Objective: Most research on the association between sleep disturbances and depression has looked at cross-sectional data. The authors used two waves of data from a panel study of community residents aged 50 years or more to investigate this issue prospectively.
Method: Data on symptoms of major depressive episodes and sleep problems were examined for a subgroup of the 1994 and 1995 surveys of the Alameda County (California) Study (N=2,370). The authors examined the effects of age, gender, education, marital status, social isolation, functional impairment, financial strain, and alcohol use. Depression was measured with 12 items that covered the DSM-IV diagnostic criteria for major depressive episodes, including insomnia and hypersomnia.
Results: The prevalences were 23. 1% for insomnia and 6.7% for hypersomnia in 1994. Sleep was a significant correlate of depression, as were being female, older age, social isolation, low education, financial strain, and functional impairment. When sleep problems and depression were examined prospectively, with controls for the effects of the other variables, sleep problems in 1994 predicted depression in 1995. However, other symptoms of major depressive episodes-anhedonia, feelings of worthlessness, psychomotor agitation/retardation, mood disturbance, thoughts of death-were much stronger predictors of future major depression.
Conclusions: Sleep disturbance and other symptoms that are diagnostic for major depression are strongly associated with the risk of future depression. Sleep disturbance appears to be a less important predictor of depression. More epidemiologic research is needed on the relative contributions of the range of depressive symptoms to the risk of clinical depression.