Nutrient intake among a longitudinal group of urban black South African children at four interceptions between 1995 and 2000 (Birth-to-Ten Study)

Assessment of the Dietary Intake of Schoolchildren in South Africa: 15 Years after the First National Study

There has not been a national dietary study in children in South Africa since 1999. Fortification of flour and maize meal became mandatory in October 2003 to address micronutrient deficiencies found in the national study in 1999. The purpose of this review was to identify studies done after 1999 in schoolchildren, 6–15 years old, in order to determine whether dietary intakes reflected improvements in micronutrients, namely: iron, zinc, vitamin A, folate, thiamine, riboflavin, vitamin B6, and niacin. An electronic and hand search was done to identify all studies complying with relevant inclusion criteria. The search yielded 10 studies. Overall, there is a paucity of dietary studies which have included the fortified nutrients; only four, of which only one, reported on all micronutrients; making it difficult to determine whether fortification has improved the micronutrient intake of schoolchildren. This is further complicated by the fact that different dietary methods were used and that studies were only done in three of the nine provinces and thus are not generalizable. The results of these studies clearly point to the importance of doing a national study on the dietary intake of schoolchildren in order to confirm the outcomes of the fortification process.

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.

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.

Variety and total number of food items recorded by a true longitudinal group of urban black South African children at five interceptions between 1995 and 2003: the Birth-to-Twenty (Bt20) Study

OBJECTIVE

To report on the variety and total number of food items recorded by a true longitudinal group of urban black South African children (n = 143) from the Birth-to-Twenty Study at five interceptions at the ages of 5 (1995), 7 (1997), 9 (1999), 10 (2000) and 13 (2003) years, respectively.

METHODS

Dietary intake was assessed using a semi-quantitative food-frequency questionnaire. Frequencies were calculated per week, for each interception and for all five interceptions combined, using SAS.

RESULTS

Five hundred and forty-six different individual food items were recorded 23 480 times for all five interceptions combined. The highest of 124 items was recorded in 1999 contributing 23% of the 546 items recorded. Each of the top 10 items (rice, stiff maize-meal porridge, chicken, sugar, sweets, tea, eggs, full-cream milk, carbonated beverages and oil) contributed between 2.5% and 3% and these items were recorded almost 600 times or more for all interceptions combined (n = 23 840). Rice and stiff maize-meal porridge were the top items recorded 684 and 676 times, both contributing 2.87% and 2.84%, respectively. The variety of food items and the ratio of the food groups to the total number of foods recorded in the present study were not significantly different but the denominators decreased over the five interceptions.

CONCLUSION

The variety of food items recorded did not vary between 1995 and 2003 - the fact that new items were not added to the questionnaire as the children grew older could have contributed to this phenomenon. However, there was a difference in the ranking of these items that may suggest a change in eating patterns.

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.

Energy, macro- and micronutrient intake among a true longitudinal group of South African adolescents at two interceptions (2000 and 2003): the Birth-to-Twenty (Bt20) Study

OBJECTIVE

This study reports on the energy, macro- and micronutrient intakes of a true longitudinal group of 143 urban black South African children from the Birth-to-Twenty (Bt20) study at two interceptions (2000 and 2003) when they were 10 and 13 years old, respectively.

METHODS

Subjects resided in the urban Johannesburg/Soweto area of the Gauteng Province in South Africa. Dietary intake was assessed using a semi-quantitative food-frequency questionnaire. The coded data were analysed using SAS.

RESULTS

Mean daily intake of energy, all six macronutrients and most micronutrients (17/19) increased from 2000 to 2003. Of the 19 micronutrients investigated, the mean daily intake of eight (calcium, iron, zinc, vitamin A, riboflavin, nicotinic acid, pantothenic acid and biotin) fell below the recommended dietary allowance (RDA) at both interceptions. More than 70% of the children consumed less than the RDA for these same eight nutrients. From 2000 to 2003, there was a decrease in the percentage of children falling below the RDA for energy (from 73 to 59%), but an increase in the percentage of children falling below the RDA for most of the micronutrients. There was a positive percentage change in mean daily intake for all 26 macro- and micronutrients from 2000 to 2003.

CONCLUSION

Mean daily intake of nutrients increased from 2000 to 2003, but intakes for most micronutrients were still below the RDA at both interceptions for a large percentage of the children. The study has provided valuable information on the nutrient intake and change in intake over time among a longitudinal group of South African adolescents.

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.

Estudos de consumo alimentar: aspectos metodológicos gerais e o seu emprego na avaliação de crianças e adolescentes

Este artigo discute aspectos metodológicos dos estudos de consumo alimentar em crianças e adolescentes. Para compreender esses aspectos, descreve, em contexto mais amplo, a importância da Epidemiologia Nutricional no estudo descritivo da relação da dieta com o surgimento das enfermidades, bem como origem histórica, importância, vantagens, limitações e usos dos métodos empregados para medir a ingestão alimentar, especialmente em crianças e adolescentes, em estudos epidemiológicos populacionais. Apresenta ainda alguns trabalhos da literatura científica clássica e contemporânea, demonstrando os resultados obtidos e algumas sugestões para aperfeiçoamento desses métodos. Finalmente, evidencia os aspectos mais relevantes que, por consenso de vários pesquisadores, competem como fatores limitantes ou facilitadores no emprego desses métodos, conferindo a esses, maior validade e reprodutibilidade nos estudos de consumo alimentar de crianças e adolescentes.