The Calcium Content of the Normal Growing Body at a Given Age

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Abstract
Normal animals at a given age were compared (males and females separately) as to whether the percentage of body calcium differed materially with the body weight of the animal; i.e., with the rate at which it had grown. Such comparisons were made independently with animals from three different diets representing successive levels of liberality of calcium intake. Thus there were six comparisons, each embracing from sixty-four to eighty animals. In none of these six comparisons did the larger animals show a higher percentage of body calcium than the smaller animals of the same age, as would be the case if the higher body weight meant greater maturity of skeletal development at the age studied (28 days in the rat, or “end of infancy”). Obviously the amount (total weight) of calcium in the body tends to vary with its size. The comparisons which follow are therefore made on the basis of percentage of body calcium. In all of the six comparisons, the smaller animals show a slightly higher, and the larger animals a slightly lower, percentage of body calcium than the general average of their group. The differences, however, were only such as might be regarded as being near the limit of accuracy of the method of experiment and analysis, and so on the border line of possible statistical significance. Thus the rate of growth as expressed by the body weight at a given age, is in itself not a disturbing factor in the rate of calcification involved in normal development. This finding is of special significance in the interpretation of certain investigations upon the influence of food. These analyses of well over 400 experimental animals establish the fact that among normal growing individuals of a given sex, having the same hereditary and nutritional background, age is the predominant determining factor in the increasing percentage of calcium in the body.