FACTORS INFLUENCING THE URINARY EXCRETION OF CALCIUM. I. IN NORMAL PERSONS1

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Abstract
Through the study of the urinary Ca excretion of 606 normal persons, from 1 to 80yrs. of age, under standard dietary regulation, the normal range of urinary excretion of Ca was established. The quantity of urinary Ca is dependent on an endogenous factor or factors, presumably endocrine, and on Ca intake/unit of wt. Age and sex are not factors except as they affect skeletal wt. It is thus possible to compare data from subjects of all ages and with varying dietary intakes. Uri- nary Ca expressed as % of Ca intake varies inversely with the intake/kg., and is an exponential function of the latter. Values for mean, minimum, and maximum normal urinary Ca may be expressed by equations. The urinary Ca excretion of subjects below 2 yrs. of age is within the normal range but below the mean value for older children and adults. Dietary factors other than Ca intake have relatively minor effects on urinary Ca, with the exception of ingested acids, ketogenic diets, or diets with a high Ca to P ratio, all of which increase urinary Ca, often above maximum normal limits. The ability to demarcate the normal range of urinary Ca with accuracy should aid in further studies of Ca metabolism, as well as in diagnosis of disease entities associated with alteration of urinary excretion of Ca.