Dialysis patients who live at high altitudes have a significantly reduced risk of mortality, according to a study published in Hemodialysis International.
Kamyar Kalantar-Zadeh, MD, MPH, PhD, of the University of California Irvine Medical Center and colleagues studied a national cohort of 144,892 dialysis patients with a follow-up of 801 days to examine the connection between residential altitude and all-cause mortality in these patients.
All patients had stage 5 chronic kidney disease and were undergoing dialysis treatment from July 2001 to June 2006. The investigators compiled data from the U.S. Geological Survey to link residential zip codes with patient information.
In fully-adjusted analysis, the researchers found that high residential altitude, defined as 6000 feet or greater, was associated with a significant 8% reduction in all-cause mortality risk in dialysis patients compared with living at less than 250 feet.
“These results support previous findings, although the effect size we observed was smaller in comparison,” the authors noted.
Patients living in higher altitudes were more likely to be white, married, on peritoneal dialysis, and receiving catheter dialysis access, compared to those on lower altitudes (less than 250 feet). They also displayed higher hemoglobin and creatinine levels, but lower parathyroid hormone levels.
Previous studies have attributed improved survival of dialysis patients at high altitude to the regulatory effects of hypoxia-induced factors on enzymes associated with cardiovascular risk, according to Dr. Kalantar-Zadeh and his colleagues. The researchers also suggested a possible role for ultraviolet B (UV-B) radiation exposure, which increases 15% for each 1,000 meter rise in elevation. UV-B is important for production of vitamin D, which has been associated with improved cardiovascular risk and all-cause mortality in incident dialysis patients and health populations, they pointed out.
“Further studies are needed to confirm our findings and to more clearly delineate the pathways by which high altitude confers a reduction in mortality risk,” they concluded.