A population-based study of the relationship between salt intake, bone resorption and bone mass

Objective: To explore the relationship between urinary sodium (the best measure of salt intake), urinary calcium, urinary deoxypyridinoline (DPYR) and bone mass. Design: Cross-sectional study. Setting: Population based sample of healthy Hobart residents. Subjects: One hundred and fifty-four (M = 34, F = 120) subjects invited to take part from a systematic sample of the electoral roll and a single newspaper advertisement. Results: In both sexes, urinary sodium correlated moderately with urinary DPYR (r = 0.32, P < 0.0001) and urinary calcium (r = 0.37, P < 0.0001). In multivariate analysis, the combination of urinary sodium, total body bone area, age and sex explained 22% of the variation in log-transformed DPYR (P < 0.00001). In univariate analysis, both urinary sodium and urinary DPYR were strongly associated with bone mineral content and bone mineral density at all sites but this association disappeared after adjustment for confounders particularly body weight. Conclusions: This study has shown that salt intake is associated with markers of bone resorption in a population-based sample of males and females and appears likely to be a risk factor for osteoporosis despite the lack of a demonstrable association between bone mass and a single measure of urinary sodium excretion. Further studies are needed to define the effect of salt intake on bone mass and fractures more clearly. These studies will need to be either longitudinal or interventional in design with repeated measures of urinary sodium so that habitual sodium intake can be accurately assessed and regression dilution bias can be minimised.