THE EFFECT OF DIETARY-SODIUM INTAKE ON BIOCHEMICAL MARKERS OF BONE METABOLISM IN YOUNG-WOMEN

To investigate the effect of a low (80 mmol/d) or high (180 mmol/d) Na intake for 14d on biochemical markers of bone turnover in Na-sensitiv e and Na-non-sensitive healthy young women, twenty-nine subjects were screened for responsiveness of urinary Ca excretion to increasing diet ary Na intake (40, 80, 120 and 200 mmol/d for 7d). Ina crossover study , the eight Na-sensitive and eight of the twenty-one Na-non-sensitive subjects were randomly assigned to diets containing either 80 or 180 m mol Na/d for 14 d followed by crossover to the alternative diet for a further 14 d. Dietary Ca was restricted to 12.5 mmol/d throughout. Dur ing each dietary period, fasting morning first void urine samples (las t 3 d) and fasting blood serum samples (morning of twelfth day) were c ollected. Increasing Na intake from 80 to 180 mmol/d increased urinary Na about twofold in both the Na-sensitive and Na-non-sensitive groups and increased urinary Ca excretion (by 73 %) in the Na-sensitive grou p only. Biochemical markers of bone resorption (urinary pyridinoline a nd deoxypyridinoline) and bone formation (serum osteocalcin and bone-s pecific alkaline phosphatase; EC 3.1.3.1) were unaffected by increasin g dietary Na in either group. It is concluded that the Na-induced calc iuria observed in the Na-sensitive healthy young women did not result in increased bone resorption or turnover and, despite restricted Ca in take, adaptation of dietary Ca absorption may have compensated for the increased urinary Ca loss.