Alterations in calcium intake on peak bone mass in the female rat

This study compared the effect of a calcium deficit or surfeit on bone growth and development in the early phase of peak bone mass attainment with the late phase of peak bone mass attainment using the female Sprague-Dawley rat as a model. Groups of weanling animals were fed one of three nutritionally complete but calcium-altered diets (0.25%, 0.5%, or 1.0% calcium) for 8 weeks. Animals within each diet group were then rerandomized into one of the above diets and fed until 37 weeks of age. Each group contained five rats. In addition, three groups that received the 0.25% calcium diet for the first 8 weeks remained on the diet until week 20 when they were further randomized into one of the three diet groups and fed until 37 weeks of age. Results of this experiment indicate that increasing the calcium intake after adolescence (12-weeks-old) of those female rats consuming a low calcium diet will not substantially alter the adult bone volume of the metaphyseal region of the proximal tibia. Further, low calcium intakes through adolescence retard and prolong longitudinal bone growth. In contrast, however, those rats fed a diet providing calcium either at (0.5%) or twice the National Research Council's requirement level through adolescence had greater tibial bone volume as an adult when fed diets containing 1.0% calcium after this time period. It appears that the mechanism for this increase involves both a protection from resorption and an increase in bone formation/mineralization. This study is the first to show that low calcium intakes through adolescence have a nonreversible, deleterious effect on peak bone mass, whereas higher intakes promote greater peak bone mass and provide potential protection from age-related bone loss.