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-sensitive and Na-non-sensitive healthy young women, twenty-nine subjects were screened for responsiveness of urinary Ca excretion to increasing dietary 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 mmol 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. During each dietary period, fasting morning first void urine samples (last 3 d) and fasting blood serum samples (morning of twelfth day) were collected. 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 group only. Biochemical markers of bone resorption (urinary pyridinoline and deoxypyridinoline) and bone formation (serum osteocalcin and bone-specific alkaline phosphatase; EC 3.1.3.1) were unaffected by increasing dietary Na in either group. It is concluded that the Na-induced calciuria observed in the Na-sensitive healthy young women did not result in increased bone resorption or turnover and, despite restricted Ca intake, adaptation of dietary Ca absorption may have compensated for the increased urinary Ca loss.