Physiological Aspects of Aging

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Abstract
Mice representing 3 adult ages (7, 21 and 26 months) were subjected to a low-calcium, low-magnesium diet for a period of 10 days to determine their relative capacities to adapt to a reduced intake of these elements. Whereas the youngest group attained calcium equilibrium during this period, the older animals were in significant negative balance which was attributable to an increased loss of endogenous calcium from the skeleton. The net digestibility coefficients for dietary calcium, determined by the isotope dilution method, were similar for the 3 groups. An analogous age effect was observed with respect to magnesium balance. The results indicate that the capacity for calcium absorption is unimpaired in aged mice, but that following a reduction in calcium intake old animals are more susceptible to a negative calcium balance as a result of an accelerated rate of skeletal catabolism.