a1 Department of Health Care Policy, Harvard Medical School, Boston, MA, USA
a2 The Analysis Group, Boston, MA, USA
a3 Department of Psychiatry and Behavioral Sciences, State University of New York at Stony Brook, Stony Brook, NY, USA
a4 Boston Psychoanalytic Society and Institute, Boston, MA, USA
Background Although depression appears to decrease in late life, this could be due to misattribution of depressive symptom to physical disorders that increase in late life.
Method We studied age differences in major depressive episodes (MDE) in the National Comorbidity Survey Replication, a national survey of the US household population. DSM-IV MDE was defined without organic exclusions or diagnostic hierarchy rules to facilitate analysis of co-morbidity. Physical disorders were assessed with a standard chronic conditions checklist and mental disorders with the WHO Composite International Diagnostic Interview (CIDI) version 3.0.
Results Lifetime and recent DSM-IV/CIDI MDE were significantly less prevalent among respondents aged 65 years than among younger adults. Recent episode severity, but not duration, was also lower among the elderly. Despite prevalence of mental disorders decreasing with age, co-morbidity of hierarchy-free MDE with these disorders was either highest among the elderly or unrelated to age. Co-morbidity of MDE with physical disorders, in comparison, generally decreased with age despite prevalence of co-morbid physical disorders usually increasing. Somewhat more than half of respondents with 12-month MDE received past-year treatment, but the percentage in treatment was lowest and most concentrated in the general medical sector among the elderly.
Conclusions Given that physical disorders increase with age independent of depression, their lower associations with MDE in old age argue that causal effects of physical disorders on MDE weaken in old age. This result argues against the suggestion that the low estimated prevalence of MDE among the elderly is due to increased confounding with physical disorders.
(Received February 20 2009)
(Revised April 27 2009)
(Accepted May 03 2009)
(Online publication June 17 2009)