Effect of salt restriction on urine hydroxyproline excretion in postmenopausal women

Fasting calcium and hydroxyproline excretion are related to fasting sodium excretion in postmenopausal women. We postulate that calcium excretion is sodium dependent and that hydroxyproline excretion is calcium dependent. Therefore, we sought to lower urinary hydroxyproline, which is a marker of bone resorption, by lowering urinary sodium. Fasting urine samples were obtained from 59 postmenopausal women before and after 2 to 7 days of dietary salt restriction. The urinary sodium-to-creatinine ratio fell from 16 to 7; calcium to creatinine, 0.30 to 0.26; and hydroxyproline to creatinine, 18.2 to 16.8. In the 28 subjects with starting sodium-to-creatinine ratios greater than 15, the hydroxyproline-to-creatinine ratio fell from 19.6 to 16.3. Salt restriction may be one way of reducing bone resorption in postmenopausal women, particularly in those whose sodium intake is high.