Research reportExcess mortality in depression: a meta-analysis of community studies
Introduction
The relationship between mortality and mental disorders has been examined systematically for more than 150 years (Brown, 1997, Pokorski, 1994). Most studies in this area have found mental disorders to be associated with an increased risk of death (Harris and Barraclough, 1998). The excess mortality in psychiatric disorders has been hypothesized to be caused by increased suicide rates (Pokorski, 1994), by hazardous health behaviors (smoking, less physical activity, unhealthy eating habits), and by higher incidence rates of accidental deaths because of hazardous activities.
In depressive disorders, it has been suggested that depression itself may cause physiological changes that enhance susceptibility to disease and, consequently lead to death (Penninx et al., 1999). Depressive disorders have been found to adversely affect endocrine, neurologic, and immune processes by increasing the sympathetic tone, decreasing vagal tone, and causing immunosuppression (Irwin et al., 1990, Lesserman et al., 1997). On the other hand, depressive disorders may be partly caused by physical disorders which are responsible for the increased mortality rates. In patients with established disorders, depression may also increase mortality rates by interfering with the patient’s motivation toward recovery, and by affecting compliance with treatment (Carney et al., 1995).
Most studies in this area have concentrated on patient samples (Harris and Barraclough, 1998). Because many mentally ill people do not seek help for their problems, and because it could be assumed that such patients are more ill than those not seeking help, these studies are biased, and may not be the best for examining the relationship between mortality and mental disorders.
In the last decades, several studies examining excess mortality in depression have been conducted in random samples of people living in the community. Most studies in this area indicate that there is excess mortality in depressed subjects, but this is not confirmed in all studies (Weissman et al., 1986, Bruce et al., 1994). One study even found a decreased mortality in subjects with major depression (Fredman et al., 1989). Because of the ambiguity of these results, we conducted a meta-analysis of these studies. In a meta-analyses the results of all studies in this field can be integrated statistically, and an overall mortality rate can be estimated.
Another issue that is examined in the current study concerns the differences in mortality rates between depressed men and women. In some studies in this field, higher mortality rates are reported for men than for women (Penninx et al., 1999, Murphy et al., 1987, Zheng et al., 1997), but in other studies no significant differences are found (Pulska et al., 1998, Roberts et al., 1990).
We also examine differences in excess mortality between subjects with major depression and subjects with subclinical forms of depression. Intuitively, it would make sense if major depression were associated with higher mortality rates than subclinical depression. But, some studies report equally increased mortality rates in subjects with major and in subjects with minor or subclinical forms of depression (Fredman et al., 1989, Sharma et al., 1998, Penninx et al., 1999).
Section snippets
Selection of studies
Studies were traced through several computerized literature databases (Medline, 1966–October 2000; Psychinfo, 1960–October 2000), using ‘depression’ and ‘mortality’ as key words. In the computerized databases abstracts were read and papers which possibly met inclusion criteria were collected. Reference lists of retrieved papers were screened, and papers that possibly met inclusion criteria were retrieved and studied.
In order to be included in the meta-analysis the study had to report on a
Overall RR of mortality in depressed versus not depressed subjects
A meta-analysis of all comparison groups resulted in a mean RR of 1.81 (95% CI: 1.58–2.07). The results of this meta-analysis are summarized in Fig. 1.
The chi-square test showed that there was considerable heterogeneity in the sample of comparisons. We examined which studies contributed most to the chi-square statistic, indicating a high contribution of the heterogeneity of the total sample. We removed the comparison that contributed most to the heterogeneity of the sample, and then removed the
Discussion
This study has several limitations. First, we only examined uncorrected RRs of mortality in depressed subjects. Corrections for chronic illnesses, life-style and other important variables could not be made. Second, in the selected studies important differences existed between study designs, definition of depression, follow-up periods, included age groups, and populations. Third, the number of comparisons that could be made was relatively small. Because of these limitations, the results of this
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