People commit suicide for different reasons: mental illness, financial trouble, alcoholism, Blue Monday or even age. But a new study reveals that some people may be committing suicide because of a previously unrecognized factor: They live at high altitudes.

The study, published in the journal High Altitude Medicine & Biology, analyzed cause-of-death data from all contiguous U.S. counties between 1979 and 1998, then broke down the suicide rates in each county. The results were surprising: For counties at high altitudes, the suicide rate was nearly eight times higher than for counties at lower elevations.

Previous studies by the U.S. Centers for Disease Control and Prevention (CDC) had found that suicide rates were higher in the western United States than in other parts of the country. This study's authors, including lead author Dr. Barry Brenner of the University Hospitals Case Medical Center in Cleveland, hypothesized that high elevations might have something to do with it.

The numbers proved his theory out: At elevations between 4,000 and 4,999 feet, county-specific suicide rates jumped to more than double the rate seen at elevations of less than 2,000 feet.

The authors ran the numbers a few ways, mostly to see if the suicides were firearm-related. ("It could be argued that altitude-related suicide may be owing to more firearm usage at higher altitude," the authors wrote.) The rate was still dramatically higher in the mountains.

So what could be causing this higher suicide rate? According to a report from Time Healthland, "The authors note that there may be physiological reasons why high altitude may contribute to suicides; low barometric pressure in mountainous regions, for example, causes the body to become less efficient in transporting oxygen from the air, and these changes can affect brain functioning."

According to the American Foundation for Suicide Prevention, the national suicide rate is about 11.5 per 100,000 people. The rates are much higher in western, mountainous states such as Arizona (16.0), Wyoming (19.3) and Montana (20.5). 

You can read the study in PDF form here.