Some call it the Las Vegas threshold. It’s the sensation, when you drive out of Vegas down I-15 toward the Pacific, of becoming happier, lighter. Dr. Perry Renshaw attributes this phenomenon to how high you got in Vegas. But not like that. Vegas sits at 2,000 feet above sea level, and Ren­shaw, who studies the effects of altitude on emotional well-being, thinks that’s the exact elevation where a person’s mood starts to shift.

It’s long been established that the states that span the Intermountain West, from Montana to New Mexico, have the greatest suicide rates in the country. According to the Centers for Disease Control and Prevention, someone who lives in Wyoming is five times more likely to take his own life than someone who lives in Washington, D.C. Researchers who study depression call the region the Suicide Belt.

Renshaw’s research draws on the experiences of people like Mark Matthews. When Matthews moved from Maui to Taos, New Mexico, he immediately noticed a change. He traveled a lot for work, and every time he returned to the Sangre de Cristo Mountains — elevation 7,000 feet — he felt immense dread. “I’d come home, and a couple of days later, everything would get heavy,” he tells me. “It was full-on depression, and there were no triggers, so I started to think, Could it be the elevation? It was the one factor that I couldn’t account for.”

A neurobiologist who focuses on brain chemistry in patients with psychiatric disorders, Renshaw moved from Boston to Salt Lake City in 2008 to teach at the University of Utah. Shortly after he arrived, he attended a talk by a suicidologist. “He showed this amazing map of how suicide rates differ across the country, and the Rocky Mountain states lit up,” says Renshaw, who now runs a 15-person lab within the university’s psychiatry department. Fifty-six years old, he has a hyperfocused gaze, and his speech still retains a no-nonsense East Coast cadence. “The thinking at that time was on gun ownerships and the rural nature of those states, but to me, getting off the plane and hyperven­ti­lating, I thought it could be something else.”

In Boston, Renshaw had studied how energy creation within the brain differed in people with mood disorders, and he wondered if the lower partial pressure at altitude could affect the creation of serotonin, the neuro­transmitter that moderates mood and anxiety, and dopamine, the neuro­transmitter associated with risk­-taking behavior and adrenaline. To make sure his conjecture wasn’t bunk, he set up a statistical regression to see how altitude correlated with suicide and with other known suicidal triggers. Of the nearly 20 factors he looked into, ranging from divorce rate to income to education level, altitude was the second most significant indicator of suicide risk.

After Renshaw’s first paper was published in 2009, studies in South Korea, Spain, and Austria came to similar conclusions: Altitude and suicide rates tracked together, even in countries where the mountain cultures are significantly different from one another. Other research confirmed that mood can deteriorate quickly when you climb. A recent study by the Office of Naval Research found that after 30 days at altitude, Marines who had previously shown no signs of mental distress displayed levels of anger and fatigue that mimicked adult male psychiatric outpatients.



Renshaw’s lab recently tested the theory using rats. A researcher kept animals at four different altitudes and then put them through a forced swim test, a standard measure for depression. Rats were dropped into steep-sided tanks, and those that had been exposed to a higher elevation stopped swimming much sooner than those who had been at sea level, an indicator of unhappiness. (The rats were plucked out of the pools before they drowned.)

The findings have met some re­sistance among mental-health researchers. Part of the skepticism stems from the truism that correlation isn’t causation. There are numerous risk factors for suicide; singling out altitude, critics argue, is oversimplifying an extraordinarily knotty problem. Plus, brain biochemistry is itself highly complex and highly individualized. “There are some reasons to think altitude could have some impact,” says Dr. Richard McKeon, the chief of the U.S. Department of Health and Human Services’ suicide-­prevention branch. “But at this point, it’s not clear what the prevention implications would be.”

Still, interest in Renshaw’s re­search is growing. Two years ago, the Montana Department of Public Health and Human Services started recording the altitude of every suicide in the state. Karl Rosston, the agency’s suicide-prevention coordinator, says they’ve found that the average elevation at which Montana’s suicides occur is 3,508 feet and that about half of the people who took their own lives had moved from out of state.

Recently, Renshaw and his team started looking into why altitude might trigger depression. He thinks the explanation may lie with decreased oxygen, which starts to affect people right at that 2,000-foot Vegas threshold. At sea level, air consists of 21 percent oxygen. In Vegas, it drops to 19 percent, and at the top of Mount Everest, it’s around 7 percent. For some people, when their brains receive less oxygen, they start to produce less serotonin and more dopamine. Renshaw says that, in animals, serotonin levels can decline by as much as 30 percent in a day at altitude. A similar drop in a human brain could lead to devastating depression.

But this is where the science gets tricky. Everyone processes serotonin and dopamine in his own way. If someone is prone to low levels of serotonin, as is about a quarter of the U.S. population, elevation will likely make things harder, but if someone has normal serotonin levels and produces a lot of dopamine, he might actually feel better at elevation. “We call it the Utah paradox,” Renshaw says. “It’s the happiest and saddest place on earth.”