Endocrine Abstracts (2011) 26 OC3.1

Mild hyponatremia as a risk factor for fractures: the Rotterdam study

E J Hoorn, F Rivadeneira, J B J van Meurs, G Ziere, B H Ch Stricker, Albert Hofman, Huibert Pols, R Zietse, A G Uitterlinden & M C Zillikens

Erasmus MC, Rotterdam, The Netherlands.

Introduction: Recent studies suggest that mild hyponatremia is associated with fractures, but prospective studies are lacking.

Aim: Our aim was to study whether hyponatremia is associated with fractures, falls and/or bone mineral density (BMD).

Methods: Five thousand two hundred and eight elderly men and women with serum sodium assessed at baseline were included from the prospective, population-based Rotterdam Study. The following data were analyzed: BMD, vertebral fractures (at baseline and after mean follow-up of 6.4 years), non-vertebral fractures (mean follow-up of 7.4 years), recent falling, co-morbidity, medication, and mortality.

Results: Hyponatremia was detected in 399 subjects (7.7%, 133.4±2.0 mmol/l). Subjects with hyponatremia were older (73.5±10.3 vs 70.0±9.0 years, P<0.001), had more recent falls (23.8 vs 16.4%, P<0.01), higher type 2 diabetes mellitus prevalence (22.2 vs 10.3%, P<0.001), and more often used diuretics (31.1 vs 15.0%, P<0.001). Hyponatremia was not associated with BMD, but was associated with increased risk of incident non-vertebral fractures (HR=1.39, 95% CI 1.11–1.73, P=0.004) after adjustment for age, sex and body mass index. Further adjustments for disability index, use of diuretics or psycholeptics, recent falls and prevalent diabetes did not modify results. Subjects with hyponatremia also had increased risk of vertebral fractures at baseline (OR=1.78, 95% CI 1.04–3.06, P=0.037) but not at follow-up, after adjustment for all covariates. Finally, all-cause mortality was higher in subjects with hyponatremia (HR=1.21, 95% CI 1.03–1.43, P=0.022).

Conclusion: Mild hyponatremia in the elderly is associated with increased risk of prevalent vertebral fractures and incident non-vertebral fractures but not with BMD. Increased fracture risk in hyponatremia was also independent of recent falls, pointing towards a possible effect on bone quality. When our findings are replicated in an independent population, screening for hyponatremia should be advised for elderly patients with fractures.

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