Over a six-year period, Aartjan T. F. Beekman, M.D., Ph.D., and his Dutch colleagues studied the natural history of depression among men and women aged 55 to 85 years.
Their 277 participants were subjects in the Longitudinal Aging Study Amsterdam, a 10-year study of the elderly, and all participants had previously been diagnosed with depression. The average age was 71.8 years, and about 65 percent were women.

Interviews were conducted at the beginning of the study, at three years, and at six years. Between interviews, participants completed questionnaires sent through the mail every five months for the first three years and every six months for the last three years. At each interview, an individual's form of depression was identified using the Diagnostic Interview Schedule, a common test in epidemiological research of the elderly. Four types emerged: subthreshold depression (207 participants), dysthymia (a mild, chronic form of depression) (25 participants), major depressive disorder (23 participants), and a combination of dysthymia and major depressive disorder (22 participants).

An analysis of remission in the four diagnostic subgroups revealed that persons with subthreshold depression were most likely to have recovered by the end of the study. Those with a combination of dysthymia and major depressive disorder faced the most serious prognosis---Few participants diagnosed with this disorder recovered within the six-year follow-up period. In addition, persons who were 75 to 85 years old at the beginning of the study had more severe and persistent symptoms than younger participants.

After analysis of the severity and duration of symptoms over the six-year period, the researchers found that 23 percent of participants had true remissions, 12 percent had remission with a few recurrences, 32 percent had more than one remission followed by a persistent recurrence of symptoms, and 32 percent had chronic depression. The authors stated in the article that figures totaled 99 percent due to rounding of numbers.

The authors conclude "The implications of the study are that the burden of depression for elderly persons in the community is even more severe than previously thought. The data clearly demonstrate the need for interventions that are helpful, acceptable, and economically feasible to be performed on a larger scale."