Sodium excretion in relation to calcium and hydroxyproline excretion in a healthy Japanese population

To evaluate whether habitual excess sodium intake is a significant risk factor for calcium loss, we studied the relation between calcium excretion and sodium excretion in 410 male and 476 female Japanese aged 20-79 y. They were apparently healthy, free-living, and consuming diets of their own choosing. We divided the subjects into two groups: 20-49 y olds and 50-79 y olds. In each group, we observed significant positive correlation between daily calcium excretion and daily sodium excretion in both sexes. Multivariate analyses revealed that in each age group the relation was still significant after sex, age, body weight, and protein, calcium, and phosphorus intakes were adjusted for. The increases in urinary calcium excretion were estimated to be approximately 0.6 and 1.0 mmol for a 100-mmol increment in urinary sodium excretion for the 20-49 y olds and 50-79-y olds, respectively. We also observed significant positive correlations between daily hydroxyproline excretion and daily sodium excretion in both sexes for both age groups. The relation was still significant after sex, age, body weight, and protein intake from meat and fish were adjusted for. The results suggest that individuals with high sodium intake may lose more calcium in their urine than those with low sodium intake.