Background: Cross-sectional studies have reported that certain long-term medical conditions are associated with major depression. Here, these associations are explored using a longitudinal analysis.
Methods: Data from the first (1994/95) and second (1996/97) waves of the Canadian National Population Health Survey (NPHS) were utilized. The first wave of the NPHS utilized a probability sample of 17626 members of the Canadian population. Members of this cohort were recontacted by Statistics Canada 2 years later. The Composite International Diagnostic Interview Short Form for Major Depression was used to identify episodes of major depression in both waves of the survey. Subjects free of major depression in the year preceding the 1994/95 survey were selected for inclusion in this analysis. The incidence of new-onset episodes in subjects with and without reported long-term medical conditions was compared.
Results: Individuals suffering from one or more long-term medical conditions were found to be at increased risk of major depression. Migraine headaches, sinusitis and back problems were the conditions most strongly associated with major depression. Having a long-term medical condition approximately doubled the risk of major depression in this analysis.
Limitations: The most important limitation of this study was its reliance on self report data about medical conditions.
Conclusions: A large proportion of the general population in Canada suffers from long-term medical conditions. These individuals are at increased risk of major depression. This study suggests an important role for long-term medical conditions in the etiology of major depression.