TUESDAY, Sept. 21 (HealthDay News) -- For years, researchers have observed that U.S. suicide rates appear to be highest among residents of the so-called "Intermountain West" region of the country. Now, fresh research points to a possible explanation: high altitudes.

Other well-observed regional factors, including low population density and the high prevalence of gun ownership, may contribute to the noticeably elevated risk, the study team acknowledged.

But reporting in the Sept. 15 issue of the American Journal of Psychiatry, the researchers say that the metabolic stress that results from the insufficient intake of oxygen -- a common feature of high-altitude living -- could on its own significantly aggravate and contribute to such risk, particularly among people who already struggle with various forms of mood disorders and/or depression.

"There isn't a lot of work that has been done in this area, but asthma and air pollution have been linked in prior research to increased suicide rates around the world," noted study co-author Dr. Perry F. Renshaw, a psychiatry professor at the Utah School of Medicine and an investigator with the Utah Science Technology and Research (USTAR) initiative. "So the physiological environment can play a role in risk. And if there's something about this particular environment that's influencing suicide rates, it's important to know."

According to the study, 20 years of data collected by the U.S. Centers for Disease Control and Prevention (CDC) shows that nine Western states -- Montana, Idaho, Wyoming, Utah, Colorado, Nevada, New Mexico, Arizona, and Oregon -- rank among the top 10 in terms of American suicide rates (with Alaska rounding out the list).

Data gathered from the National Geospatial Intelligence Agency and the National Aeronautics and Space Administration (NASA) also shows that these states have some of the highest elevation levels in the country.

With these numbers in mind, Renshaw and his associates from the University of Utah Brain Institute, the Veteran Affairs Salt Lake City Health System, and Case Western Reserve University also turned to CDC data on gun ownership and population densities in the mountainous west region.

The data revealed that, as expected, suicide rates go up among both gun owners and rural residents.

However, the team concluded that gun ownership and population density alone do not fully explain suicide prevalence, and that even after accounting for these factors, high altitude still appears to be a risk factor for suicide.

For example, Renshaw and his colleagues calculated that those living at an elevation of 6,500 feet above sea level, which is about the average altitude found across Utah, appear to face a one-third higher risk for suicide than those living at sea level.

As a point of comparison, the team's lead author, Namkug Kim, conducted a separate analysis of data on South Korean elevations and suicide rates, finding that people residing at 6,500 feet above sea level in that country also appeared to face a far higher suicide risk, 125 percent greater than those living at sea level.

Nevertheless, the authors cautioned that more research is needed, given the wide range of other factors -- including gender, age, cultural background, ethnicity, family history, and social and economic status -- that figure into the suicide calculus.

"If altitude does play a role, there are probably remedies at hand short of everyone in Salt Lake City moving down to sea level," Renshaw said. "But of course, it's too soon to say what the remedy would be. In fact, if the case we've built for this holds up that will be the 64-million-dollar question."

Alan L. Berman, executive director of the American Association of Suicidology in Washington, D.C., said that while existence of an association between high altitudes and suicide did not surprise him, he felt other more salient factors may be driving the rates seen in the western U.S. region.

"For example, as is well known, these states are generally much more rural than the eastern U.S., where suicide rates are relatively low," he noted. "And in rural and remote areas, there is great distance between a person in psychological trouble and a resource that could intervene: a caregiver, agency, crisis center. Therefore, there is in general going to be less help-seeking and help-receiving."

"Also, white males in particular are at a greater risk for suicide, and these states have low proportions of blacks relative to whites and native Americans, both of which have higher rates of suicide," Berman added.

"So there are a whole number of variables associated with the western or intermountain states where these suicide rates are high," he said. "And those variables may better explain the association than altitude, per se."

More information

For more on suicide risk, visit the National Institute of Mental Health.