Major Depression Prevalence Increases with Latitude in Canada

Area of Science:

• Epidemiology
• Mental Health Research
• Geographical Health Studies

Background:

• Major depressive episode (MDE) is a significant public health concern.
• Geographical variations in MDE prevalence are not well understood.
• Previous studies have not reported a latitude gradient for MDE.

Purpose of the Study:

• To investigate the association between latitude and the prevalence of annual MDE in Canada.
• To determine if higher latitudes correlate with increased MDE rates.

Main Methods:

• Utilized data from two large Canadian national surveys (1996-2013) with over 922,000 respondents.
• Assessed MDE using the Composite International Diagnostic Interview.
• Determined approximate latitude by linking respondent postal codes and employed meta-analytic methods.

Main Results:

• A statistically significant association was found between increasing latitude and higher MDE prevalence.
• The prevalence odds of MDE increased by 1% to 2% per degree of latitude.
• This latitude gradient was observed even after adjusting for known risk factors.

Conclusions:

• A novel latitude gradient in MDE prevalence was identified in Canada.
• This finding may inform public health service planning and etiological research.
• The cross-sectional nature of the study limits causal inference and evaluation of factors like light exposure.