Long-term effects of activity and of calcium and phosphorus intake on bones and kidneys of female rats.

Over a 22-week period, young female rats in conventional cages gained significantly more weight than rats housed with free access to running wheels. A trend toward increased bone density was indicated in runners. In a second test, young female rats were housed under the same conditions for 30 weeks, but the active group was then forced to run in a treadmill for 30 minutes, 5 times a week, over a 43-week period. During this time rats were fed either diets providing adequate Ca (0.5%) and adequate P (0.4%) or high P (1.2%), or low Ca (0.3%) and high P (1.2%). Running appeared to benefit long bone density but could not completely compensate for a high P or a low Ca, high P intake. A bone that received only indirect stress during exercise (atlas) was not significantly affected by running. However, a high P diet significantly decreased atlas bone density, while the negative effect of this diet on the density of long bones was at a lower level of significance. A low Ca, high P diet clearly decreased bone density in all bones investigated. Running had no effect on kidney mineralization, but either a high P or low Ca, high P diet greatly increased the concentration of these minerals in the kidney.