Beneficial effect of physical activity on linear growth rate of adolescents in a South African shanty town

Abstract

It is not known if nutritional and/or other interventions could improve linear growth in adolescents. The purpose of this study was to assess the role of physical activity in promoting linear growth velocity of black adolescents in a low-income shanty town in South Africa. Two schools in a disadvantaged shanty town participated in the study as intervention (n=250) and reference (n=66) groups. Due to practical considerations a quasi-experimental study design was used. Demographic, dietary intake, habitual physical activity and Tanner stage data were collected and anthropometric measurements were carried out over three years. Height for age z-scores (HAZ) were calculated and regression lines were fitted through HAZ values plotted against time. Slopes of HAZ regression lines for each child were used to represent the child's linear growth velocity over the study period. A physical activity intervention was carried out over two years. The main outcome measure, mean growth velocity of children from the intervention versus the reference school was compared using analysis of covariance (ANCOVA), with HAZ at baseline, and habitual physical activity, Tanner stage, and dietary energy, protein, zinc and iron intakes as covariates, and growth velocity (slope of the regression line) as dependent variable. The mean slopes of HAZ regression lines of the intervention (+0.002) and reference groups (-0.007) were significantly different (p=0.009). ANCOVA showed a significantly higher slope of the HAZ regression line in the intervention group than in the reference group [F(1,292)=3.87, p=0.05]. The results indicate a possible role for physical activity in promoting the linear growth of adolescents in low-income areas.