THE EFFECTS OF PHYSICAL ACTIVITY, CALCIUM INTAKE AND SELECTED LIFESTYLE FACTORS ON BONE DENSITY IN YOUNG WOMEN

Abstract

Achievement of maximum bone density in early adulthood may be the key to preventing skeletal fragility in the elderly. The purpose of this study was to investigate lifestyle and dietary factors that may relate to bone density in young women. The study involved two primary components. The first was a cross-sectional examination of the relationship of selected lifestyle factors and dietary calcium to bone density in an experimental population of 101 young women, aged 20 to 35 years. The second was to investigate the effects of six months of physical activity and calcium diet supplementation (separately and combined) on bone density in the same population. Seventy­ eight women completed the six-month experimental trial. Os calcis bone density, the dependent variable measured in both components of the study, was determined using the GE 9800 CT scanner at the University Hospital, Saskatoon. Three to five contiguous CT images, each 3 rom in thickness, were computed for the right os calcis of each subject and the image representing the most central region of the bone was used for data analysis. There appeared to be no relationship between height, weight or age and bone density in the cross-sectional analysis. Childhood physical activity was a key determinant of bone density in the study sample. Those subjects who participated in organized sport or fitness activities as children had significantly higher bone density than those who did not (�(99)=2.00, £<.05). The classification of childhood physical activity within a four category criteria (Sometimes Active, Active, More Active, Very Active) also identified significant differences in adult bone density (1(3,97)=2.74, £<.05). Childhood milk consumption, current calcium intake and current lifestyle factors (e.g. cigarette smoking, coffee consumption avocational physical activity), considered separately, did not appear to be significant determinants of bone density in early adulthood. When cigarette smoking and current coffee consumption were considered together, there was a significant difference in bone density between non-smoking subjects with low daily coffee intake compared to subjects who smoked cigarettes daily and consumed five or more cups of coffee per day (�(55)=1.99, £<.05). The results of the six-month experimental trial indicated that most young women, aged 20 to 35 years have not begun to suffer an age-related loss of trabecular bone and may have the potential to increase trabecular bone density. Sixty-three of the 78 subjects (80.8%) in the experimental trial maintained or gained bone density within the trabecular region of the os calcis over the six month duration of the study. Over a six-month treatment period, calcium supplementation and exercise intervention (separately and combined) failed to generate a significant osteogenic effect in the experimental population.