environmental influences in the determination of bone mass in prepubertal children.

INTRODUCTION

Higher bone mass and lower fracture rates have been shown in black compared with white children and adults in North America.

MATERIALS AND METHODS

We compared whole body BMC (WBBMC), whole body fat mass (WBFM), and whole body fat free soft tissue (WBFFST) data between three ethnic groups of children from Detroit, MI (n = 181 white, USW; n = 230 black, USB), Johannesburg, South Africa (n = 73 white, SAW; n = 263 black, SAB), and Cape Town, South Africa (n = 64 mixed ancestral origin, SAM).

RESULTS

SAB and SAW groups were slightly older than USW and USB groups (9.5 +/- 0.3 versus 9.3 +/- 0.1 yr); however, USB and USW boys were significantly taller, were heavier, and had a higher BMI than SAM and SAB boys. USB girls were significantly taller than SAB girls and heavier than SAB and SAM girls. In South Africa and the United States, black children had a significantly higher WBBMC than white children, after adjusting for selected best predictors. After adjusting for age, weight, and height, WBBMC was significantly higher in the SAB and SAW boys than in USW and USB and in the SAM group compared with the USW and USB groups. WBFFST and WBFM made significant contributions to a best linear model for log(WBBMC), together with age, height, and ethnicity. The best model accounted for 79% of the WBBMC variance. When included separately in the model, the model containing WBFFST accounted for 76%, and the model containing WBFM accounted for 70%, of the variance in WBBMC.

CONCLUSIONS

WBBMC is lower in children of European ancestry compared with African ancestry, irrespective of geographical location; however, South African children have significantly higher WBBMC compared with USB and USW groups, thereby acknowledging the possible contribution of environmental factors. Reasons for the significantly higher WBBMC in the children of mixed ancestral origin compared with the other groups need to be studied further.

Physical activity, calcium intake and bone health in children and adolescents

Osteoporosis is a serious and potentially debilitating disease, which can lead to a variety of health complications and a diminished quality of life. Consequently, the development of bone mineral density (BMD) and content (BMC) during childhood and adolescence is of great importance, as it may attenuate the effects and incidence of osteoporosis later in life. Identifying the mechanisms by which bones are strengthened early in life is crucial. This review highlights research examining factors that influence BMD and BMC in children and adolescents. While a sizeable amount of variation in BMD and BMC in children and adolescents can be attributed to genetic factors and body size, studies have also shown the positive influence of physical activity and calcium intake on bone development. Research supporting the role of these modifiable factors varies according to age, sex and the bone site studied. During the pubertal years, large gains in BMD and BMC are evident. However, physical activity and calcium intake are also important to the development of BMD and BMC during the prepubertal years. Thus, actions taken throughout childhood may exert a great impact on BMD and BMC, and overall bone health as an adult.

Infant programming of bone size and bone mass in 10-year-old black and white South African children

In developed countries, the earliest of factors shown to identify those at a high risk of having low bone mass and so be prone to osteoporosis in later life is that of quality of early life reflected by low birthweight (BW) and size in infancy. It is unclear whether such relationships exist in developing countries and in black populations. Associations were studied between BW, weight (WT1) and length (LT1) at 1 year and bone size and bone mass in 476 children (boys: 182 black, 72 white; girls: 158 black, 64 white) aged 10 years, who formed part of a longitudinal cohort of children born in Johannesburg, South Africa, during 1990. Bone area (BA) and bone mineral content (BMC) measurements were made of the whole body, femoral neck and lumbar spine (L1-L4) by dual-energy X-ray absorptiometry (DXA). After adjusting BA and BMC for race, gender, age, socio-economic status, bone age, height and weight at 10 years, on which BA and BMC in children are so dependent, WT1, LT1 and BW were significant predictors of whole body BA (WT1, P < 0.0001; LT1, P < 0.01; BW, P < 0.05) and BMC (WT1, P < 0.01; LT1, P < 0.05; BW, P < 0.05) and of BMC of the femoral neck (WT1, P < 0.01; LT1, P < 0.05). When BMC was in addition corrected for BA, then BW, WT1 and LT1 were predictive of femoral neck BMC (BW, P < 0.05; WT1, P < 0.05; LT1, P < 0.01) but not whole body BMC. Thus, BMC at 10 years appears to be independently associated with weight and length at 1 year, which is not completely mediated by the tracking of skeletal growth. Low BW and small size at 1 year resulted in smaller bones and/or bones of lower BMC at the femoral neck. The findings support the hypothesis that growth and development, both intrauterine and in the first year, which are measures of genetic, intrauterine and postnatal environmental factors, may have long-term consequences when compromised, and may be associated with the risk of osteoporosis in later life.

Bone mass accretion rates in pre- and early-pubertal South African black and white children in relation to habitual physical activity and dietary calcium intakes

AIM

To examine bone mass changes in 321 black and white South African children in relation to habitual physical activity (PA) levels and calcium intakes.

METHODS

Children underwent two bone mass scans at ages nine and 10 years using dual X-Ray absorptiometry. PA levels and calcium intakes were assessed using questionnaires. Data were analyzed by regressing change in bone mineral content (BMC) and bone area (BA) from age nine to 10, against BA (for BMC), height and body weight. The residuals were saved and called residualized BMCGAIN and BAGAIN. Residualized values provide good indication of weight, height and BA-matched accumulation rates.

RESULTS

White children had significantly higher PA levels and calcium intakes than black children. Most active white males had significantly higher residualized BMCGAIN and BAGAIN at the whole body, hip and spine but not at the radius, than those who were less active. Most active white females had significantly higher residualized BAGAIN at all sites except the radius than less-active girls. No such effects were seen in black children. There was no interactive effect on residualized BMCGAIN for calcium intake and PA (except at the spine in white girls).

CONCLUSION

Bone mass and area gain is accentuated in pre- and early-pubertal children with highest levels of habitual physical activity. Limited evidence of an effect of dietary calcium intakes on BMC was found.

Differences in bone size and bone mass between black and white 10-year-old South African children

INTRODUCTION

Black and white South Africans hail from vastly disparate cultural and socio-economic backgrounds the result of which exposes black children to numerous factors known to impact negatively on bone mass. Thus, we studied ethnic differences in bone size and bone mass between 476 10-year-old black and white South African girls and boys (black boys n=182, white boys n=72, black girls n=158, white girls n=64) who formed part of a longitudinal cohort of children born in Johannesburg, South Africa, during 1990.

METHODS

Bone area (BA) and bone mineral content (BMC) were measured at the whole body, total hip, femoral neck, lumbar spine (L1-L4) and mid- and distal radii by dual energy X-ray absorptiometry (DXA). Vertebral heights and metacarpal indices were measured. Anthropometry, skeletal maturity and pubertal development were also assessed.

RESULTS

After correction for height, weight, gender and puberty, black children had greater BMC at the femoral neck (P<0.0001), total hip (P<0.05) and mid-radius (P<0.001) than white children.. At the whole body, lumbar spine, and distal one-third of the radius, there were no differences in BMC between black and white children after correction for differences in body size. After correction for height and puberty, vertebral heights were less in black children than white children, and cortical areas at the second metacarpal were greater in black children.

CONCLUSION

These findings suggest that, at the femoral neck, total hip and mid-radius, these differences are not a result of differences in anthropometry, bone age or pubertal stage, or environmental factors but are most likely to result from genetic differences.