The state of Utah is known for three things: its incredible outdoor activities, its religious significance and — incongruously — its high suicide rate.

Utah's windswept sandstone arches, powder-packed peaks and Great Salt Lake serve as a year-round mecca for outdoor adventure enthusiasts, and Utah residents know how to take advantage. The state has the shortest average workweek in the country, suggesting this group knows how to find the right work/life balance.

So it has baffled researchers for years that despite ranking as America's happiest state, Utah is also tops in anti-depressant use. And the state has disproportionately high rates for both mood disorders and suicide. According to the Centers for Disease Control and Prevention, Utah and other states in the Rockies consistently have the highest suicide rates in the country aside from Alaska.

A number of possible theories have circulated over the years to explain this puzzle including gun use, low population density and the state's strong Mormon influence. But one neuroscientist thinks there's another explanation for what he calls the "Utah paradox": altitude.

Perry Renshaw, a neuroscientist at the University of Utah, first noticed a connection between altitude and depression when he moved to Utah in 2008. Renshaw believes that altitude has an impact on brain chemistry, specifically that it changes the levels of serotonin and dopamine, two key chemicals in the brain that help regulate our feelings of happiness. 

In a 2010 study published in High Altitude Medicine and Biology, researchers looked at suicide rates across 2,584 counties in 16 states and found that those rates increase with elevation, specifically between 2,000 and 3,000 feet, and not just in the U.S. Analysis of suicide rates in other countries, including South Korea and Austria, produced similar results.

Another study collaborated these findings. In a 2011 study published in the American Journal of Psychiatry, Renshaw and a team of researchers analyzed state suicide rates and factors such as gun ownership, poverty, health insurance and availability of psychiatric care. Of all the factors, Renshaw found that the one with the strongest link to suicide was altitude. 

So what would altitude have to do with suicide risk? Renshaw believes that the answer is in the air. As altitude increases, the air gets "thinner;" in other words, it becomes less oxygen-rich. Diminished oxygen changes brain chemistry, causing both a drop in serotonin and an increase in dopamine. Serotonin and dopamine are brain chemicals that influence mood — too little serotonin leads to depression while too much dopamine leads to feelings of euphoria.

Still, not everyone agrees with Renshaw's altitude-based suicide theory. Many point to anecdotal evidence of native Utahans who move away from home only to feel depression and a longing to return to the mountains. But Renshaw thinks it's each individual's DNA that determines which way oxygen deprivation will go. That would explain why some folks feel that "Rocky Mountain high" while others struggle with depression and anxiety. 

And he also notes that it's probably only one piece of the puzzle. In fact there are likely multiple factors that determine a person's suicide risk. But Renshaw argues that the effects of altitude should not be ignored as a possible cause.  

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