Researchers speculate that the benefit is related to factors induced by hypoxia.

Patients who initiate dialysis at high altitude may be at lower death risk compared with those start treatment at low altitude, such as near sea level, according to researchers.

The finding comes from a study of 804,812 patients with end-stage renal disease (ESRD) who initiated dialysis between 1995 and 2004. The investigators, led by Wolfgang C. Winkelmayer, MD, ScD, of Harvard Medical School in Boston, stratified subjects by the average elevation of their residential zip code. Subjects had a median follow-up of 1.78 years.

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As altitude increased, death from any cause decreased, the researchers reported in the Journal of the American Medical Association (2009;301:508-512). Compared with patients initiating dialysis at an altitude below 76 meters, those starting dialysis at an altitude higher than 1,828 meters had a 15% reduced mortality risk after controlling for demographic characteristics, comorbid conditions and other potential confounders.

“The magnitude of this observation was markedly greater than the observed small reduction in mortality at higher altitude in the general population,” the authors wrote. “We propose that hypoxia-inducible factors are persistent at high altitude in patients with ESRD and may confer protective effects.”

The authors cited a recent study published in the Journal of the American Society of Nephrology (2008;19:1389-1395) showing that ESRD patients living at higher altitudes achieved greater hemoglobin concentrations while receiving lower doses of erythropoietin.

Dr. Winkelmayer’s group hypothesized that such an observation could be explained by greater activation of hypoxia-inducible factors, which may boost erythropoietin efficacy and iron availability. Moreover, they noted that hypoxia-induced factors regulate enzymes that could affect cardiovascular risk, such as vascular endothelial growth factor, heme-oxygenase-1, inducible nitric oxide synthase, and cyclooxygenase 2.