Correlations are everywhere, and not all of them are meaningful. Here I'll point out a short open access paper, in PDF format only at the moment, that outlines an interesting relationship between population altitude, mortality rate, and incidence of common age-related conditions. In short, people at higher altitudes have modestly better long term health and a few years of additional life expectancy when compared with those closer to sea level - a fairly interesting outcome, and one that might spur speculation. It has to be said that there are a number of fairly straightforward relationships between location and longevity. In many cases these are fairly obviously connected to wealth. If you look at wealthier regions, you find people who benefit from that wealth: greater access to medical technology and information about health, the education and will to use those resources, and all of the other matters of status, intelligence, and so forth that are linked with wealth in a web of correlations. If you look at smaller wealthier locations, you find selection and migration effects in which those already tending to greater longevity due to their greater wealth move there.
In the case of altitude, however, wealth isn't an obvious factor, one that might be used to explain greater health and longevity at higher elevations. The authors of this paper reach instead for greater levels of exercise as a likely factor, which is reasonable given the geography of the regions under study. Exercise and diet have two of the largest effects when it comes to natural variations in health and longevity, so thinking about how to use them to explain this sort of data is usually the best approach. As always, bear in mind that I point out papers of this nature because the subject is interesting, not because it is of any practical use whatsoever. Small variations of a few years up or down are unimportant, and the gains you can obtain from exercise and calorie restriction are only worth chasing because they cost nothing but time and the expected outcome is both reliable and backed by a large amount of scientific evidence, which is more than can be said for anything else you can do right now, this instant. The future of longevity for all of us is overwhelmingly determined by progress in medical science, the construction of rejuvenation therapies capable of repairing and reversing the causes of aging. The more of that taking place, the better off we are and the longer we live in good health. Even first generation therapies should extend human life to a much greater degree than just the few years of difference noted in this paper.
Individuals living at moderate altitudes (up to about 2000m) were shown to have lower mortality from coronary artery disease (CAD) and stroke (-22% and -12% per 1000m) and an about 50% lower risk of dying from Alzheimer's disease compared with their counterparts living at lower altitudes. In contrast, reported altitude effects on cancer mortality are still conflicting. However, due to shared risk factors, e.g. obesity and diabetes, in cardiovascular disease and cancer a shared biology for both disease entities may be assumed. Therefore, it is hypothesized that mortality from certain cancers will decline with increasing altitude as demonstrated for CAD. Altitude-dependent mortality from CAD, male colorectal cancer and female breast cancer from 2003 to 2012 in Austria has been evaluated based on data from the Austrian Mortality Registries (Statistik Austria). Since the phenomenon of migration was most pronounced towards larger communities (a population of greater than 20,000) only communities with a population below 20,000 were included to avoid important confounding from migration.
The general life expectancy, e.g. in 2009, increased from low altitude (less than 251m) to higher altitudes (1001 to about 2000m) by about 2 years, in males from 76.7 to 79.1 years and in females from 82.1 to 84.1 years. From low to higher altitudes, mortality rate from CAD decreased by 28% in males and by 31% in females. Mortality rate from male colorectal cancer and female breast cancer decreased almost linearly from low to higher altitude by 45% and 38%. Independent of altitude, increasing agriculture employment was associated with a diminished mortality from ischemic heart disease by about 15% for males and females. In contrast, solely increasing altitude was related to the reduction in cancer mortality.
The lower mortality from CAD at moderate altitudes is in close agreement with that reported from Switzerland. Reduced oxygenation at higher altitudes and altitude-related climate changes, e.g. temperature, UV radiation, and/or air-pollution but also differences in dietary behaviour were considered as potentially protective factors. Similarly, a set of altitude-dependent environmental and life-style factors have been suggested to contribute to lower mortality from Alzheimer's disease at higher altitudes. The present data extend preventive effects of living at higher elevations on male colorectal and female breast cancer mortality. The observation that more rural conditions may not have affected cancer mortality will even heighten the importance of altitude-specific effects. The nearly linear mortality reduction with increasing altitude strongly indicates a dose-response relationship.
Unfortunately, to date only little and conflicting information is available on cancer mortality at altitude. Given the fact of shared risk factors in cardiovascular disease and cancer the beneficial effects of moderate hypoxia stimuli at altitudes up to 2500m on cardiovascular risk factors might also contribute to the lowering of cancer mortality. For instance, obesity and diabetes are such shared risk factors which have recently been reported to be lower in US individuals living at higher altitudes. These authors speculated that cold-induced thermogenesis, decreased appetite, unintentional increased physical activity, and hypoxia-related better glucose tolerance could represent potential mechanisms explaining the inverse relationship between the prevalence of obesity and/or diabetes and altitude. The author of an ecological study attributed lower cancer death rates at higher places to elevated natural background radiation (hormesis theory) but emphasized that causal inferences cannot be made.
Besides changing climate conditions with increasing altitude a potentially higher exercise capacity in the altitude population helps to explain lower mortality. Whereas high-altitude regions like Leadville in Colorado (US) or the Altiplano in South America are rather flat, in the Alps the amount of hilly terrain increases steeply with altitude likely contributing to a higher fitness level in the altitude population. In the Swiss study a similar amount of physical activity in the low and higher altitude populations has been suggested. However, since the hilly terrain is much more challenging than the plain terrain, e.g. when walking or cycling, a similar amount of physical outdoor activities can result in higher exercise capacity in the altitude population. In any case, the remarkable protective effects of living at moderate altitudes also on cancer mortality are fascinating and deserve further investigation.