High Altitude Living Reduces Risk of Dying Of Ischemic Heart Disease

People living at higher altitudes have a lower chance of dying from ischemic heart disease (IHD) and also tend to have increased longevity, according to a new study.

Researchers at the University of Colorado School of Medicine (UCSM; Denver, USA) and the Harvard School of Global Health (Boston, MA, USA) collected data from the United States National Elevation Dataset, National Center for Health Statistics, and the US Census and analyzed the crude association of mean county altitude with life expectancy and mortality from IHD, stroke, chronic obstructive pulmonary disease (COPD), and cancers. The results were adjusted for associations for socio-demographic factors, migration, average annual solar radiation, and cumulative exposure to smoking in multivariable regressions.

The researchers found that of the top 20 counties with the highest life expectancy in the US, eleven for men and five for women were located in Colorado and Utah; each of these counties was at a mean elevation of 1,800 meters above sea level. Men in these counties lived between 75.8 and 78.2 years, while women ranged from 80.5 to 82.5 years; compared to those living close to sea level, the men lived 1.2-3.6 years longer, and the women 0.5-2.5 years more. Despite this, when socioeconomic factors, solar radiation, smoking, and pulmonary disease were taken into account, the net effect of altitude on overall life expectancy was negligible. The study was published in the March 2011 issue of the Journal of Epidemiology and Community Health.

"If living in a lower oxygen environment such as in our Colorado mountains helps reduce the risk of dying from heart disease, it could help us develop new clinical treatments for those conditions,” said lead author Benjamin Honigman, MD, director of the UCSM Altitude Medicine Clinic. "Lower oxygen levels turn on certain genes and we think those genes may change the way heart muscles function. They may also produce new blood vessels that create new highways for blood flow into the heart.”

The human body can adapt to high altitude through immediate and long-term acclimatization. At high altitude, in the short term, the lack of oxygen is sensed by the carotid bodies, which causes hyperventilation. The hyperventilation, however, also causes respiratory alkalosis, inhibiting the respiratory center. Gradually, the body compensates for the respiratory alkalosis by renal excretion of bicarbonate, allowing adequate respiration to provide oxygen without risking alkalosis. In addition, at high altitude, the heart beats faster; stroke volume is slightly decreased, nonessential body functions are suppressed, and food digestion efficiency declines.

Eventually, the body reaches a new equilibrium, with a lower lactate production, decreased plasma volume, increased hematocrit, increased red blood cell (RBC) mass, a higher concentration of capillaries in skeletal muscle tissue, increased myoglobin, increased mitochondria, increased aerobic enzyme concentration, hypoxic pulmonary vasoconstriction, and right ventricular hypertrophy.

Related Links:
University of Colorado School of Medicine
Harvard School of Global Health