Bone mass and bone size in 10 year-old South African children

Van der Lingen, Linda
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Osteoporosis has been described as a paediatric disease with geriatric consequences. This thesis explored the associations between proximal, historical and predictive genetic and environmental factors affecting bone mass and bone size in socio-economically- and environmentally-disadvantaged black and -advantaged white pre- and early-pubertal South African children. Data were collected from 476 children (182 black boys, 72 white boys, 158 black girls, 64 white girls) of mean age 10.6 years (range: 10.0-10.9), 406 biological mothers and 100 biological fathers. The main findings were that black children and their parents compared to white, had greater DXA-measured BMC at the femoral neck regardless of the way in which BMC was corrected for size (height, weight, BA and/or BAPC) and greater bone strength. Lumbar spine BMC was greater or similar depending on which measures were used to correct BMC for size. At the whole body, mid radius and distal one third of the radius, BMC varied between children, and between their parents, and were dependent on which measures were used to correct BMC for size. Weight at 1 year (WT1), length at 1 year (LT1) and birth weight (BW), were significant predictors of BMC of the femoral neck (P<0.05-0.01) after correcting BA and BMC for race/ethnicity, gender, age, socioeconomic status, bone age, height and weight at 10 years. Maternal and paternal heritability was estimated to each be ~30% in both black and white subjects. The main conclusion was that ethnicity is the single most important proximal factor affecting bone mass and bone size in 10 year old South African children. Black children demonstrate a superior bone mass and bone strength at the femoral neck. Historical and predictive factors however indicate that black children have not been programmed for optimal bone health in utero and early life, nor are contemporary environmental factors favourable for the maximisation of peak bone mass. This cohort may be at risk of developing osteoporosis as an elderly population, particularly at the lumbar spine and forearm.
Thesis (Ph.D.)--University of the Witwatersrand, Faculty of Health Sciences, 2012