While there are well-known common lifestyle and health factors that contribute to stroke risk, including smoking, high blood pressure, high cholesterol, and lack of physical activity, there is another overlooked factor that could also affect stroke risk – altitude.
Higher altitude means less oxygen availability, to which people living there have adapted. However, how this environment affects someone’s risk for stroke is still unclear. Anecdotal evidence suggests that short-term exposure to low oxygen can contribute to increased blood clotting and stroke risk, but the risk among people who permanently live at high altitude is not clear.
Researchers in Ecuador are in a unique position to explore these phenomena, as the presence of the Ecuadorian Andes means that people in the country live at a wide array of altitudes. Study lead author Esteban Ortiz-Prado, and Professor, Universidad de las Americas, explained:
“The main motivation of our work was to raise awareness of a problem that is very little explored. That is, more than 160 million people live above 2500 metres and there is very little information regarding epidemiological differences in terms of stroke at altitude. We wanted to contribute to new knowledge in this population that is often considered to be the same as the population living at sea level, and from a physiological point of view we are very different.”
The researchers drew on hospital records in Ecuador from between 2001 and 2017, and analysed rates of stroke hospitalisation and mortality among people who live at four different elevation ranges: low altitude (under 1500m), moderate altitude (1500–2500m), high altitude (2500–3500m) and very high altitude (3500–5500m).
Analysis showed that people who lived at higher altitudes (above 2500m) tended to experience stroke at a later age compared with those at lower altitudes. Intriguingly, people who lived at higher altitudes had a lower stroke hospitalisation or mortality risk. This protective effect was greater between 2000 and 3500m, tapering off somewhat above 3500m. In South Africa, Johannesburg sits above 1700m altitude.
One explanation for this finding may be that people who live at high altitude have adapted to the low oxygen conditions, and more readily grow new blood vessels to help overcome stroke-related damage. They may also have a more developed vascular network in their brains that helps them to make the most of the oxygen they take in, but this could also protect them from the worst effects of stroke.
Source: Medical Xpress