Incidence of major depressive episode correlates with elevation of substate region of residence

Background: Major depressive disorder (MDD) is a common disorder that is often associated with suicide. We have recently suggested that elevation may play a role in regional variations in rates of suicide. We hypothesize that there is also a significant correlation between incidence of MDD and elevation of residence. Methods: The substate estimates from the 2004 to 2006 National Surveys on Drug Use and Health (NSDUH) report from SAMHSA was used to extract substate level data related to percentages of people 18 years or older who experienced serious psychological distress or a major depressive episode in the past year. Mean elevation of each substate region was calculated by averaging the weighted elevations of its relevant counties. Average elevation for United States counties was calculated using the Shuttle Radar Topography Mission (SRTM) elevation dataset. Pearson correlation coefficients were computed to investigate the association between average substate elevation and rate of serious psychological distress or major depressive episode. Results: There was a significant correlation between percentage of people experiencing serious psychological distress in the past year in a substate region and that substate region's mean elevation (r = 0.18; p = 0.0005), as well as between the percentage of people having at least one major depressive episode in the past year in a substate region and that substate region's mean elevation (r = 0.27: p < 0.0001). Conclusions: Elevation appears to be a significant risk factor for MDD. Further studies are indicated to determine whether the increased incidence of depression with increased elevation may be due to the hypoxic effects on subjects with MDD. (C) 2010 Elsevier B.V. All rights reserved.