DIETARY-PROTEIN INTAKE AND URINARY-EXCRETION OF CALCIUM - A CROSS-SECTIONAL STUDY IN A HEALTHY JAPANESE POPULATION

To evaluate whether habitual excess protein intake is a significant ri sk factor for calcium loss, we studied the relation between urinary ex cretion of calcium and protein intakes, in 349 male and 406 female Jap anese aged 20-79 y. The subjects were apparently healthy, free-living, and consuming diets of their own choosing. We divided the subjects in to two groups: those aged 20-49 y and those aged 50-79 y. In each grou p, we observed a significant positive correlation between daily urinar y excretion of calcium and protein intake. Calcium excretion also corr elated positively with daily urinary excretion of urea. Multivariate a nalyses revealed that in each age group the relation between calcium e xcretion and urea excretion remained significant even after sex, age, body weight, urinary sodium excretion, and calcium intake were adjuste d for. The correlation of calcium excretion with animal protein intake was significantly positive in both sexes and in each age group wherea s that with plant protein was not. We observed a significant positive correlation between daily calcium excretion and daily urinary excretio n of sulfate. The correlation in 50-79-y old subjects remained signifi cant even after sex, age, body weight, sodium excretion, and calcium i ntake were adjusted for. Our findings suggest that excess protein, esp ecially that rich in sulfur-containing amino acids, in habitual diets may augment calcium excretion in the urine, at least in the elderly.