ASSOCIATIONS OF PHYSICAL-ACTIVITY AND CALCIUM INTAKE WITH BONE MASS AND SIZE IN HEALTHY WOMEN AT DIFFERENT AGES

Weight-bearing exercise and calcium intake are known to contribute to bone density. However, the relative significance of physical activity and calcium intake in the development of bone characteristics in funct ionally different weight-bearing and nonweight-bearing bone sites at d ifferent ages is poorly known. A total of 422 women in three age group s (25-30, 40-45, and 60-65 years) were screened from 1017 women and di vided into four groups by their level of physical activity (high [PA()] and low [PA(-)]) and calcium intake (high [Ca+] and low [CA(-))]. T otal body bone mineral content (TBBMC), areal bone mineral density (BM D) of the femoral neck and distal radius, and selected dimensions and estimated strength variables (bone width, cortical wall thickness, cro ss-sectional moment of inertia, and section modulus of the femoral and radial shafts) were measured with dual-energy X-ray absorptiometry. B oth high physical activity and high calcium intake were associated wit h a higher TBBMC when compared with low activity and calcium intake (1 .8% and 4.6%, respectively). The BMD of the weight-bearing femoral nec k was 5% higher in the PA(+) groups than in the PA-groups, whereas cal cium intake showed no such significant association. Neither physical a ctivity nor calcium intake was associated with the BMD of the nonweigh t-bearing radius. However, both high physical activity and high calciu m intake were related to larger and mechanically more competent bones in the femoral and radial shafts, the association for physical activit y being stronger with increasing age. No significant interaction betwe en physical activity and calcium intake was found with respect to any of the bone variables. These data from a cross-sectional study suggest that a moderate level of physical activity or a sufficient level of c alcium intake, if maintained from childhood, can result in considerabl e long-term improvement in the mechanical competence of the skeleton. The clinical relevance of these findings is further emphasized by the fact that the observed patterns of physical activity and calcium intak e pertain to customary lifestyle and are thus feasible targets for the primary prevention of osteoporosis.