The eight intermountain states of the American West,
sometimes called the Suicide Belt, have high elevations and the associated thin
air. Now, researchers say the low oxygen in these areas is linked with signs of
depression, and could potentially even contribute to suicides in some regions.
In 2012, Colorado, Wyoming, Utah, Montana, Idaho, Nevada,
Arizona and New Mexico all had suicide rates exceeding 18 per 100,000 people,
while the national rate was 12.5 per 100,000 people, according to the American
Foundation for Suicide Prevention.
These states tend toward higher elevations, and several
studies have identified living at higher elevations as risk factor for suicide.
In one of previous studies, researchers noted a correlation between state
altitude and suicide in the United States, which could be explained by higher
rates of gun ownership and lower population density in the intermountain West.
The team's latest study suggests that high-altitude living is an independent
risk factor for suicide. Other studies have also found that rates of depression
increase with elevation and may contribute to increased suicide risk.
In a novel study, University of Utah (U of U) researchers
have shown that hypobaric hypoxia (the reduced oxygen experienced at high
altitude) can lead to depression.
In the March 2015 edition of High Altitude Medicine and
Biology online, the U of U researchers and a colleague from Tufts University show
that female rats exposed to high-altitude conditions, both simulated and real,
exhibit increased depression-like behavior. Male rats, interestingly, showed no
signs of depression in the same conditions.
“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,” says Shami
Kanekar, Ph.D., research assistant professor of psychiatry and lead author on
the study.
The researchers housed rats for a week at simulated
altitudes of sea level, 10,000 feet and 20,000 feet using altitude chambers,
and at local conditions of 4,500 feet, the elevation of Salt Lake City where
the research took place. They then used a widely accepted behavioral test in
which depression is gauged by how much persistence rodents demonstrate in a
swim test. “In female rats, increasing altitude of housing from sea level to
20,000 feet caused a parallel increase in depression-like behavior,” Kanekar
says.
Several studies, including work by Perry F. Renshaw, M.D.,
Ph.D., M.B.A., USTAR professor of psychiatry at the U of U and senior author on
this latest study, suggest altitude is an independent risk factor for suicide,
and further that depression rates also increase with altitude and may
contribute to the increased suicide risk.
Because rats are not subject to the same psychological
and societal pressures as people, the current study bolsters the argument that
physiological changes triggered by hypobaric hypoxia (the low oxygen at high
altitude) can contribute to depression. What these changes are, and whether
they also occur in people, will be the subject of future studies.
“There are many potential risk factors that contribute to
depression and suicide at altitude, and we are not discounting any of these
other factors at all,” says Renshaw. Several such factors that are prevalent in
the Intermountain West include poverty, rural residence, low population
density, gun ownership and psychiatric disorders such as bipolar disease. “But
this new study shows that one factor inherent to living at altitude–hypobaric
hypoxia–can cause depression. Hypobaric hypoxia thus clearly is linked to the
high depression rates in regions of altitude, and this factor may need to be
addressed.”
According to Renshaw, a potential cause for depression at
altitude might be found in low levels of serotonin, a neurotransmitter that is
thought to contribute to feelings of well-being and happiness. Hypoxia impairs
an enzyme involved in synthesis of serotonin, likely resulting in lower levels
of serotonin that could lead to depression. In addition, Renshaw’s group has
shown that brain cellular metabolism can be damaged by hypoxia in rats as well
as in humans.
This deficit in brain function may contribute to what
Renshaw calls “The Utah Paradox”. Despite having the highest use of
antidepressants in the country, Utah also has the highest Depression Index, as
defined by a National Mental Health Survey in 2007. Animal studies imply that
SSRIs such as Prozac® may not work when brain serotonin levels are low. In
current studies, Kanekar and Renshaw are therefore evaluating the effectiveness
of currently available antidepressants in hypobaric hypoxia, with a major focus
on SSRIs, the most commonly prescribed antidepressants in the United States.
Future studies involve exploring novel therapeutic options for hypoxia-related
depression.
“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.
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