People living at high altitudes are less likely to die from coronary heart disease (CHD) and stroke than those living at lower altitudes, research suggests.
The study was conducted in Switzerland, where the populace resides at altitudes ranging between 259 and 1960 meters above sea level. “Our findings not only substantiate the concept of a protective effect of altitude on cardiovascular disease (CV) mortality but also suggest a dose-dependent and sustained effect,” say Matthias Bopp (University of Zürich, Switzerland) and colleagues in the journal Circulation. Geographical disparities in CVD morbidity and mortality have been repeatedly demonstrated, yet little is known about the role of independent environmental factors. One such factor that could influence geographical patterns of CVD mortality and risk factors is altitude. Studies from Peru, Central Asia, and Russia suggest that hypertension is less common at high than at low altitudes, whereas reports from the USA, Italy, and Saudi Arabia showed the opposite. These contradictory findings might be explained by the confounding effects of ethnicity, behavioural risk factors such as smoking and obesity, or access to medical services. Seeing an opportunity to negate these confounders, Bopp et al analyzed census data and death records in Switzerland – a country which has substantial altitudinal variation and universal access to healthcare. To prevent cultural differences influencing the results, the researchers also limited their analysis to the 1.64 million residents who live in the German-speaking region of the country. Bopp and colleagues found that for every 1000-m increase in resident altitude, the rate of mortality due to CHD and stroke decreased significantly by 22% and 12%, respectively. Notably, individuals who were born at high altitudes but had moved to a lower location at the time of the census still appeared to retain the protective effect of high altitude. Discussing their findings, Bopp and colleagues conclude: “Lower mortality at higher altitude did not appear to depend on variations in classic cardiovascular disease risk factors or in sociodemographic characteristics but rather could result from physiological adaptations to altitude or differences in climate (eg, ultraviolet exposure).”
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