"Despite a negative correlation (r = −0.31, p < 0.001) between county altitude and the all-cause mortality rate, there was a strong positive correlation (r = 0.50, p < 0.001) between altitude and suicide rate at the county level (Fig. 1)."
Yeah, and that made me wonder whether survivorship bias could be at play. That is, populations at lower elevations see less opportunities for suicide due to individuals dying of things like heart disease, etc., before they have a chance to off themselves at a later age.
But they do mention that they "[controlled] for percent of age >50 yr." Does that imply that, per county, they excluded high-elevation suicides that wouldn't have happened at lower elevations, using known mortality rates for common causes-of-death for age > 50 individuals?
I'm sure the answer is in the paper somewhere, but I need to get back to work. :-)
I'd wager a hidden factor is that slopes are more common in higher altitudes i.e. there are simply more hills and stairs one needs to navigate leading to incidental exercise.
Most population centers in the US west are built on flat land. Think Salt Lake City, Denver, Albuquerque. Even relatively small (80k) Santa Fe, despite having a 5000' elevation gain on its northern edge, is itself almost entirely flat.
"Despite a negative correlation (r = −0.31, p < 0.001) between county altitude and the all-cause mortality rate, there was a strong positive correlation (r = 0.50, p < 0.001) between altitude and suicide rate at the county level (Fig. 1)."