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

Bone health index in the assessment of bone health: The Generation R Study

Bone Health Index (BHI) has been proposed as a useful instrument for assessing bone health in children. However, its relationship with fracture risk remains unknown. We aimed to investigate whether BHI is associated with bone mineral density (BMD) and prevalent fracture odds in children from the Generation R Study. We also implemented genome-wide association study (GWAS) and polygenic score (PGS) approaches to improve our understanding of BHI and its potential. In total, 4150 children (49.4 % boys; aged 9.8 years) with genotyped data and bone assessments were included in this study. BMD was measured across the total body (less head following ISCD guidelines) using a GE-Lunar iDXA densitometer; and BHI was determined from the hand DXA scans using BoneXpert®. Fractures were self-reported collected with home questionnaires. The association of BHI with BMD and fractures was evaluated using linear models corrected for age, sex, ethnicity, height, and weight. We observed a positive correlation between BHI and BMD (ρ = 0.32, p-value<0.0001). Further, every SD decrease in BHI was associated with an 11 % increased risk of prevalent fractures (OR:1.11, 95 % CI 1.00-1.24, p-value = 0.05). Our BHI GWAS identified variants (lead SNP rs1404264-A, p-value = 2.61 × 10-14) mapping to the ING3/CPED1/WNT16 locus. Children in the extreme tails of the BMD PGS presented a difference in BHI values of -0.10 standard deviations (95% CI -0.14 to -0.07; p-value<0.0001). On top of the demonstrated epidemiological association of BHI with both BMD and fracture risk, our results reveal a partially shared biological background between BHI and BMD. These findings highlight the potential value of using BHI to screen children at risk of fracture.

Bone mass and vertebral fractures in South African children on prolonged oral glucocorticoids for chronic non-malignant illnesses

Introduction

We hypothesized that the prevalence of vertebral fractures would be low and that bone mineral density (BMD) would be less severely affected in a black South African (SA) population treated with glucocorticoids (GCs) than that reported in mainly white populations.

Methods

All children aged 5–17.9 years with chronic non-malignant illnesses who were on GCs (intravenous or oral) for greater than 3 months duration were evaluated. DXA scans were performed using a Hologic Discovery machine (Software version Apex 4.0.2) and the Hologic paediatric reference database. Whole body less head (WBLH) and lumbar spine (LS) bone mineral content (BMC) and density (BMD) Z-scores unadjusted and adjusted for height were calculated using the Zemel equation calculator.

Results

Seventy-two patients (49% with renal, 24% with rheumatic, 14% with neurological, 11% with hepatic and 3% with respiratory conditions; mean age 11.6 ± 3.3 years, 57% boys, 92% SA black) were enrolled. The mean duration of GC treatment was 34.1 (±25.1) months. Mean WBLH and LS height adjusted BMD Z-scores were −1.2 ± 1.5 and −0.9 ± 1.0 respectively. Eleven percent of patients had a LS height adjusted BMD Z-score ≤ −2. The prevalence of vertebral fractures on lateral vertebral fracture assessment (VFA) was 15% (11 of 72 patients).

Conclusion

The prevalence of vertebral fractures (15%) in predominantly black children on GCs with chronic non-malignant illnesses is similar to that reported from North America suggesting that routine yearly DXA scans including VFA are warranted in this highly at-risk population.

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Prevalence of vertebral fractures in black South African children on GCs is 15%.

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Majority of patients had 25(OH)D levels >30 nmol/L.

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A quarter of the patients with vitamin D deficiency had a LS BMD Z score ≤ −2.

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None of the vitamin D deficient patients had vertebral fractures.

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Routine yearly DXA scans are thus warranted on all children treated with GCs.

Testing the cross-applicability of juvenile sex estimation from diaphyseal dimensions

Sex estimation is a crucial component of the biological profile. Stull et al. (2017) have proposed a promising juvenile sex estimation method using long bone measurements taken from a South African sample, providing relatively high classification accuracies and made easy to use via the KidStats web-based app. In this study, we test the models developed by Stull et al. (2017) on an external historic population from Lisbon, Portugal, in order to determine whether the models can be reliably applied to archeological and forensic populations outside of the original population sample. The study sample consisted of 102 individuals (45 females and 57 males) aged under 13 years at death from the Lisbon identified skeletal collection. Measurements from these individuals were used to test the flexible discriminant analysis (FDA) models given by Stull et al. (2017). Allocation accuracies were calculated for boys and girls and children over and under 2 years separately and combined. Our findings show that the models developed by Stull et al. (2017) yield poor accuracy when applied to our external population and thus can potentially be misapplied on archeological skeletal remains or forensic remains of unknown origin. A number of statistical issues may explain why models fail to be transportable or even generalizable, namely multicollinearity, model overfitting and overly optimist bootstrapped cross-validation rates. It is also likely that population differences in size and sexual size dimorphism also affected the applicability of the models. We emphasize the importance of externally validating prediction models, particularly if they are intended to be applied across populations. Our study addresses Stull and co-worker's request for further validation of the method on populations outside of South Africa, as the models cannot be confidently applied in the field until it has been externally validated.

The Demographics of Fractures and Dislocations Across the Entire United States due to Common Sports and Recreational Activities

BACKGROUND

There exists little nationwide data regarding fracture and dislocation patterns across a wide variety of sporting activities for all ages and sexes.

HYPOTHESIS

Participant demographics (age and sex) will vary with regard to fracture and joint dislocation sustained during sport-related activities.

STUDY DESIGN

Descriptive epidemiology study.

LEVEL OF EVIDENCE

Level 3.

METHODS

The National Electronic Injury Surveillance System All Injury Program data 2005 through 2013 were accessed; 18 common sports and recreational activities in the United States were selected. Statistical software was used to calculate the numbers of fractures and dislocations, and incidence was calculated using US Census Bureau data. Multivariate logistic regression analysis determined the odds ratios (ORs) for the occurrence of a fracture or dislocation.

RESULTS

A fracture occurred in 20.6% and a joint dislocation in 3.6% of the emergency department visits for sports-related injuries; annual emergency department visit incidence was 1.51 for fractures and 0.27 for dislocations (per 1000 people). Most of the fractures occurred in football (22.5%). The OR for fracture was highest for inline skating (OR, 6.03), males (OR, 1.21), Asians, whites, and Amerindians compared with blacks (OR, 1.46, 1.25, and 1.18, respectively), and those older than 84 years (OR, 4.77). Most of the dislocations occurred in basketball (25.7%). The OR for dislocation was highest in gymnastics (OR, 4.08), males (OR, 1.50), Asians (OR, 1.75), and in those aged 20 to 24 years (OR, 9.04). The most common fracture involved the finger, and the most common dislocation involved the shoulder.

CONCLUSION

Inline skating had the greatest risk for fracture, and gymnastics had the greatest risk for joint dislocation.

CLINICAL RELEVANCE

This comprehensive study of the risks of sustaining a fracture or dislocation from common sports activities across all age groups can aid sports health providers in a better understanding of those sports at high risk and be proactive in prevention mechanisms (protective gear, body training).

Metacarpal Indices and Their Association with Fracture in South African Children and Adolescents

This prospective study assessed whether metacarpal indices predict fracture risk in children and adolescents. Radiogrammetry was performed at the second metacarpal midshaft on annual hand-wrist radiographs of 359 South African (SA) children aged 10-17 years. Bone length, bone width, and medullary width were measured, and the following proxies for bone strength calculated: metacarpal index (MCI), bone mineral density (BMD), section modulus (SM), stress-strain index (SSI), and slenderness index (SLI). Height and weight were measured annually. Self-reported physical activity (PA) and fracture history were obtained at ages 15 years (for the preceding 12 months) and 17 years, respectively. At 17 years, 82 (23%) participants (black, 16%; white, 42%; p < 0.001) reported a previous fracture. None of the bone measures or indices were associated with fracture in black participants. In white females, after adjusting for PA, a 1 standard deviation (SD) greater SLI doubled the fracture risk [odds ratio (OR) 2.08; 95% confidence interval (CI) 1.08, 3.98]. In white males, a 1 SD greater BMD was associated with a 2.62-fold increase in fracture risk (OR 3.62; 95% CI 1.22, 10.75), whilst a 1 SD greater SM (OR 2.29; 95% CI 1.07, 4.89) and SSI (OR 2.23; 95% CI 1.11, 4.47) were associated with a more than twofold increase in fracture risk, after height, and PA adjustment. No single index consistently predicted fracture across the four groups possibly due to ethnic and sex differences in bone geometry, muscle mass, and skeletal loading. Metacarpal radiogrammetry did not reliably predict fracture in SA children.

Relative contributions of lean and fat mass to bone strength in young Hispanic and non-Hispanic girls

BACKGROUND

With the high prevalence of childhood obesity, especially among Hispanic children, understanding how body weight and its components of lean and fat mass affect bone development is important, given that the amount of bone mineral accrued during childhood can determine osteoporosis risk later in life. The aim of this study was to assess the independent contributions of lean and fat mass on volumetric bone mineral density (vBMD), geometry, and strength in both weight-bearing and non-weight-bearing bones of Hispanic and non-Hispanic girls.

METHODS

Bone vBMD, geometry, and strength were assessed at the 20% distal femur, the 4% and 66% distal tibia, and the 66% distal radius of the non-dominant limb of 326, 9- to 12-year-old girls using peripheral quantitative computed tomography (pQCT). Total body lean and fat mass were measured by dual-energy x-ray absorptiometry (DXA). Multiple linear regression was used to assess the independent relationships of fat and lean mass with pQCT bone measures while adjusting for relevant confounders. Potential interactions between ethnicity and both fat and lean mass were also tested.

RESULTS

Lean mass was a significant positive contributor to all bone outcomes (p < 0.05) with the exception of vBMD at diaphyseal sites. Fat mass was a significant contributor to bone strength at weight bearing sites, but did not significantly contribute to bone strength at the non-weight bearing radius and was negatively associated with radius cortical content and thickness. Bone measures did not significantly differ between Hispanic and non-Hispanic girls, although there was a significant interaction between ethnicity and fat mass with total bone area at the femur (p = 0.02) and 66% tibia (p = 0.005) as well as bone strength at the femur (p = 0.03).

CONCLUSION

Lean mass is the main determinant of bone strength for appendicular skeletal sites. Fat mass contributes to bone strength in the weight-bearing skeleton but does not add to bone strength in non-weight-bearing locations and may potentially be detrimental. Bone vBMD, geometry, and strength did not differ between Hispanic and non-Hispanic girls; fat mass may be a stronger contributor to bone strength in weight-bearing bones of Hispanic girls compared to non-Hispanic.

Metacarpal Growth During Adolescence in a Longitudinal South African Cohort

To monitor the drift of the periosteal and endocortical surfaces during metacarpal growth longitudinally, radiogrammetry was carried out on hand-wrist X-rays of 572 children from the Birth to Twenty Bone Health Cohort annually from ages 9 to 21 years. This is the largest collection of longitudinal X-rays in African children. The second metacarpal bone length, bone width, and medullary width were measured using digital vernier calipers on a total of 4730 X-rays. Superimposition by Translation and Rotation (SITAR) was used to obtain age at peak metacarpal length velocity (PLV). Bone width and medullary width were modeled using SITAR against both chronological age and age from PLV. In black and white females, tempo and velocity of metacarpal length growth was synchronized. Black males, however, attained PLV 7 months later than white males (p < 0.0001). Compared to white males, black males had a longer second metacarpal (p < 0.05), and greater bone width size (p < 0.02), tempo (p < 0.0009), and velocity (p < 0.0001). Medullary width growth velocity in black participants peaked 2 years prior to attainment of PLV and exceeded that of their white peers (p < 0.0001) in whom it peaked 6 to 12 months post-PLV attainment. Black adolescents therefore had wider bones with relatively thinner cortices and wider medullary cavities than their white peers. Ethnic and sex differences also occurred in the timing of medullary width contraction that accompanied expansion in bone width and cortical thickness. In black males, medullary width contraction commenced approximately 3 years later than in black females, whereas in white males this occurred a year later than in white females. The ethnic and sex differences in bone acquisition reported in this study may differentially affect bone mass in later life. © 2017 American Society for Bone and Mineral Research.

Bone health of the Ovahimba people of north-western Namibia in the context of urbanization and a change of the sociocultural environment

The prevalence of osteoporosis in Sub-Saharan African (SSA) countries is low, however, as urbanization takes root, it is predicted that bone health will decrease dramatically. The bone health of the semi-nomadic Ovahimba people of Namibia was investigated in the context of urbanization and changes of the sociocultural environment. Furthermore, data on bone health in SSA countries is scarce; there exists no ethnic-specific reference group for people of black origin. Included in the study were 98 urban and rural living Ovahimba people. Quantitative ultrasound was performed, sunrise/sunset saliva cortisol concentrations was measured and a questionnaire was conducted. There was no significant difference in the QUS parameters, however, after adjustment for confounders, SOS and SI differed significantly. The saliva cortisol concentrations differed significantly. After adjustment for confounders, saliva cortisol was significantly negatively correlated to SOS (r= -0.27, p = 0.021) giving an indication for an association between cortisol concentration and QUS parameters. The urban group furthermore showed a nutritional transition. Even though the bone health of the Ovahimba is very good, first signs of the adverse effects of urbanization were detected. Beside changes of lifestyle, this may be attributed to an increased cortisol exposure of the Ovahimba people living in an urban environment due to an increased psychosocial stress.

A radiographic investigation of the relationships between humeral cortical bone thickness, medullary canal width and the supratrochlear aperture (STA)

The supratrochlear aperture (STA) is a perforation of the septum between the olecranon and coronoid fossae of the humerus. Bones with STA are prone to supracondylar fractures and are thought to have narrower medullary canals. Our aim was to explore the relationship of the STA with medullary canal width and humeral size. The study employed a case-control research design with approximately equal numbers of individuals with and without STA from South African Whites, Blacks, and the Mixed ethnic group. Radiographs were taken anteroposteriorly using a Lodox Statscan and Image J^® software was used to acquire measurements from the radiographs. In the proximal diaphysis, the mean medullary canal width was significantly smaller for STA humeri (13.59 vs. 14.72 mm). The same was true for the midshaft (10.21 vs. 10.84 mm) and the distal portion (10.05 vs. 10.63 mm). While STA humeri appeared to have narrower medullary canal dimensions, this was not the case after standardizing for bone size. The smaller medullary canal width reported in the literature for STA-bearing humeri is, therefore, due to bone size differences and not STA presence. This is supported by the strong positive correlation between bone size and medullary canal width irrespective of STA status. Thus, the medullary canal width increases with bone size independent of STA status. We, therefore, propose that bone size, and not STA presence, is the major factor to consider when choosing rods for intramedullary fixation.

Does vitamin D status track through adolescence?

BACKGROUND

To our knowledge, no studies have reported on the long-term variability of vitamin D status in adolescents.

OBJECTIVE

To determine whether tracking of vitamin D status occurs in healthy adolescents, we assessed the variability of 25-hydroxyvitamin D [25(OH)D] every 2 y over a 10-y period in a longitudinal cohort of adolescents living in Johannesburg, South Africa (latitude 26°S).

DESIGN

Healthy adolescents who had blood samples available on ≥3 occasions between 11 and 20 y of age were included in the study. Of the cohort of 504 children, 99 met the criteria. The mean 25(OH)D concentration at each time point was measured, and the individual 25(OH)D z scores based on year 11 values were used as the reference. All 25(OH)D concentrations for a subject were measured in a single assay.

RESULTS

No significant correlation was found between 25(OH)D in the earlier and later years of adolescence, although significant correlations were found between year 11 and year 13 (r = 0.71, P < 0.0001) and between years 15, 17, and 20 (r ≥ 0.65, P < 0.0001). The percentage of adolescents whose 25(OH)D concentration changed by >20 nmol/L from year 11 was calculated for all age groups: 12% of the cohort had a change of >20 nmol/L at 13 y of age compared with 46% at 20 y of age. Just more than one-half (53%) of the cohort changed their category of vitamin D status between the ages of 11 and 20 y, and one-third of adolescents changed from being replete to insufficient over the same period.

CONCLUSIONS

The data suggest that the measurement of 25(OH)D at a single time point does not reflect the long-term vitamin D status of an adolescent. These findings may cast doubt on the veracity of those studies that suggest an association of vitamin D status with various disease states in which vitamin D status was measured only once.

Calcium and vitamin D metabolism in children in developing countries

Low dietary calcium intakes and poor vitamin D status are common findings in children living in developing countries. Despite many of the countries lying within the tropics and subtropics, overcrowding, atmospheric pollution, a lack of vitamin D-fortified foods, and social customs that limit skin exposure to sunlight are major factors in the development of vitamin D deficiency. Low dietary calcium intakes are typically observed as a consequence of a diet limited in dairy products and high in phytates and oxalates which reduce calcium bioavailability. Calcium intakes of many children are a third to a half of the recommended intakes for children living in developed countries, yet the consequences of these low intakes are poorly understood as there is limited research in this area. It appears that the body adapts very adequately to these low intakes through reducing renal calcium excretion and increasing fractional intestinal absorption. However, severe deficiencies of either calcium or vitamin D can result in nutritional rickets, and low dietary calcium intakes in association with vitamin D insufficiency act synergistically to exacerbate the development of rickets. Calcium supplementation in children from developing countries slightly increases bone mass, but the benefit is usually lost on withdrawal of the supplement. It is suggested that the major effect of calcium supplementation is on reducing the bone remodelling space rather than structurally increasing bone size or volumetric bone density. Limited evidence from one study raises concerns about the use of calcium supplements in children on habitually low calcium intakes as the previously supplemented group went through puberty earlier and had a final height several centimetres shorter than the controls.

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.

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.

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.

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.

Systematic review of birth cohort studies in Africa

AIM

In sub-Saharan Africa, unacceptably high rates of mortality amongst women and children continue to persist. The emergence of research employing new genomic technologies is advancing knowledge on cause of disease. This review aims to identify birth cohort studies conducted in sub-Saharan Africa and to consider their suitability as a platform to support genetic epidemiological studies.

METHODS

A systematic literature review was conducted to identify birth cohort studies in sub-Saharan Africa across the following databases: MEDLINE, EMBASE, AFRO and OpenSIGLE. A total of 8110 papers were retrieved. Application of inclusion/exclusion criteria retained only 189 papers, of which 71 met minimum quality criteria and were retained for full text analysis.

RESULTS

The search revealed 28 birth cohorts: 14 of which collected biological data, 10 collected blood samples and only one study collected DNA for storage. These studies face many methodological challenges: notably, high rates of attrition and lack of funding for several rounds of study follow up. Population-based 'biobanks' have emerged as a major approach to harness genomic technologies in health research and yet the sub-Saharan African region still awaits large scale birth cohort biobanks collecting DNA and associated health and lifestyle data.

CONCLUSION

Investment in this field, together with related endeavours to foster and develop research capacity for these studies, may lead to an improved understanding of the determinants of intrauterine growth and development, birth outcomes such as prematurity and low birth weight, the links between maternal and infant health, survival of infectious diseases in the first years of life, and response to vaccines and antibiotic treatment.

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.

Vitamin D and adolescent health

Vitamin D is a hormone sequentially produced at different body sites, and which plays a significant role in human health, particularly bone health. However, other roles are emerging. When the serum concentration of vitamin D is very low, the risk of rickets, osteomalacia and osteoporosis is increased. In children and adolescents there is a high prevalence of low vitamin D status, especially in females and during the winter–the prevalence being lower than during the summer. Although there is no unanimous agreement over the minimum values necessary for good health, serum 25-hydroxyvitamin D [25(OH)D] levels below 20 ng/mL may be regarded as a vitamin D-deficient condition, and levels between 20–30 ng/mL may be the range of vitamin D insufficiency. Mild low levels have been associated with bone mass accrual alterations in children and adolescents, diminished muscle strength, negative cardiovascular outcomes, insulin resistance and obesity, and neurological disorders. Effective preventive strategies are needed to guarantee adequate vitamin D levels throughout childhood and adolescence, taking into account the geographical setting, season of the year, the level of environmental pollution, skin characteristics, eating habits and body weight, with a view to securing optimum health during these phases, and the prevention of complications in adulthood. There needs to be a renewed appreciation of the beneficial effect of moderate sunlight for providing all humans with the vitamin D needed for ensuring good health. Prolonged sun exposure is not advised, however, due to the risk of skin cancer. In addition, a balanced diet is indicated, since vitamin D-rich foods are better assimilated than supplements. When such conditions cannot be met, then the supplementation of 400 IU/day of vitamin D is advised in children and adolescents–though correcting vitamin D insufficiency or deficiency may require 1000 IU/day or more. High-dose calcifediol depots are an alternative for guaranteeing treatment adherence and in patients with liver disease.

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.

Quantitative ultrasound in relation to risk factors for low bone mineral density in South African pre-menopausal women

SUMMARY: The study describes the association between risk factors and quantitative ultrasound bone measures in black and mixed-race pre-menopausal South African women. Despite some differences between the two study groups, the findings generally lend support to the use of ultrasound for epidemiological studies of bone mass in resource-limited settings. INTRODUCTION: Quantitative ultrasound at the calcaneus is a convenient and inexpensive method of estimating bone strength well suited to community-based research in countries with limited resources. This study determines, in a large sample of pre-menopausal South African women, whether characteristics associated with quantitative ultrasound measures are similar to those shown to be associated with bone mineral density as measured by dual X-ray absorptiometry. METHODS: This cross-sectional study included 3,493 women (1,598 black and 1,895 mixed race), aged 18-44 living in Cape Town. Study nurses administered structured interviews on reproductive history, lifestyle factors, and measured height and weight. Calcaneus quantitative ultrasound measurements were obtained using the Sahara device. Adjusted means of ultrasound measures according to categories of risk factors were obtained using multivariable regression analysis. RESULTS: Associations between quantitative ultrasound measures and age, body mass index, age at menarche, parity, and primary school physical activity were similar to those known for bone mineral density as measured by dual X-ray absorptiometry. There were no clear associations between quantitative ultrasound measures and educational level, alcohol use, cigarette smoking, and current calcium intake. CONCLUSION: The data give qualified support to the use of quantitative ultrasound as an epidemiological tool in large studies of bone strength in pre-menopausal women.

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.

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.

Use of bioelectrical impedance analysis to assess body composition in rural Gambian children

OBJECTIVE

To validate the Tanita BC-418MA Segmental Body Composition Analyser and four-site skinfold measurements for the prediction of total body water (TBW), percentage fat-free mass (%FFM) and percentage body fat (%BF) in a population of rural Gambian children.

SUBJECTS/METHODS

One hundred and thirty-three healthy Gambian children (65 males and 68 females). FFM estimated by the inbuilt equations supplied with the Tanita system was assessed by comparison with deuterium oxide dilution and novel prediction equations were produced. Deuterium oxide dilution was also used to develop equations for %BF based on four-site skinfolds (biceps, triceps, subscapular and suprailiac).

RESULTS

The inbuilt equations underestimated FFM compared to deuterium oxide dilution in all the sex and age categories (P<0.003), with greater accuracy in younger children and in males. The best prediction of %FFM was obtained from the variables height, weight, sex, impedance, age and four skinfold thickness measurements (adjusted R(2)=0.84, root mean square error (MSE)=2.07%).

CONCLUSIONS

These data suggest that the Tanita instrument may be a reliable field assessment technique in African children, when using population and gender-specific equations to convert impedance measurements into estimates of FFM.

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 age estimation based on phalanx information with fuzzy constrain of carpals

The proposed automatic bone age estimation system was based on the phalanx geometric characteristics and carpals fuzzy information. The system could do automatic calibration by analyzing the geometric properties of hand images. Physiological and morphological features are extracted from medius image in segmentation stage. Back-propagation, radial basis function, and support vector machine neural networks were applied to classify the phalanx bone age. In addition, the proposed fuzzy bone age (BA) assessment was based on normalized bone area ratio of carpals. The result reveals that the carpal features can effectively reduce classification errors when age is less than 9 years old. Meanwhile, carpal features will become less influential to assess BA when children grow up to 10 years old. On the other hand, phalanx features become the significant parameters to depict the bone maturity from 10 years old to adult stage. Owing to these properties, the proposed novel BA assessment system combined the phalanxes and carpals assessment. Furthermore, the system adopted not only neural network classifiers but fuzzy bone age confinement and got a result nearly to be practical clinically.