The joint effect of sodium and potassium on bone health remains uncertain. We examined the associations between urinary excretion of sodium, potassium, and their ratio and bone mineral density (BMD), and reported an inverse association between urinary sodium-to-potassium ratio and BMD in women, but not in men.

Several studies have suggested that a higher sodium or lower potassium intake is associated with poor bone health. However, few studies have examined their joint effects. We examined the associations of urinary excretion of sodium, potassium, and the sodium-to-potassium ratio with BMD in Chinese adults.

This community-based, cross-sectional study included 2202 women and 1063 men (40–75 years) in Guangzhou, China. The BMD of the whole body, lumbar spine, and hip sites were measured by dual-energy x-ray absorptiometry. The concentrations of sodium, potassium, and creatinine of the fasting morning first-void urine sample were measured, and creatinine-adjusted values were then used for further analyses. General information was collected via face-to-face interviews.

For women, after multivariable adjustment, the urinary sodium-to-potassium ratio was inversely associated with BMD at the whole body, total hip, trochanter, and intertrochanter (all p trend <0.05). The mean BMD differences between extreme quartiles ranged from 1.50 to 2.98 % at these sites (all p < 0.05). Similar, but less significant, associations were observed for urinary sodium/creatinine, for which the only significant difference was found at the trochanter (2.00 %, p = 0.016). We did not find any significant associations of BMD with urinary potassium in women and with urinary sodium/creatinine, potassium/creatinine, or their ratio in men.

Our findings suggest that the urinary sodium-to-potassium ratio, but not individual creatinine-adjusted values of sodium or potassium, is a good predictor of BMD in women, but not in men.