Several depressive disorders are described in the Diagnostic and Statistical Manual for Mental Disorders (4th
Edition; DSM-IV; American Psychiatric Association, 1994
), including major depressive disorder, dysthymic disorder, bipolar disorder and mood disorder due to a general medical condition. Adjustment disorder with depressed mood may also be considered a form of depression.
Much attention has recently been given to the experience of depressive symptoms that do not fulfill the criteria for a diagnosis of major depressive disorder. Some research has investigated this phenomenon using more or less well-defined categories, e.g., minor depression, subsyndromal depression, etc., whereas other investigators have defined clinically significant depressive symptoms as a score above a threshold on a depressive symptom checklist. Some (Judd, Schettler, & Akiskal, 2002
) but not all (Ruscio, Zimmerman, McGlinchey, Chelminski, & Young, 2007
) evidence suggests that depression may occur on a spectrum, with symptoms that do not meet syndromal criteria for major depressive disorder representing a less severe manifestation of the same disorder. In older adulthood, the prevalence of major depressive disorder differs from that of clinically significant depressive symptoms, as we discuss below. Nonetheless, in most cases the same risk and protective factors are associated with both. Where differences have been documented, we so indicate. In the present review, we focus primarily on major depressive disorder.
The prevalence of major depressive disorder at any given time in community samples of adults aged 65 and older ranges from 1-5% in most large-scale epidemiological investigations in the United States and internationally, with the majority of studies reporting prevalence in the lower end of the range (e.g., Hasin et al., 2005
). Clinically significant depressive symptoms are present in approximately 15% of community-dwelling older adults (Blazer, 2003
). Rates of depression appear to be higher in older women than in older men, but with the gender gap somewhat narrower in this age group, particularly among the oldest old, than the two-fold difference seen across the rest of the adult lifespan (Djernes, 2006
). There are few differences in depression prevalence by race or ethnicity, although depressive symptoms may be more common among Hispanic older women than non-Hispanic whites (Swenson, Baxter, Shetterly, Scarbro, & Hamman, 2000
Rates of major depression among older adults are substantially higher in particular subsets of the older adult population, including medical outpatients (5-10%, though estimates vary widely), medical inpatients (10-12%), and residents of long term care facilities (14 to 42%; Blazer, 2003
; Djernes, 2006
). Congregate living arrangements are not depressogenic per se, as shown by the lower rate of depression found among older kibbutz residents compared to community samples (Blumenstein et al., 2004); rather, relocation to congregate living is typically occasioned by health issues and/or loss of a caregiving spouse.
Prevalence of major depression in community samples of older adults reflects a significant decline from midlife prevalence rates for both men and women. In contrast, most studies that measure elevated scores on a depressive symptom checklist (rather than diagnosis of a depressive disorder) report higher rates of clinically significant depressive symptoms among older adults than in midlife (Newmann, 1989
). How should these differences in prevalence be interpreted? The diagnostic rubric for major depressive disorder may underestimate disorder among older adults. Current diagnostic criteria privilege dysphoria, a symptom less frequently endorsed by older adults compared to younger adults (Gallo, Anthony, & Muthén, 1994
), and require a judgment that symptoms are not attributable to the direct physiological effects of a medication or general medical condition, or to a recent bereavement. Conversely, depressive symptom checklists are inflated, as they do not exclude symptoms that are directly linked to a physical illness or bereavement, both of which increase in frequency with age. As Blazer (2003)
and others have demonstrated, depressive symptoms actually decrease in frequency with age after accounting for the effects of gender, education, physical illness and bereavement, though it should be noted that physical illness and bereavement can be causes of depression rather than simply confounds. Thus, the preponderance of evidence indicates that depression becomes less common and less severe with age, but that lower-severity depressive symptoms, which can also be consequential and treatable (Judd et al., 2002
), should not be overlooked. We elaborate reasons for age differences in depressive symptom prevalence below; first we turn to age differences in presentation of depression.