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The loss of oxygen from living at high altitudes or with chronic health issues can lead to depression.

A new study from the University of Utah found that female rats living for a week at simulated high altitudes of 10,000 feet, 20,000 feet and 4,500 feet — Salt Lake City's altitude — showed signs of depression. Male rats showed no ill effects.

"The significance of this animal study is that it can isolate hypoxia as a distinct risk factor for depression in those living at altitude (hypobaric hypoxia) or with other chronic hypoxic conditions such as COPD, asthma or smoking, independent of other risk factors," said Shami Kanekar, a research assistant professor of psychiatry at the university and lead author of the report.

In the study published this month in High Altitude Medicine and Biology online, researchers gauged the animals' depression based on their persistence during a swim test.

Because rats do not respond to the same psychological and societal pressures as people, the research strengthens the argument that physiological changes from low oxygen can contribute to depression.

The correlation between high altitude and depression has been documented in previous studies. Work by Perry F. Renshaw, a psychiatry professor at the U. and senior author of the study, suggests high altitude is an independent risk factor for suicide. Depression rates and increased suicide risks may also increase with altitude.

High rates of suicide in the high-altitude Intermountain West — Utah, Colorado, Wyoming, Montana, Idaho, Nevada, Arizona and New Mexico — have led to the region being called the "Suicide Belt."

Researchers believe lack of oxygen may suppress an enzyme that helps make serontonin, a neurotransmitter that boosts feelings of well-being and happiness. And Renshaw's research also has found that the brain's metabolism can be damaged by hypoxia.

Renshaw and Kanekar are studying the effectiveness of currently available antidepressants at high altitude.

"The fact that both depression and suicide rates increase with altitude implies that current antidepressant treatments are not adequate for those suffering from depression at altitude, leading to high levels of unresolved depression that can contribute to higher levels of suicidal ideation and suicide attempts," says Kanekar.

The impact of hypobaric hypoxia on humans will be the subject of future studies.