The Authors Reply

Gamboa et al. (2011) and others (Betz et al., 2011; DelMastro et al., 2011) have reported a higher incidence of depression with increasing altitude which supports other recent findings. Brenner et al. (2011) and Kim et al. (2011) have reported increased suicide rates (1979–1998 CDC Wonder) with increasing altitude on a county basis in the contiguous 48 United States (r=0.50) using two different county elevation modalities. These findings were confirmed in both firearm and non-firearm related suicides and began at 2000–2999 ft. Overall mortality, however, decreased with increasing altitude (r=−0.31). Similar positive correlation was found between altitude and suicide in Korea (Kim et al., 2011). These findings show that both depression and suicide increase with altitude, but overall mortality decreases with elevation.

Suicide is most often related to depression, and depression has been associated with hypoxia found at high elevations. There may be other differences to explain the findings of increased depression and suicide with increased altitude. There may be organismal differences in sleep apnea, periodic breathing, substance abuse, smoking, body mass index, or biochemical differences in serotonin metabolism, cellular respiration, or oxygen transport. The association with migraine would support more of a serotonin mechanism for the depression and may encourage increased pharmacologic serotonin modification as possible therapy. Other interventions for those amenable may involve supplemental oxygen, special monitoring, or moving to lower altitude.

Importantly, the observation by Brenner et al. (2011) that suicide rates begin to increase at altitudes as low as 2000 feet suggests that practitioners in mountainous regions need to be watchful for the emergence or worsening of depressive symptoms and migraine. This may also be true for other disorders that are linked to reduced serotonergic neurotransmission, especially anxiety disorders such as panic disorder and obsessive-compulsive disorder, and is likely to be more common in patients who have recently moved from lower altitudes.