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15-03-2011 | Bone health | Article

Low sodium linked to fracture risk in elderly

Abstract

Free abstract

MedWire News: Elderly men and women with mild hyponatremia have an increased risk for sustaining non-vertebral fractures, relative to those with normal serum sodium levels, results from The Rotterdam Study show.

Carola Zillikens (Erasmus Medical Center, Rotterdam, The Netherlands) and colleagues report that the increased fracture risk was not explained by increased comorbidity, the use of diuretics, or a history of recent falling, and may therefore be caused by currently undetermined effects of hyponatremia on bone quality.

Severe complications of hyponatremia have long been recognized and include cerebral edema and osmotic demyelination, whereas mild chronic hyponatremia has traditionally been regarded as benign, says the team.

However, mild hyponatremia has recently been associated with fractures. To investigate this association in a prospective cohort, Zillikens et al analyzed data for 5208 participants (61.5% women) of The Rotterdam Study for whom data on serum sodium was present at baseline.

They looked at the possible relationships between hyponatremia - defined as a serum sodium level below 136 mmol/l - bone mineral density (BMD), falls, and fractures.

At baseline, 339 (7.7%) participants had hyponatremia, at a mean level of 133.4 mmol/l. The remaining participants were classed as normonatremic.

Hyponatremic participants were, on average, 3.5 years older than their normonatremic counterparts, at 73.5 versus 70.0 years.

The hyponatremic group also had significantly more recent (within 12 months) falls at baseline (23.8% vs16.4%), higher diabetes prevalence (22.2% vs 10.3%), and more often used diuretics (31.1% vs 15.0%) than the normonatremic group.

In addition, the rate of non-vertebral fracture during 7.4 years of follow-up was significantly higher in the hyponatremic versus the normonatremic group (23.3% vs 17.3%), whereas vertebral fractures during a 6.4-year follow-up period did not differ between the groups (5.9% vs 5.4%, respectively).

Multivariate analysis showed that hyponatremia was not associated with reduced BMD, but was significantly associated with a 34% increased risk for incident non-vertebral fractures compared with normonatremia, independent of age, gender, body mass index, comorbidity, diuretic use, fall history, and diabetes.

After adjusting for the same factors, hyponatremia was also associated with an increased risk for prevalent (at baseline) but not incident vertebral fractures (odds ratio=1.78).

"Mild hyponatremia is a new and important risk factor for fractures in the elderly," conclude Zillikens and co-authors in the Journal of Bone and Mineral Research.

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2011

By Laura Dean

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