Further Experiments on the Calcium Requirement of Adult Man and the Utilization of the Calcium in Milk

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Abstract
Twenty-five calcium balance periods, extending over 12 to 32 days each, were carried out on nine adult men. The first period on each subject involved the testing of diets containing only an average of 203 mg. of calcium daily, but otherwise complete. In subsequent periods the basal diet was supplemented with milk products (liquid whole milk, liquid skim milk, “dried milk solids” and homogenized milk) in amounts to provide enough calcium for approximate equilibrium. Comparisons of the data secured in basal and test periods permitted the estimation, first, of the percentage utilization (biological value) of the supplemental calcium for maintenance, and, second, of the requirement of dietary calcium for equilibrium, i.e., the calcium requirement of maintenance. No evidence was obtained that the calcium in the different milk products studied was utilized with different degrees of efficiency. An average utilization of 29% was observed, although considerable individual variability existed in this respect, the individual averages being, in increasing order, 18, 19, 21, 21, 25, 28, 32, 36 and 49. In particular, it seems clear that the commercial desiccation of milk, or its homogenization, does not appreciably impair the biological utilization of its calcium. The average calcium requirement for equilibrium (maintenance) was 9.55 ± 0.46 mg. daily per kilogram of body weight, or 357 ± 15 mg. per m2 of body surface. This requirement relates to diets in which about two-thirds of the calcium content is provided by milk products. It agrees well with the estimate of Leitch ('36–'37) and that of Mitchell and Curzon ('39), deduced from compilations of published data, but it is 50% higher than the estimate of Sherman ('20). Sherman's estimate of the calcium requirement of maintenance in man is too low by reason of the method of derivation, which neglects to consider the close positive correlation between the intake and the excretion of calcium. The dangers attending the use of any average calcium requirement of maintenance in assessing the prevalence in a community or population of calcium undernutrition are discussed.