The association of environmental and lifestyle factors with bone mass acquisition in South African children by sex, race and age
Year: 2009
Type: dissertation
Study design: Observational Study
Abstract: While osteoporosis is a major public health concern in the developed world, little research \nregarding factors influencing bone mineral accrual in children has been conducted in \ndeveloping countries. South Africa is of particular interest since the incidence of hip fractures \nin South African Blacks has been reported to be amongst the lowest in the world (32; 253). In \nthis thesis, the association of lifestyle factors; in particular physical activity (PA), socio \neconomic status (SES) and dietary calcium intakes on the growing skeleton of Black and \nWhite South African children is investigated. \nAfter using accelerometry to validate a physical activity questionnaire (PAQ), in a \nconvenience sample of South African Black, White, male and female children (n=30), fitness \nlevels were assessed in a larger group (n=69) of similarly aged children, stratified by race and \ngender. Fittest subjects had significantly greater physical activity scores (p=0.022) as reported \non the PAQ, lower body mass index’s (BMI) (p=0.001) and least percentage body fat \n(p=0.001) (as assessed using Dual Energy X-ray Absorptiometry (DXA), than least fit \nsubjects. White males who reported to be significantly more active than all other groups on \nthe PAQ were significantly fitter (p<0.001) than White females and Black males and females. \nThe next study sought to determine whether differences observed in physical activity levels \nbetween groups showed an association with bone mineral content (BMC), density (BMD) and \narea (BA) (as assessed using DXA). PA was analyzed in terms of a metabolic (METPA; \nweighted metabolic score of intensity, frequency, and duration) and a mechanical (MECHPA;sum of all ground reaction forces multiplied by duration) component for 386 children aged 9.5 \n(0.04) years recruited from a longitudinal birth cohort study. White children expended a \nsignificantly greater energy score (METPA of 21.7 (2.9)) than Black children (METPA of 9.5 \n(0.5), p< 0.001). When children were divided into quartiles according to the amount and \nintensity of sport played, the most active White children had significantly higher (p<0.05) \nwhole body BMD and higher hip and spine BMC and BMD after adjustment for body size \nthan less active children. White children in the highest MECHPA quartile also showed \nsignificantly higher (p<0.05) whole body, hip, and spine BMC and BMD after adjustment for \nbody size than those children in the lowest quartile. No association between PA and bone \nmass of Black children was found. No significant differences between METPA and \nMECHPA quartiles and BA were observed for any group. \nGiven the disparate backgrounds from which many South African children come, the next \nstudy sought to determine whether differences in socio-economic status between Black and \nWhite South African children influence PA patterns. This study explored the relationship \nbetween socio-economic status, PA anthropometric and body composition (via DXA) \nvariables in 381 children aged (9.5 (0.04) years) recruited from a longitudinal birth cohort \nstudy . Children falling into the highest socio-economic status quartile had mothers with the \nhighest educational levels, generally came from dual parent homes, were most physically \nactive, watched less television, weighed more and had greater lean tissue than children in \nlower socio-economic quartiles (p<0.001). Significantly greater levels of lean mass (p<0.001) \nwith increased activity level were observed after controlling for television watching time and \nfat mass. There were high levels of low physical activity and high television watching time \namong lower socio-economic status groups. White children were found to be more active than \nBlack children, more likely to be offered physical education and to participate in physical \neducation classes at school and watched less television than Black children. \nThe final study sought to investigate the association between habitual PA patterns and dietary \ncalcium intakes with bone mass acquisition over a one year period in 321 pre-pubertal South \nAfrican children recruited from a longitudinal birth cohort study. Data were analyzed by \nregressing change in BMC and BA from age nine to ten years, against BA (for BMC), height and body weight. The residuals were saved and called residualized BMCGAIN and BAGAIN. \nResidualized values provide a good indication of weight, height and BA-matched \naccumulation rates. White children had significantly higher PA levels and calcium intakes \nthan Black children. Most active White males had significantly higher residualized \nBMCGAIN and BAGAIN at the whole body, hip and spine but not at the radius, than those \nwho were less active. Most active White females had significantly higher residualized \nBAGAIN at all sites except the radius than less-active girls. No such effects were seen in \nBlack children. There was no interactive effect on residualized BMCGAIN or BAGAIN for \ncalcium intake and PA in boys or Black girls, but an interactive and possible synergistic effect \nof calcium and physical activity was observed at the spine, radius and hip in White girls. In \nthis population, PA has an osteogenic association with White children, but not Black children, \nwhich may be explained by the lower levels of PA in the Black children. Despite this, Black \nchildren had significantly greater bone mass at the hip and spine (girls only) (p< 0.001) even \nafter adjustment for body size.In conclusion, differences between White and Black children’s PA levels were observed, with \nWhite children reporting higher PA levels and exhibiting higher fitness levels than Black \nchildren. Physical fitness correlated well with self reported physical activity levels on the \nPAQ and objectively measured body composition. Socio-economic status differences between \nWhite and Black children are highly related to differences in physical activity patterns and \nbody composition profiles. Bone mass and area gain is accentuated in pre- and early-pubertal \nchildren with highest levels of habitual physical activity. Limited evidence of an effect of \ndietary calcium intakes on bone mass in boys and Black girls was found. The role of exercise \nin increasing bone mass may become increasingly critical as a protective mechanism against \nosteoporosis in both South African race groups, especially because the genetic benefit \nexhibited by Black children to higher bone mass may be weakened with time, as \nenvironmental influences become stronger.
Author: Joanne A. McVeigh
Language: English
Subfield: Orthopedics and Sports Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2236094842