Maternal and neonatal vitamin D status at birth in black South Africans.

BACKGROUND: Vitamin D deficiency (VDD) in pregnant women has been associated with adverse pregnancy and neonatal outcomes. 25-hydroxyvitamin D (25(OH)D) levels are affected by numerous factors, including vitamin D intake, skin pigmentation, latitude and season of the year; they therefore vary by race and country. Vitamin D status in pregnant women and their offspring in South Africa (SA) is not well established. OBJECTIVES: To assess vitamin D status by measuring serum 25(OH)D in pregnant black SA women and their offspring in Johannesburg (latitude 26°S) and to assess whether vitamin D status is affected by maternal HIV infection. METHODS: We prospectively enrolled pregnant women and their healthy neonates, and measured 25(OH)D in maternal and cord blood at delivery. Pregnant women were stratified by their HIV status. Predictors of maternal and neonatal VDD (levels <30 nmol/L) were assessed using multiple logistic regression analysis. RESULTS: A total of 291 pregnant women and their healthy neonates were enrolled over a 21-month period. Mean (standard deviation) maternal and cord blood 25(OH)D levels were 57.0 (29.7) and 41.9 (21.0) nmol/L and the prevalence of VDD was 15.9% and 32.8%, respectively. On average, concentrations of 25(OH)D in cord blood were ~80% of those in the mother. There was no association between cord 25(OH)D and gestational age, but levels were associated with birth weight (p<0.001). There were no differences in maternal or cord blood 25(OH)D levels between those HIV-infected or uninfected. The predictor of VDD in mothers was giving birth in winter (odds ratio (OR) 2.87, 95% confidence interval (CI) 1.47 - 5.61), and in neonates the predictors were maternal age (OR 16.5, 95% CI 1.82 - 149), being born in winter (OR 3.68, 95% CI 2.05 - 6.61), being born by caesarean section (OR 4.92, 95% CI 1.56 - 15.57) and being of low birth weight (OR 1.99, 95% CI 1.13 - 3.50). CONCLUSIONS: Among black SA women delivering in Johannesburg, about one in six mothers and one in three neonates have 25(OH)D levels indicative of VDD. Maternal HIV status appears not to affect levels of 25(OH)D in either the mother or her neonate. Research on the effects of VDD on the outcomes of pregnancy and the best methods to combat the high prevalence of VDD in women of childbearing age in the SA context is required.

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.

A longitudinal comparison of appendicular bone growth and markers of strength through adolescence in a South African cohort using radiogrammetry and pQCT.

To compare growth patterns and strength of weight- and non-weight-bearing bones longitudinally. Irrespective of sex and ethnicity, metacarpal growth was similar to that of the non-weight-bearing radius but differed from that of the weight-bearing tibia. Weight- and non-weight-bearing bones have different growth and strength patterns. INTRODUCTION: Functional loading modulates bone size and strength. METHODS: To compare growth patterns and strength of weight- and non-weight-bearing bones longitudinally, we performed manual radiogrammetry of the second metacarpal on hand-wrist radiographs and measured peripheral quantitative computed tomography images of the radius (65%) and tibia (38% and 65%), annually on 372 black and 152 white South African participants (ages 12-20 years). We aligned participants by age from peak metacarpal length velocity. We assessed bone width (BW, mm); cortical thickness (CT, mm); medullary width (MW, mm); stress-strain index (SSI, mm3); and muscle cross-sectional area (MCSA, mm2). RESULTS: From 12 to 20 years, the associations between metacarpal measures (BW, CT and SSI) and MCSA at the radius (males R2 = 0.33-0.45; females R2 = 0.12-0.20) were stronger than the tibia (males R2 = 0.01-0.11; females R2 = 0.007-0.04). In all groups, radial BW, CT and MW accrual rates were similar to those of the metacarpal, except in white females who had lower radial CT (0.04 mm/year) and greater radial MW (0.06 mm/year) accrual. In all groups, except for CT in white males, tibial BW and CT accrual rates were greater than at the metacarpal. Tibial MW (0.29-0.35 mm/year) increased significantly relative to metacarpal MW (- 0.07 to 0.06 mm/year) in males only. In all groups, except white females, SSI increased in each bone. CONCLUSION: Irrespective of sex and ethnicity, metacarpal growth was similar to that of the non-weight-bearing radius but differed from that of the weight-bearing tibia. The local and systemic factors influencing site-specific differences require further investigation. Graphical abstract.

The relationship between maternal and child bone density in Nigerian children with and without nutritional rickets.

We found a positive relationship between bone density in Nigerian children with and without rickets and that of their mothers. After treatment, children with rickets had greater bone density than children without rickets, indicating that children genetically programmed to have greater bone density may have a higher risk of rickets. INTRODUCTION: To determine the relationship between bone density in children with and without rickets and that of their mothers METHODS: Using an unmatched case-control design, forearm areal bone mineral density (aBMD) was measured in 52 and 135 Nigerian children with and without rickets and their mothers, respectively. We performed multivariate linear regression analyses to assess the relationship between maternal and child aBMD Z-scores. RESULTS: Forearm aBMD Z-scores in children were associated with maternal aBMD Z-scores at metaphyseal (effect estimate 0.23; 95% CI 0.08 to 0.37) and diaphyseal (effect estimate 0.16; 0.01 to 0.30) sites, after adjustment for rickets in the child, child's age and sex, height-for-age Z-score, and weight-for-age Z-score. In the adjusted model, rickets was inversely associated with child's aBMD Z-score at the diaphyseal site only (- 0.45, - 0.65 to - 0.24). The positive relationship between maternal and child aBMD Z-scores was marginally greater in children with rickets (slope 0.56, r = 0.47) than without rickets (slope 0.19, r = 0.20) at the diaphyseal site only (P = 0.06 for interaction) but not at the metaphyseal site (slopes 0.35 and 0.30, respectively, P = 0.48). After treatment with calcium for 6 months, metaphyseal aBMD Z-scores were greater in children with treated rickets (effect estimate 0.26; 95% CI 0.02 to 0.49) than in those without rickets. CONCLUSION: In Nigerian children with and without rickets, forearm aBMD Z-scores were positively associated with maternal aBMD Z-scores. Active rickets in the child marginally modified the relationship at the diaphyseal site only. After treatment, children with rickets had greater metaphyseal aBMD Z-scores than children without rickets.

A comparison of body composition estimates using dual-energy X-ray absorptiometry and air-displacement plethysmography in South African neonates.

BACKGROUND/OBJECTIVES: Neonatal body composition is an important predictor of future metabolic risk; however, the comparability of objective assessment techniques, particularly in African populations undergoing rapid health transition, is not known. This paper compares body composition estimates by air-displacement plethysmography (ADP) and dual-energy X-ray absorptiometry (DXA) in South African neonates. SUBJECTS/METHODS: Fat mass, fat-free mass and body fat percentage (%fat) estimates by ADP and DXA were compared in 88 urban, black South African neonates. The level of agreement between the techniques was assessed using Bland-Altman analyses. RESULTS: Significant correlations were observed between ADP and DXA measurements of fat mass (r=0.766), fat-free mass (r=0.942) and %fat (r=0.630); however, ADP estimates of fat mass (408±172 g vs 337±165 g; P<0.001) and %fat (12.9±4.4% vs 9.9±4%; P<0.001) were significantly higher and fat-free mass (2681±348 g vs 2969±375 g; P<0.001) significantly lower than those by DXA. Fat-free mass estimates showed greater consistency in the level of agreement between the techniques compared with fat and %fat estimates where the differences between methods were less predictable. CONCLUSION: Although ADP and DXA body composition estimates are highly correlated in neonates, significant differences are observed between the techniques. This is particularly relevant for fat mass and %fat estimates, where differences are highly variable between methods. Further investigation is needed to minimise inter-method differences to ensure accurate and comparable assessment of body composition at birth and across longitudinal study follow-up.

Even transient rapid infancy weight gain is associated with higher BMI in young adults and earlier menarche.

BACKGROUND: Early postnatal rapid 'catch-up' weight gain has been consistently associated with subsequent higher obesity risk and earlier pubertal development. In many low- and middle-income countries, infancy catch-up weight gain is transient and often followed by growth faltering. We explored the hypothesis that even transient catch-up weight gain during infancy is associated with later obesity risk and earlier puberty. METHODS: A total of 2352 (1151 male, 1201 female) black South African children in the birth to twenty prospective birth cohort study (Johannesburg-Soweto) underwent serial measurements of body size and composition from birth to 18 years of age. At the age of 18 years, whole-body fat mass and fat-free mass were determined using dual-energy X-ray absorptiometry. Pubertal development was assessed by the research team between ages 9 and 10 years, and it was recorded annually from the age of 11 years using a validated self-assessment protocol. RESULTS: Catch-up weight gain from birth to the age of 1 year, despite being followed by growth faltering between ages 1 and 2 years, was associated with greater mid-upper arm circumference (P=0.04) and skinfold thickness (P=0.048) at 8 years of age, and with higher weight (P<0.001) and body mass index (P=0.001) at 18 years of age after adjustment for sex, age, smoking during pregnancy, birth order, gestational age, formula-milk feeding and household socio-economic status. Infancy catch-up weight gain was also associated with younger age at menarche in girls (P<0.001). This association persisted after adjustment for smoking during pregnancy, birth order, gestational age, formula-milk feeding and household socio-economic status (P=0.005). CONCLUSION: Transient catch-up weight gain from birth to the age of 1 year among children born in a low-income area of South Africa was associated with earlier menarche and greater adiposity in early adulthood. This observation suggests that modifiable determinants of rapid infancy weight gain may be targeted in order to prevent later obesity and consequences of earlier puberty in girls.

The safety of osteoporosis medication.

Osteoporosis is a common, costly and serious disease, which is still too often regarded as an inevitable part of the normal ageing process and therefore sub-optimally treated, especially in the elderly--in fact, only two out of every 10 patients who sustain a hip fracture receive any form of assessment or prophylactic therapy for osteoporosis. One out of five patients die within 1 year after a hip fracture, and < 50% are capable of leading an independent life. Yet very effective anti-fracture therapy, capable of reducing fracture risk by 35 - 60%, is available. A number of publications have recently questioned the safety of drugs routinely used to treat patients with osteoporosis. This paper attempts to put the situation into perspective and expresses the National Osteoporosis Foundation of South Africa's view on the safety of these drugs. Their efficacy in preventing skeletal fractures and their cost-effectiveness are not addressed in any detail. The paper emphasises the fact that all osteoporosis medications have side-effects, some of which are potentially life-threatening.

Postnatal growth velocity and overweight in early adolescents: a comparison of rural and urban African boys and girls.

OBJECTIVES: To compare growth velocity of two African child cohorts and examine the relationship between postnatal growth velocity in infancy/early childhood and the risk of overweight/stunting in early adolescence. METHODS: The study used data from two child cohorts from urban (Birth to Twenty Cohort, South Africa) and rural (Lungwena Child Survival Study, Malawi) African settings. Mixed effect modelling was used to derive growth and peak growth velocities. T-tests were used to compare growth parameters and velocities between the two cohorts. Linear and logistic regression models were used to determine the relationship between growth velocity and early adolescent (ages 9-11 years) body mass index and odds of being overweight. RESULTS: Children in the BH cohort were significantly taller and heavier than those in the Lungwena cohort, and exhibited faster weight and height growth velocity especially in the first year of life (P < 0.05). No significant association was shown between baseline weight (αw ) and overweight in early adolescence (OR = 1.25, CI = 0.67, 2.34). The weight growth velocity parameter ßw was highly associated with odds of being overweight. Association between overweight in adolescence and weight velocity was stronger in infancy than in early childhood (OR at 3 months = 4.80, CI = 2.49, 9.26; OR at 5 years = 2.39, CI = 1.65, 3.47). CONCLUSION: High weight and height growth velocity in infancy, independent of size at birth, is highly associated with overweight in early adolescence. However, the long term effects of rapid growth in infancy may be dependent on a particular population's socio-economic status and level of urbanization.

The effect of topical calcipotriol or zinc on tuberculin skin tests in hospitalised South African children.

BACKGROUND: The tuberculin skin test (TST) is used to help diagnose tuberculosis (TB) in acutely ill hospitalised children. OBJECTIVE To investigate the potential augmentative effect of topical calcipotriol (a vitamin D analogue) or zinc on TST induration. METHODS: Three TSTs were performed among 64 hospitalised children; each site was covered with topical aqueous cream (control), calcipotriol or zinc and assessed 24 and 48 h later by investigators blinded to all topical applications. RESULTS: TSTs were reactive in 15 (23.4%) children, of whom 13 (20.3%) were TST-positive. Topical calcipotriol and zinc induced TST positivity in two children with reactive but negative control TSTs. These treatments, however, did not significantly increase TST positivity rates. In children with reactive TSTs, the median 48 h induration diameter was not significantly different between the control, calcipotriol- or zinc-treated groups, which were respectively 12.0 (25%-75% IQR 5.0 - 18.0), 14.0 (25%-75% IQR 10.0 - 15.0) and 12.0 (25%-75% IQR 8.0 - 15.0) mm. Topical treatments did not induce TST reactivity or TST positivity in children with culture-confirmed TB disease (n = 4), human immunodeficiency virus infection (n= 18) or kwashiorkor (n = 9). CONCLUSIONS: Topical calcipotriol or zinc does not induce TST reactivity or significantly increase TST positivity rates in acutely ill hospitalised children. However, further studies are required to assess the effects of topical treatments on TST positivity in severely malnourished children.

Pharmacokinetics of daily versus monthly vitamin D3 supplementation in non-lactating women.

This study compared serum cholecalciferol and 25-hydroxyvitamin D (25(OH)D) concentrations over four weeks in healthy, non-pregnant, non-lactating females aged 18-40 years, who were randomized to oral cholecalciferol 5000 international units (IU) daily for 28 days or a single dose of 150 000 IU. The study was conducted in Rochester, MN in March and April of 2010. We found no difference in mean 25(OH)D between treatment groups on study day 0 or day 28 (P=0.14 and 0.28, respectively). The daily group had 11 more days of detectable serum cholecalciferol than the single-dose group (P<0.001). There was no difference observed in cholecalciferol area under the curve (AUC28) between groups (P=0.49). However, the single-dose group had a significantly greater mean 25(OH)D AUC28 compared with the daily group (P<0.001).

Fracture patterns and bone mass in South African adolescent-mother pairs: the Birth to Twenty cohort.

UNLABELLED: The associations of fracture prevalence and bone mass in adolescents with maternal fracture history and bone mass have not been investigated previously in South Africa. Maternal bone mass has a significant inverse association with their adolescents' fracture rates and bone mass across all ethnic groups. INTRODUCTION: Differences in fracture rates and bone mass between families and individuals of different ethnic origins may be due to differing lifestyles and/or genetic backgrounds. This study aimed to assess associations of fracture prevalence and bone mass in adolescents with maternal fracture history and bone mass, and sibling fracture history. METHODS: Data from 1,389 adolescent-biological mother pairs from the Birth to Twenty longitudinal study were obtained. Questionnaires were completed on adolescent fractures until 17/18 years of age and on sibling fractures. Biological mothers completed questionnaires on their own fractures prior to the age of 18 years. Anthropometric and bone mass data on adolescent-biological mother pairs were collected. RESULTS: An adolescent's risk of lifetime fracture decreased with increasing maternal lumbar spine (LS) bone mineral content (BMC; 24 % reduction in fracture risk for every unit increase in maternal LS BMC Z-score) and increased if they were white, male, or had a sibling with a history of fracture. Adolescent height, weight, male gender, maternal bone area and BMC, and white ethnicity were positive predictors of adolescent bone mass. White adolescents and their mothers had a higher fracture prevalence (adolescents 42 %, mothers 31 %) compared to the black (adolescents 20 %, mothers 6 %) and mixed ancestry (adolescents 20 %, mothers 16 %) groups. CONCLUSION: Maternal bone mass has a significant inverse association with their adolescent off-springs' fracture risk and bone mass. Furthermore, there is a strong familial component in fracture patterns among South African adolescents and their siblings.

Bone mass, body composition and vitamin D status of ARV-naïve, urban, black South African women with HIV infection, stratified by CD4 count.

UNLABELLED: This is the first report examining vitamin D status and bone mass in African women with HIV infection using dual-energy X-ray absorptiometry (DXA) with an appropriate HIV-negative control group. Unlike previous publications, it demonstrates no difference in bone mineral density (BMD) or vitamin D status in HIV-positive patients, at different disease stages, vs. HIV-negative subjects. INTRODUCTION: Low bone mass and poor vitamin D status have been reported among HIV-positive patients; suggesting HIV or its treatment may increase the risk of osteoporosis, a particular concern for women in countries with high HIV prevalence such as South Africa. We describe bone mass and vitamin D status in urban premenopausal South African women, who were HIV positive but not on antiretroviral therapy (ARV). METHODS: This study is a cross-sectional measurement of BMD and body composition by DXA and vitamin D status by serum 25-hydroxyvitamin D (25(OH)D) concentration. Subjects were recruited into three groups: HIV negative (n = 98) and HIV positive with preserved CD4 cell count (non-ARV; n = 74) or low CD4 cell counts prior to ARV initiation (pre-ARV; n = 75). RESULTS: The mean (standard deviation (SD)) age of women was 32.1 (7.2) years. Mean CD4 (SD) counts (×10(6)/l) were 412 (91) and 161 (69) in non-ARV and pre-ARV groups (p < 0.0001). Pre-ARV women were significantly lighter and had lower mean BMI than the other two groups (p < 0.002). The pre-ARV group also had significantly less fat and lean mass compared with non-ARV and HIV-negative subjects (p ≤ 0.05). After full adjustment, there were no significant differences in BMD at any site (p > 0.05) between the groups, nor was vitamin D status significantly different between groups (p > 0.05); the mean (SD) cohort 25(OH)D being 60 (18) nmol/l. CONCLUSION: Contrary to previous studies, these HIV-positive women did not have lower BMD or 25(OH)D concentrations than HIV-negative controls, despite the pre-ARV group being lighter with lower BMI.

Association between infant nutrition and anthropometry, and pre-pubertal body composition in urban South African children.

Early life nutrition and growth are related to subsequent obesity risk in high-income countries. We investigated the association between nutrition and growth during infancy, and body composition at 10 years of age in 140 children selected from the Bone Health sub-study of the Birth-to-Twenty cohort from Soweto, Johannesburg, South Africa. Infant feeding and dietary data were collected during the first 12 months, and weight and height were measured at 1 and 2 years of age. At 10 years, anthropometry and dual-energy X-ray absorptiometry (DXA)-derived body composition were measured. Regression models were used to determine associations between independent and dependent variables at the 1% level of significance. A one z-score increase in birth weight was associated with a 1051 g increase in lean mass and a 0.22 increase in body mass index (BMI) z-score at the age of 10 years. After adjusting for confounders, stunting at age 1 year was associated with lower fat mass only at 10 years of age while at age 2 years, it was associated with lower lean mass only. Being underweight at one year of age was significantly associated with lower lean mass only. Weight-for-age (WAZ) change in the second year of infancy was a predictor of fat mass and BMI only. Body fatness at 10 years of age was positively associated with infant WAZ change rather than height-for-age change. There were no significant associations between infant dietary patterns, wasting and being underweight at age 2 years and pre-pubertal body composition. Further studies are needed to assess whether these associations continue during adolescence as pubertal development may be an important modifier of these associations.

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.

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.

How well do waist circumference and body mass index reflect body composition in pre-pubertal children?

OBJECTIVE: To investigate the quantitative relationship between waist circumference (WC) and height (Ht), and subsequently the association between waist circumference index (WCI), body mass index (BMI) and body composition in pre-pubertal children. DESIGN: Cross-sectional sample (n=227; boys=127) of pre-pubertal black children (age range 8.8-11.0 years) from the Bone Health sub-study of the Bt20 birth cohort study set in Soweto-Johannesburg, South Africa. Measures of height, weight and WC by anthropometry, total and truncal fat and lean mass by dual-energy X-ray absorptiometry were used in the analysis. Pearson's correlation coefficients were used to examine the associations between BMI, WC and body composition outcomes. RESULTS: WC was independent of height when height was raised to a power of approximately 0.8. BMI and WCI (WC/Ht) were significantly associated with total and truncal fat and lean mass in both sexes (all P<0.001). BMI showed consistently and significantly higher correlations with body composition than WCI and this association was significantly greater for fat mass than lean mass. CONCLUSION: BMI, rather than WCI, would be a better screening tool for total and truncal fat mass in both sexes before puberty.

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

UNLABELLED: 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.

UNLABELLED: 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.

Socio-economic status and body composition outcomes in urban South African children.

OBJECTIVE: To determine which aspects of socio-economic status (SES) measured at birth and at ages 9 or 10 years, are associated with body composition at ages 9 or 10 years. DESIGN: Mixed longitudinal cohort. SETTING: Johannesburg-Soweto South Africa. PARTICIPANTS: A sub-sample of the Birth to Twenty (Bt20) cohort (n = 281) with data on birth weight, height, weight, fat and lean tissue (whole body dual-energy x ray absorptiometry (DXA)), and birth and ages 9 or 10 years SES measures. MAIN OUTCOME MEASURES: Linear regression was used to estimate the influence of birth and ages 9 or 10 years SES measures on three outcomes: fat mass index (FMI) (fat mass (kg)/height (m)4), lean mass index (LMI) (lean mass (kg)/height (m)2), and body mass index (BMI) at ages 9 or 10 years controlling for sex, age, birth weight and pubertal status. RESULTS: Compared to the lowest SES tertile, being in the highest birth SES tertile was associated with increased LMI at ages 9 or 10 years (beta = 0.43, SE = 0.21 for white and black children and beta = 0.50, SE = 0.23 for black children only), whereas children in the high SES tertile at ages 9 or 10 years had increased FMI (beta = 0.46, SE = 0.22 for white and black children, and beta = 0.65, SE = 0.23 for black children only). SES at birth and at ages 9 or 10 years accounted for 8% and 6% of the variance in FMI and BMI, respectively (black children). CONCLUSIONS: These findings underline the importance of examining SES across childhood ages when assessing nutrition inequalities. Results emphasise the need to consider lean and fat mass as well as BMI when studying SES and body composition in children.