TUESDAY, Feb. 3 (HealthDay News) -- Dialysis patients who call higher altitudes home may live longer than patients residing at sea level.
According to a new study from Harvard researchers publishing in the Feb. 4 issue of the Journal of the American Medical Association, patients on dialysis living at elevations upwards of 4,000 feet have a 12 percent to 15 percent lower mortality rate than their lowland counterparts.
This information is immediately valuable in helping scientists untangle the biochemistry of kidney function and raising questions to be answered by future research.
"This information helps us understand what's happening to dialysis patients, their status and long-term outlook," said Dr. Jules Puschett, vice dean for program development at Texas A&M Health Science Center College of Medicine and a nephrologist with Scott & White in Temple, Texas. "We need to verify this with a prospective analysis."
One day, though, this data may translate into therapies that improve mortality even at sea level.
Researchers had previously noted that individuals with end-stage renal disease who lived at higher altitudes paradoxically achieved higher hemoglobin concentrations (hemoglobin is a protein in red blood cells) even while receiving lower doses of erythropoietin, a hormone which stimulates the production of red blood cells.
Possibly, less oxygen available at such elevations leads to more mobilization from the body's iron stores, therefore more efficient production of red blood cells (a process known as erythropoiesis), the researchers hypothesized.
This retrospective study followed more than 800,000 patients in the United States who started dialysis between 1995 and 2004.
After five years of follow-up, the mortality rate was 220.1 per 1,000 person-years at elevations under 250 feet; 221.2 at elevations of 250-1,999 feet; 214.6 between 2000 and 3,999 feet; 184.9 between 4,000 and 5,999 feet; and hit a low at 177.2 at altitudes above 6,000 feet.
That translated into about a 15 percent reduced risk for those at the highest elevations compared to those at the lowest.
Still, it's not entirely clear if the initial hypothesis -- that less oxygen results in more iron and more red blood cells -- explains the outcome.
"So-called hypoxia-inducted factors [factors induced by lower oxygen levels] affect probably more than 100 systems and genes downstream, some of which may affect long-term survival, including those that may affect cardiovascular health," said study author Dr. Wolfgang C. Winkelmayer, an associate physician at Brigham and Women's Hospital and assistant professor of medicine at Harvard Medical School in Boston.
The authors also took the analysis one step further: reviewing data from the U.S. Centers for Disease Control and Prevention to find that the general population also tends to live longer at a higher elevations, though the benefit is less than that seen in dialysis patients.
"This appears to be the first nationwide observation [of an association between altitude and overall mortality in the U.S. population]," said Winkelmayer.
One previous study had indicated that some people living in mile-high or comparable cities get sick from the altitude and tend to move back down.
"This is something we can't take into account [in this study], but if that were truly the case then, if anything, the association in the general population would be attenuated and potentially go away," thereby making the effect in dialysis patients even greater, Winkelmayer said.
The National Kidney Foundation has more on dialysis.
SOURCES: Wolfgang C. Winkelmayer, M.D., Sc.D., associate physician, Brigham and Women's Hospital, and assistant professor, medicine, Harvard Medical School, Boston; Jules Puschett, M.D., senior executive associate dean, program development, professor, medicine, Texas A&M Health Science Center College of Medicine, and nephrologist, Scott & White, Temple, Texas; Feb. 4, 2009, Journal of the American Medical Association