Why does the lifetime prevalence of major depressive disorder in the elderly appear to be lower than in younger adults? Results from a national representative sample.

Background: The explanation of the lower lifetime prevalence rate of major depressive disorder (MDD) in older adults compared to younger people in community surveys is debated. This study examines the hypothesis that the decrease of the lifetime prevalence of MDD in older adults may be due to an age-related difference in the lifetime prevalence of subthreshold hypomania and, to a lesser extent, to the increased rate of medical induced-depression.

Methods: Data were derived from the National Epidemiological Survey on Alcohol and Related Conditions (NESARC), a national representative sample of 43,093 adults of the United States population. We examined lifetime prevalence rates of pure MDD and MDD plus subthreshold hypomania (D(m)) by age, assuming that the lifetime prevalence of pure MDD in older adults would be similar to that in the youngest cohort, consequent to an inverse age-D(m) relationship. We further considered non-hierarchical MDD (i.e., general medical condition depressive disorders were not ruled out) with the same method.

Results: The lifetime prevalence of D(m) among depressed adults aged 65 years and over was substantially lower compared to the youngest group. When considering non-hierarchical MDD, the odds ratio of the lifetime prevalence estimates of non-hierarchical pure MDD in older adults compared to the youngest group appeared not significantly different from 1.

Conclusions: Findings indicate that the decrease of lifetime prevalence of MDD in older adults may be due to an age-related difference in the lifetime prevalence of subthreshold hypomania and, to a lesser extent, to the increased rate of medical induced-depression.