Sodium excretion in relation to calcium and hydroxyproline excretion in a healthy Japanese population

Abstract

To evaluate whether habitual excess sodium intake is a significant risk factor for calcium loss, we studied the relation between calcium excretion and sodium excretion in 410 male and 476 female Japanese aged 20-79 y. They were apparently healthy, free-living, and consuming diets of their own choosing. We divided the subjects into two groups: 20-49 y olds and 50-79 y olds. In each group, we observed significant positive correlation between daily calcium excretion and daily sodium excretion in both sexes. Multivariate analyses revealed that in each age group the relation was still significant after sex, age, body weight, and protein, calcium, and phosphorus intakes were adjusted for. The increases in urinary calcium excretion were estimated to be approximately 0.6 and 1.0 mmol for a 100-mmol increment in urinary sodium excretion for the 20-49 y olds and 50-79-y olds, respectively. We also observed significant positive correlations between daily hydroxyproline excretion and daily sodium excretion in both sexes for both age groups. The relation was still significant after sex, age, body weight, and protein intake from meat and fish were adjusted for. The results suggest that individuals with high sodium intake may lose more calcium in their urine than those with low sodium intake.

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

“…This is in agreement with other studies, indicating that there are differences in the metabolic responses to sodium between the young and the elderly (Breslau et al, 1985;Itoh et al, 1999). Although the association between sodium intake and bone resorption in young subjects has been found in several studies (Goulding, 1981;Goulding & Lim, 1983;Chan et al 1992;Itoh & Suyama, 1996;Jones et al, 1997), opposite findings also exist (Castenmiller et al, 1985;Ginty et al, 1998).…”

“…Therefore, it could be postulated that a reduction in salt intake should be of benefit in the prevention of bone loss because it would decrease the urinary excretion of calcium and preserve bone. The correlation of r ¼ 0.45 between urinary sodium/creatinine and calcium/creatinine we found in the beginning of our dietary intervention is at the same level as previously shown in population studies (Goulding, 1981;Law et al, 1988;Itoh & Suyama 1996;Jones et al, 1997). The correlation disappeared by the end of the study, while both calcium intake and excretion remained constant.…”

“…A commonly suggested strategy to diminish bone loss is to maintain positive calcium balance by consuming a diet containing adequate amounts of calcium and vitamin D. The positive relationship between urinary sodium and calcium excretion in humans has been established previously in both cross-sectional (Goulding, 1981;Law et al, 1988;Shortt et al, 1988;Chan et al, 1992;Matkovic et al, 1995;Dawson-Hughes et al, 1996;Itoh & Suyama, 1996;O'Brien et al, 1996;Jones et al, 1997) and experimental studies (Breslau et al, 1982;Goulding & Lim, 1983;Castenmiller et al, 1985;Law et al, 1988;McParland et al, 1989;Zarkadas et al, 1989;Chan et al, 1992;Evans et al, 1997). It could be hypothesised that sodium-induced urinary calcium loss decreases serum calcium concentration, which is compensated for increased excretion of parathyroid hormone (PTH) from the parathyroid glands (Evans et al, 1997).…”

Dietary sodium, an independent determinant for urinary deoxypyridinoline in elderly women. A cross-sectional study on the effect of dietary factors on deoxypyridinoline excretion in 24-h urine specimens from 763 free-living healthy Japanese

“…The ®ndings of our previous cross-sectional studies on a free-living healthy Japanese population consuming diets of their own choosing suggested that individuals with habitual high sodium or protein intake may lose more calcium into their urine than those with low sodium and protein intake (Itoh & Suyama, 1996;Itoh et al, 1998). To evaluate whether this loss of calcium induced by excess intake of sodium or protein from habitual diets is a signi®cant risk factor for bone loss, it is essential to conduct epidemiological studies on the relationship between these dietary factors and bone resorption.…”

“…An expanding body of clinical and epidemiological evidence indicates that increasing calcium intake reduces bone loss and risk of fracture in postmenopausal women (Dawson-Hughes, 1998). Many clinical and epidemiological studies have also con®rmed the calciuric effect of dietary sodium (Shortt & Flynn, 1990;Chan et al, 1992;Itoh & Suyama, 1996) and protein (Linkswiler et al, 1981;Heaney, 1993;Hu et al, 1993;Itoh et al 1998) in healthy subjects. In fact, two longitudinal studies on female subjects indicated negative associations of bone mineral contents with intake of sodium (Devine et al, 1995) or protein (Metz et al, 1993).…”