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Common blood disorder may be a risk factor for fractures

02 May 2011 European Society of Endocrinology

A common blood disorder, hyponatremia, may be a risk factor for fractures in elderly patients, new research presented at the European Congress of Endocrinology shows.  The study from researchers at Erasmus MC suggests that it may be beneficial to screen elderly patients with fractures for this condition. 

Hyponatremia is a deficiency of sodium in the blood. It most often occurs in elderly subjects and hospitalised patients. Mild hyponatremia usually does not cause any symptoms and is regarded as a benign condition that does not require treatment. Recent studies indicate mild hyponatremia may be linked to an increased risk of fractures, but this has not been demonstrated in a prospective study before.  Fractures in the elderly are most commonly caused by osteoporosis, a condition where bone mineral density is decreased.  This predisposes patients to vertebral fractures (which occur to the backbone and can lead to back pain, immobility and loss of height) and non-vertebral fractures (which involve other bones in the body, most commonly the wrist, upper arm or hip). 

Using data collected in the population-based Rotterdam study, researchers led by Dr Carola Zillikens at Erasmus MC in The Netherlands analysed blood samples from 5208 elderly men and women to assess their levels of sodium.  They also examined how this related to their bone mineral density, recent falls, the number of vertebral and non-vertebral fractures, and mortality over a number of years. 

399 (7.7%) patients had hyponatremia.  Patients with hyponatremia were 40% more likely to experience a non-vertebral fracture during follow-up than non-sufferers (P=0.004).  They were also more likely to have suffered a vertebral fracture at first presentation (P=0.037), but not at follow up. However, hyponatremia was not associated with bone mineral density.  Although people with hyponatremia were significantly more likely to have recently suffered a fall (23.8% vs. 16.4%, P<0.01), this had no effect on their likelihood of experiencing a fracture.  

The results suggest hyponatremia is associated with an increased risk of vertebral and non-vertebral fractures. It is not associated with decreased bone mineral density, as is the case in osteoporosis.  From this, it is unclear whether hyponatremia is a causal factor in the development of fractures or whether it is just an indicator that a patient may be at risk.  As fracture risk in hyponatremia patients was independent of recent falls, this indicates that hyponatremia may be affecting some other aspect of bone quality.  

The researchers now plan to examine the exact relationship between hyponatremia and fracture occurrence and to see if their findings can be replicated in independent populations.  If this is the case, it may be advisable to screen for hyponatremia in elderly patients presenting with fractures. 

Researcher, Dr Carola Zillikens from Erasmus MC said: 

“Osteoporosis and resulting fractures are a huge burden on national health systems and result in decreased quality of life for millions of patients.  Our research shows that patients with hyponatremia are significantly more likely to suffer a fracture than patients without this condition.

“Our next step is to see if these findings can be replicated in independent populations.  If we can do this, it may be advisable to implement a screening programme for hyponatremia in elderly patients that present with fractures. Physicians may consider treatment of mild hyponatremia if future studies show that treatment of mild hyponatremia decreases fracture risk."  

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