Sodium excretion influences calcium homeostasis in elderly men and women

This study was conducted to compare associations between urinary sodium and calcium in elderly men and women, overall and by level of calcium intake, and to examine associations between urinary sodium excretion and bone mineral density in the same population. Healthy men (n = 249) and women (n = 665) over age 65 y had measurements of 24-h urinary sodium and calcium and spine, hip, and whole-body bone mineral density. Urinary sodium and calcium excretion were significantly correlated in men (r = 0.42, P = 0.0001) and women (r = 0.26, P = 0.0001), but the regression coefficient was greater in men than in women (beta = 0.017 vs. 0.010, P = 0.007). Within each gender, associations between 24-h urinary sodium and calcium were similar and significant at intermediate and high calcium intakes but were not significant at very low intake levels. Urinary sodium was not correlated with bone mineral density. In conclusion, in healthy elderly men and women, urinary sodium and calcium excretion are linked at moderate and high dietary calcium intakes but not at low calcium intakes. For a given sodium excretion, elderly men excrete more calcium than women.