Depression may be understood as a spectrum of more or less symptomatic states. Little is known about the long-term course of these states in older populations. We examined the prevalence and course of depressive states of different severity in a Swedish population sample of older people followed over 9 years.
A population-based sample of 70-year olds without dementia (N = 563, response rate 71.1%) underwent a psychiatric examination; 450 survivors without dementia were reexamined at ages 75 and/or 79 years. Three depressive spectrum states were defined: major depression (MD), minor depression (MIND), and subsyndromal depression (SSD).
The cumulative 9-year prevalence of any depressive spectrum state was 55.3% (MD 9.3%, MIND 27.6%, SSD 30.9%). The cross-sectional prevalence increased with age, especially for MIND and SSD. Among those with baseline MD and MIND, 75.0% and 66.7%, respectively, had MD or MIND during follow-up. Among those with SSD, 47.2% had SSD also during follow-up and 36.1% had MD or MIND. Among those with MD during follow-up, 63.1% were in a depressive spectrum state at baseline. The corresponding proportion was 30% for those with MIND (but no MD) during follow-up.
In this population-based sample, over half experienced some degree of depression during their eighth decade of life. The findings give some support for the validity of a depressive spectrum in older adults. Most new episodes of major depression occurred in people who were in a depressive spectrum state already at baseline, which may have implications for late-life depression prevention strategies.