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June 17, 2009

Association Between Altitude and Mortality in Incident Dialysis Patients

JAMA. 2009;301(23):2442-2443. doi:10.1001/jama.2009.842

To the Editor: In their cohort analysis of incident dialysis patients, Dr Winkelmayer and colleagues1 speculated that the inverse association observed between altitude and all-cause mortality in both dialysis patients and the general US population may be due to hypoxia-induced regulation of enzymes to reduce cardiovascular risk.

Another possible explanation of their findings is that populations living at high altitudes have higher vitamin D levels, which reduces their risk of cardiovascular disease compared with those living at sea level.2 UV-B radiation, which is the primary source of vitamin D in humans, increases with altitude by about 15% per 1000 m because of decreasing ozone.2 Moreover, the photoconversion of 7-dehydrocholesterol to previtamin D3 has been shown to increase with altitude, particularly above 2000 m.3

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