High Altitude Is Associated With Lower Stroke-Related Mortality: A 17-Year Nationwide Population-Based Analysis From Ecuador

Abstract Background: Globally, more than 5.7% of the population reside above 1,500 m of elevation. It has been hypothesized that acute short-term hypoxia exposure could increase the risk of developing a stroke. Studies assessing the effect of altitude on stroke have provided conflicting results, some analysis suggest that long-term chronic exposure could be associated with reduced mortality and lower stroke incidence rates. Methods:An ecological analysis of all stroke hospital admissions, mortality rates and disability adjusted life years in Ecuador was performed from 2001-2017. The cases and population at risk were categorized in low (<1,500 m), moderate (1,500-2,500 m), high (2,500-3,500 m) and very high altitude (3,500-5,500 m) according to place of residence. The derived crude and direct standardized age-sex adjusted mortality and hospital admission rates were calculated. Results: A total of 38,201 deaths and 75,893 stroke-related hospital admissions were reported. High-altitude populations (HAP) had lower stroke mortality in men (RR: 0.91 [0.88 - 0.95]) and women (RR: 0.83 [0.79 - 0.86]). In addition, HAP had a significant lower risk of getting admitted to the hospital when compared with the low altitude group in men (RR: 0.55 [CI95% 0.54 - 0.56]) and women (RR: 0.65 [CI95% [0.64 - 0.66]). Conclusions: This is the first epidemiological study that aims to elucidate the association between stroke and altitude using four different elevation ranges. Our findings suggest that living at higher elevations offers a reduction or the risk of dying due to stroke as well as a reduction in the probability of being admitted to the hospital. Nevertheless, this protective factor has the stronger effect between 2,000 m to 3,500 m.