The Nature and Significance of the Relationship between Urinary Sodium and Urinary Calcium in Women

Abstract

Orally or parenterally administered sodium is known to increase urinary calcium in experimental animals and humans, and there is well-documented correlation between urinary sodium and calcium in 24-h urine collections from normal subjects and renal stone formers. The correlation between urinary sodium and calcium is generally sodium driven, i.e., it is the sodium load that influences urinary calcium rather than vice versa, but the converse may also occur, as after an oral calcium load or in hypercalcemia. When sodium is the determinant, 100 mmol of sodium takes out approximately 1 mmol of calcium in the urine. When calcium load is the determinant, each millimole of calcium appearing in the urine is associated with an extra 10-20 mmol of sodium. Sodium-dependent calcium loss may continue indefinitely, but calcium-dependent natriuresis is self-limiting. There is a significant correlation between calcium and sodium in fasting urine from both pre- and postmenopausal women, but there is more calcium relative to sodium in postmenopausal women than in premenopausal women. In postmenopausal but not premenopausal women, urinary hydroxyproline is also related to obligatory sodium and calcium output, and restriction of salt intake lowers not only urinary sodium but also calcium and hydroxyproline. There is not only an increase in obligatory calcium excretion at the menopause, but also an increase in the fasting urinary sodium, which in turn accounts for some of the increase in calcium output. This rise in fasting urinary sodium represents a delay in sodium excretion that may have a significant effect on calcium homeostasis.

A 7-week reduction in salt intake does not contribute to markers of bone metabolism in young healthy subjects

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An Update on the Changing Epidemiology and Metabolic Risk Factors in Pediatric Kidney Stone Disease

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Impacto dos nutrientes na saúde óssea: novas tendências

“…IV -Cloreto de sódio (NaCl) -O NaCl dietético representa prejuízo em potencial para a MO; com aumento da sua ingestão, observa-se elevação da hipercalciúria (43) . A reabsorção renal de Ca é diretamente proporcional à reabsorção de sódio (Na) e, ao elevar-se o NaCl, a reabsorção fracional de Na é diminuída, ocasionando redução paralela na absorção de Ca e prejuízos à MO (44) .…”