Investigation of the Effects of Diet and Exercise on Bone Growth in Young Females.

Abstract

Weight-bearing exercise has been shown to be beneficial for peak bone mass (PBM) development, but whether the skeletal benefits achieved with exercise are maintained if training remains intensive throughout the pubertal years remains undefined. The aim of this research was to investigate the long-term effects of high-impact exercise and the interaction with nutritional factors on PBM development and somatic growth in young females. Longitudinal effects of training on bone metabolism as well as familial influence on growth and development were also examined. At baseline, 45 artistic gymnasts (G) and 52 normally-active controls (C) aged 8-17 years were recruited and followed-up for three years. Anthropometry, diet (repeated estimated dietary records) and physical activity were assessed. Quantitative ultrasound (QUS) measurements were taken. Dual energy x-ray absorptiometry (DXA) scans of total body (TB) and lumbar spine (LS) bone mineral content (BMC) and density (BMD) were taken annually for two years. Blood and urine samples were collected for analysis of bone formation (bone specific alkaline phosphatase, BALP; amino-terminal propeptide of type I procollagen, PINP) and resorption markers (pyridinoline, PYD; deoxypyridinoline, DPD; collagen type I cross-linked C-telopeptide, CTX). To assess heredity influences, 27 G-mothers and 26 C-mothers volunteered for cross-sectional measurements of anthropometry, QUS, BMC/BMD. Compared to the controls, the gymnasts were smaller and lighter (as were their mothers), but had similar growth rates across puberty. Their maturation process occurred later and this was at least partly due to a familial influence. Dietary intakes of energy, macro and micronutrients were found to be sufficient in gymnasts, but only after adjustment for body weight. The gymnasts had significantly higher QUS, axial and appendicular BMC and BMD, with >170 grams more bone mineral in TB across puberty. The main determinants of bone mass were height, weight, maturation, exercise and dietary energy and protein intake. In gymnasts, the biochemical markers of bone turnover which were assessed indicated lower bone resorption in early puberty and higher bone formation in late puberty. These results provide evidence for sustained skeletal benefits from impact-loading exercise throughout the pubertal years, which are unlikely to result entirely from hereditary influences. If the effects are maintained through adulthood into old age, impact-loading exercise during childhood and adolescence may have a valuable role in preventing osteoporotic fractures in later life