A prospective study of urinary electrolytes and bone turnover in adolescent males

Background & aims The role of excessive salt on bone metabolism in children is uncertain. The aim of this 6-week prospective study was to describe the association between urinary electrolytes and bone turnover markers in a convenience sample of adolescent boys (N=136, mean age 16 yr). Methods Urinary electrolytes (sodium, potassium, calcium and magnesium) were assessed on spot overnight urines on three occasions to minimise regression dilution bias. Bone turnover was assessed by bone specific alkaline phosphatase (BAP) and urinary pyridinoline (PYR) at baseline and follow up. Results In multivariate analysis, urinary sodium (but not other electrolytes) was positively associated with both PYR and BAP both before and after taking short-term growth into account (both p<0.05) and explained 3–6% of the variation in bone turnover markers. Urinary sodium was associated with urinary magnesium (r=+0.26, p<0.05) but only weakly with calcium (r=+0.18, p=0.08). Urinary potassium was significantly associated with urinary magnesium (r=−0.24, p<0.05). Conclusion High urinary sodium (which largely reflects dietary sodium intake in our location) results in a high bone turnover state in adolescent boys which is most likely detrimental for bone. Other urinary electrolytes are not related to bone turnover but may influence bone via other pathways.