DIETARY-SODIUM AND BONE-MINERAL DENSITY - RESULTS OF A 16-YEAR FOLLOW-UP-STUDY

BACKGROUND AND PURPOSE: It has been proposed that high dietary sodium intake, resulting in a sodium-mediated increase in renal calcium excre tion, is a risk factor for osteoporosis. To evaluate the relationship between dietary sodium intake and bone mineral density (BMD), a prospe ctive study of the Rancho Bernardo cohort was performed. METHOD: A 24- hour diet recall was done for the period 1973 through 1975; follow-up bone mineral density of the ultradistal radius, midradius, total hip, and spine was measured between 1988 and 1991. Covariates were ascertai ned by self-report and examination at baseline. Multivariable analysis of the sodium-BMD association was performed using gender and menopaus e-specific linear regressions. RESULTS: All subjects were white. At th e bone evaluation, there were 258 women (average age 73.3 years) and 1 69 men (average age 72.4 years). In both men and women, higher levels of sodium intake were strongly associated with higher levels of calciu m intake and total calories. Body mass index increased with sodium qua rtile in women, while a modest negative association was seen in men. I n women, after age adjustment, positive associations between dietary s odium and bone density were found at the ultradistal radius (beta = 0. 01, P = 0.03) and the total hip (beta = 0.019, P = 0.02). BMD increase d by 0.01 to 0.02 g/cm(2) per gram increase in sodium ingested. After adjustment for estrogen use, body mass, dietary calcium, alcohol, and total calories, these effects were no longer significant. Similar patt erns were seen in pre- and postmenopausal women. In men, age and multi variate-adjusted BMD increased with higher sodium intake at the ultrad istal radius only (beta = 0.013, P = 0.05). Stratification by gender-s pecific median calcium level did not significantly effect the results. CONCLUSIONS: After control for confounders, a small, statistically si gnificant protective effect of sodium was found at the ultradistal rad ius in men only. At other sites in women and men, no effect of sodium on BMD was apparent in the multivariable models. These results do not support a detrimental effect of dietary sodium on bone mineral density . Rather, the findings suggest that sodium intake, in the range measur ed, is not a major osteoporosis risk factor.