Persons who committed suicide and lived at higher altitudes were significantly more likely to have bipolar disorder, compared with depression, schizophrenia, or anxiety disorders, researchers reported in the April issue of Medical Hypotheses.
Past research has found an association between altitude and suicide, even after controlling for gun ownership, rurality, age, and mental health access. The current study indicates that altitude preferentially affects suicide in bipolar disorder, said Rebekah S. Huber, a researcher at the University of Utah Brain Institute, Salt Lake City, and her associates.
Ms. Rebekah Huber
The researchers performed random coefficient logistic regression modeling and least squares means on data for 35,725 suicides in 16 states and 809 counties that occurred during 2005-2008 and were reported to the Centers for Disease Control and Prevention’s National Violent Death Reporting System. The investigators assigned every decedent a single major diagnosis of bipolar disorder, major depressive disorder, schizophrenia, or anxiety disorder, and excluded infrequent diagnoses such as posttraumatic stress disorder or eating disorder.
Living at higher altitude was significantly associated with having coefficient (P = .004) and logistic regression (P = .001) models. Persons with bipolar disorder committed suicide at a higher mean altitude (1,205 meters) than did decedents with anxiety disorders (1,181), major depressive disorder (1,116), or schizophrenia (1,057).
The reason for the effect merits further study but might be tied to underlying mitochondrial dysfunction in bipolar disorder, lower levels of environmental lithium at higher altitudes, or diminished efficacy of bipolar disorder treatments at higher elevations, the investigators said (Med. Hypotheses 2014;82:377-81).
"Metabolic stress due to hypoxia may have important considerations for individuals with [bipolar disorder]," they added. "Hypoxia due to reduced oxygen partial pressure at higher altitudes may further decrease mitochondrial function in individuals with BD. For these individuals, metabolic changes associated with hypoxia may lead to depression, instability of mood, and increased risk of suicide."
The researchers cited several limitations. For example, the findings are based on results from far less than half of the 50 states, but "many states in the intermountain West are included," they wrote.
The VISN 19 Mental Illness Research and Education Center, the Utah Science Technology and Research Initiative, and the National Institutes of Health funded the research. The authors reported no conflicts of interest.