Objective: The purpose of this study was to examine the comorbidity of and communality of risk factors associated with major depressive disorder and anxiety disorders in later life.
Method: A random age- and sex-stratified community-based sample (N=3,056) of the elderly (age 55-85 years) in the Netherlands was studied. A two-stage screening design was used, with the Center for Epidemiologic Studies Depression Scale as a screening instrument and the National Institute of Mental Health Diagnostic Interview Schedule as a criterion instrument. Risk factors were measured with well-validated instruments and represented a broad range of vulnerability and stress-related factors associated with anxiety and depression. Multivariate analyses examined risk factors associated with pure major depressive disorder, pure anxiety disorders, and comorbid conditions.
Results: Comorbidity was highly prevalent: 47.5% of those with major depressive disorder also met criteria for anxiety disorders, whereas 26.1% of those with anxiety disorders also met criteria for major depressive disorder. While the only variables associated with pure major depressive disorder were younger age and external locus of control, risk factors representing a wide range of both vulnerability and stress were associated with pure anxiety disorders. External locus of control was the only common factor. The group with anxiety disorders plus major depressive disorder had a distinct risk factor profile and may represent those with a more severe disorder.
Conclusions: Although high levels of comorbidity between major depressive disorder and anxiety disorders were found, comparing risk factors associated with pure major depressive disorder and pure anxiety disorders revealed more differences than similarities. Anxiety disorders in later life merit separate study.