Bone Growth During Puberty and the Effects of Exercise and Calcium on Bone Mass Accrual

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URL: https://vuir.vu.edu.au/id/eprint/15610

Abstract

Childhood and adolescence are time periods characterised by the rapid growth and development of the skeletal system. The timing and magnitude of skeletal development varies considerably between individuals however, environmental factors may make significant contributions to the variance in bone mass. To optimise the development of bone it is important to identify and promote factors that may have a positive effect on bone mass accmal. Two lifestyle factors that may enhance bone mass accmal are calcium and exercise. The focus of this thesis was to investigate bone mass accmal in children and adolescents and to determine the effect calcium and exercise have on bone mass accmal. The research involved three studies. The first study compared calcium intakes in older (aged 13-18 yrs) and younger (aged 8-12 yrs) boys and girls, and to determine if calcium intakes demonsttated seasonal variations. The findings from this study revealed that older girls consumed significantly less calcium (and calcium from fluid milk) than younger girls (951 mg.day⁻¹ v 1021 mg.day⁻¹, p < 0.01). In contrast, older boys reported greater calcium intakes than younger boys (1386 mg.day⁻¹ v 1179 mg.day⁻¹, p < 0.001). Seasonal variations in calcium intake were reported for younger girls, who consumed less calcium (1001 mg.day⁻¹ v 1076 mg.day⁻¹, p < 0.05) and calcium from fluid milk (501 mg.day⁻¹ v 568 mg.day⁻¹, p < 0.05) in winter compared to summer. The second study compared peak height and tissue velocities in early versus late maturing boys and girls. The findings from this study revealed that males reached peak height and tissue velocities significantly later than females (mean difference 1.5 years, p < 0.001) and demonstrated significantly greater magnitudes at peak (p < 0.001). The age of peak height velocity (PHV) was negatively correlated with the magnitude of PHV in both sexes (r = -0.4, p < 0.05). Late maturing males had accmed more bone mineral (1779 g v 1493 g, p < 0.05) and lean mass (41.8 kg v 36.6 kg, p < 0.05), and were taller (168.1 cm v 161.6 cm, p < 0.05) by the age of PHV in comparison to early maturers. The third study determined the effects of 8.5 months of high impact exercise and calcium supplementation on bone mass accmal in pre-and early-pubescent girls. The findings from this study revealed that calcium supplementation enhanced bone mass accrual in the arms (13.6% v 10.4%, p < 0.05 relative to placebo), and high impact exercise enhanced bone mass accmal predominantly at the legs (16.7% v 14.4%, p < 0.05 relative to low impact exercise). A combined effect of exercise and calcium was reported at the femur. No effects of either calcium or exercise were detected at the lumbar spine. The results from these studies highlight the need for adequate calcium and weight bearing exercise during growth to enhance bone mass accrual. In spite of this, many children, in particular older girls in general and younger girls in winter are not consuming sufficient calcium. The effect of these variations in calcium intake on bone mineral content is yet to be determined. The enhanced need for calcium during periods of rapid skeletal growth, as reflected by the elevated recommended calcium intake levels during adolescence, may vary both between and within the sexes due to the variations in the timing and magnitude of these skeletal events. In conclusion the promotion of an adequate calcium intake and weight bearing exercise in this young population may serve to enhance bone mass accmal to optimise skeletal integrity.

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