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

Association of low-sodium salt intervention with osteoporosis: A cross-sectional study based on the SSaSS study

Low-sodium salt has a protective effect on BMD and also reduces the risk of osteopenia due to elevated blood glucose. This provides a direct and effective way to improve bone health in patients with hyperglycemia.

OBJECTIVE

There is no consensus on the relationship between salt type and bone mineral density (BMD). This study examined the factors affecting osteoporosis and the relationship between low-sodium salt consumption with osteoporosis based on the Substitute Salt and Stroke Study (SSaSS).

METHODS

This study was a cross-sectional study and compares the prevalence and characteristics of osteoporosis and osteopenia. Multiple linear regression and restricted spline models were used to analyze the factors affecting BMD and its dose-response relationship with osteoporosis and to compare the effects of different salts.

RESULTS

The rates of osteoporosis and osteopenia were lower in those consuming low-sodium salt (31.11% and 38.52%) than in those consuming normal salt (38.65% and 41.10%). BMD was higher in the population consuming low-sodium salt than in that using normal salt (= 0.64, 95%CI: 0.25, 0.97). Age, gender, and blood glucose level interacted with low-sodium salt and together affected BMD. Analysis of the dose-response relationship revealed a positive linear association between elevated blood glucose and the risk of osteopenia (P for overall < 0.05, P for nonlinear = 0.77), but intake of low-sodium salt significantly reduced this risk. The risk of OP increased with age (P for overall < 0.05, P for nonlinear = 0.72); low-sodium salt intake reduced this risk, with the effect being more pronounced among individuals < 70 years old.

CONCLUSION

Low-sodium salt has a positive effect on maintaining BMD. Elevated blood glucose and age < 70 years increase the risk of osteoporosis, but use of low-sodium salt mitigates this risk.

Urinary Mineral Concentrations in European Pre-Adolescent Children and Their Association with Calcaneal Bone Quantitative Ultrasound Measurements

This study investigates differences and associations between urinary mineral concentrations and calcaneal bone measures assessed by quantitative ultrasonography (QUS) in 4322 children (3.1–11.9 years, 50.6% boys) from seven European countries. Urinary mineral concentrations and calcaneal QUS parameters differed significantly across countries. Clustering revealed a lower stiffness index (SI) in children with low and medium urinary mineral concentrations, and a higher SI in children with high urinary mineral concentrations. Urinary sodium (uNa) was positively correlated with urinary calcium (uCa), and was positively associated with broadband ultrasound attenuation and SI after adjustment for age, sex and fat-free mass. Urinary potassium (uK) was negatively correlated with uCa but positively associated with speed of sound after adjustment. No association was found between uCa and QUS parameters after adjustment, but when additionally adjusting for uNa, uCa was negatively associated with SI. Our findings suggest that urinary mineral concentrations are associated with calcaneal QUS parameters and may therefore implicate bone properties. These findings should be confirmed in longitudinal studies that include the food intake and repeated measurement of urinary mineral concentrations to better estimate usual intake and minimize bias.

The influence of dietary sodium on bone development in growing rats

The present study investigated the effects of dietary sodium on bone growth in young rats. Five-week-old rats were fed one of three different diets for 60 days: low sodium (NaCl, 0.32 g/kg diet), normal sodium (NaCl, 2.6 g/kg) and high sodium (NaCl, 20 g/kg). The proximal tibial metaphysis (PTM), the fifth lumbar vertebra (LV5) and the middle part of the tibia shaft (TX) were analysed by bone histomorphometry. The expression of three osteogenesis genes, Runx2, osteopontin and osteocalcin, was determined by RT-PCR in bone samples from the skull. In both the PTM and LV5, trabecular area and thickness were increased by the low-sodium diet, while the high-sodium diet decreased trabecular area in LV5. Dynamic data revealed that sodium restriction increased bone formation parameters in the PTM and LV5, but decreased bone resorption in LV5. In TX, endosteal bone formation was enhanced by the low-sodium diet and depressed by the high-sodium diet compared to the normal sodium group. But there were no statistically changes in the cortical bone area of TX. Low-sodium intake significantly enhanced the expression of all three osteogenesis genes compared to the normal sodium group, while high-sodium intake suppressed osteogenic gene expression. Our results suggest that sodium restriction in growing rats promotes bone development by influencing both bone formation and resorption.

Higher urinary sodium, a proxy for intake, is associated with increased calcium excretion and lower hip bone density in healthy young women with lower calcium intakes

We assessed 24-h urinary sodium (Na) and its relationship with urinary calcium (Ca) and areal bone mineral density (aBMD) at the whole body, lumbar spine and total hip in a cross-sectional study. 102 healthy non-obese women completed timed 24-h urine collections which were analyzed for Na and Ca. Dietary intakes were estimated using a validated food frequency questionnaire. Participants were grouped as those with lower vs. higher calcium intake by median split (506 mg/1000 kcal). Dietary Na intake correlated with 24-h urinary loss. Urinary Na correlated positively with urinary Ca for all participants (r = 0.29, p < 0.01) and among those with lower (r = 0.37, p < 0.01) but not higher calcium intakes (r = 0.19, p = 0.19). Urinary Na was inversely associated with hip aBMD for all participants (r = -0.21, p = 0.04) and among women with lower (r = -0.36, p < 0.01) but not higher (r = -0.05, p = 0.71) calcium intakes. Urinary Na also entered a regression equation for hip aBMD in women with lower Ca intakes, contributing 5.9% to explained variance. In conclusion, 24-h urinary Na (a proxy for intake) is associated with higher urinary Ca loss in young women and may affect aBMD, particularly in those with lower calcium intakes.

Higher habitual sodium intake is not detrimental for bones in older women with adequate calcium intake

Based on the calciuric effect of sodium (Na), it has been speculated, although not proven, that higher Na intake might have a detrimental effect on bone health. The objective was to determine the relationship between Na intake (expressed as urinary Na) and bone mineral density/content (BMD/BMC) during a 3-year study. Participants were healthy, postmenopausal, Caucasian women (n = 136 at baseline) with no medications affecting bone. After baseline screening, half were instructed to reduce sodium intake to approximately 1,500 mg/day (intervention). The other half remained on habitual intake of approximately 3,000 mg/day (control). All subjects were given calcium and vitamin D supplements to achieve recommended levels. Anthropometries, densitometry, blood and 24-h urine analyses, and dietary and activity records were assessed every 6 months. Data were analyzed as a continuum, irrespective of the initial assignment to a control or intervention group, using random effects regressions with repeated measures analysis of variance to examine changes over time. Results showed that subjects with higher Na intake had higher BMD in the forearm and spine at baseline and all subsequent time-points (p < 0.01). In the forearm, time and higher urinary calcium modified results, producing a curvilinear decrease in BMD (p < 0.01). In the spine, more active individuals had higher BMD at all time-points. We conclude that higher sodium intake, within the range consumed, had a positive effect on some skeletal sites and no adverse effect on bone in women who had adequate calcium and vitamin D intake.

Sodium and bone health: impact of moderately high and low salt intakes on calcium metabolism in postmenopausal women

High salt intake is a well-recognized risk factor for osteoporosis because it induces calciuria, but the effects of salt on calcium metabolism and the potential impact on bone health in postmenopausal women have not been fully characterized. This study investigated adaptive mechanisms in response to changes in salt and calcium intake in postmenopausal women. Eleven women completed a randomized cross-over trial consisting of four successive 5-wk periods of controlled dietary intervention, each separated by a minimum 4-wk washout. Moderately low and high calcium (518 versus 1284 mg) and salt (3.9 versus 11.2 g) diets, reflecting lower and upper intakes in postmenopausal women consuming a Western-style diet, were provided. Stable isotope labeling techniques were used to measure calcium absorption and excretion, compartmental modeling was undertaken to estimate bone calcium balance, and biomarkers of bone formation and resorption were measured in blood and urine. Moderately high salt intake (11.2 g/d) elicited a significant increase in urinary calcium excretion (p = 0.0008) and significantly affected bone calcium balance with the high calcium diet (p = 0.024). Efficiency of calcium absorption was higher after a period of moderately low calcium intake (p < 0.05) but was unaffected by salt intake. Salt was responsible for a significant change in bone calcium balance, from positive to negative, when consumed as part of a high calcium diet, but with a low calcium intake, the bone calcium balance was negative on both high and low salt diets.

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.