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Question Is depression associated with increased mortality and suicide?
English language studies were identified by searching Medline, PsycINFO, and Health databases (from their inception to 1996) using the terms depression and affective disorders combined with mortality and death. Informal searches were also done.
Inclusion criteria were assessment of the contribution of depression to the risk of death; depressive symptoms or depressive disorders assessed using clinical diagnosis, structured interview, or a standard symptom inventory; and mortality rates compared for the depressed sample and a comparison group. Studies of bereavement or single symptoms of depression were excluded.
Data were extracted on study quality and characteristics including sample size, measure of depression, choice of comparison group, factors controlled for in the analyses, mortality and suicide rates, and strength of evidence.
57 studies met the inclusion criteria. 29 studies (51%) reported that depression was associated with increased mortality, 13 (23%) did not find an association, and 15 (26%) had mixed results (eg, increased mortality for only some subgroups). 21 studies were considered to have high quality methods. Relative mortality was measured by mortality ratios in 31 studies (range 0.6 to 7.3), relative risks in 15 studies (range 0.82 to 2.1), and odds ratios in 8 studies (range 1.1 to 7.8). 18 studies of psychiatric patients assessed by psychiatric examination had a weighted mean mortality ratio of 2.7 (range 0.6 to 7.3). 5 studies of people in the community assessed by self report had a weighted mean relative risk of 1.2 (range 0.82 to 1.6). The 4 high quality studies in community or medical settings with patients assessed by structured interview, and which adjusted for physical illness, had a weighted mean relative risk of 1.7 (range 1.6 to 1.8).
35 studies reported rates of suicide as a per cent of deaths in people who were depressed (range 0% to 64%, mean 10.8%). For the 23 studies of psychiatric patients, suicide range was similar with a mean of 16%. 9 high quality studies reported suicide rates (range 0% to 31%, mean 7.3%) and 3 high quality studies reported rates for psychiatric patients (range 2.4% to 31%, mean 19.1%).
25 studies reported data on cardiovascular mortality and depression: 15 reported an increased risk, 5 reported no increased risk, and 5 reported mixed results (increased risk for men but not women in 4 studies and increased risk for women and not men in 1 study). 18 studies provided data on deaths from cancer: 4 showed an increased risk for mortality, 11 showed no increase, and 3 had mixed results.
Depression is associated with an increased risk of mortality, although the studies had variable quality and methods. Cardiovascular mortality and suicide are also related to depression.
The World Health Organisation predicts that mood disorders will be the most prevalent public health problem in the 21st century.1 The current pervasiveness of depression and its personal and societal effects have prompted many investigations; however, few systematic reviews have been done. This review is important because it examines and synthesises previous publications about depression as it relates to mortality.
The review by Wulson et al is strong because it used a systematic method for data collection, analysis, and reporting. This allows the reader to draw conclusions based on a complete set of studies published in English and provides specific criteria for replication. A second strength is its breadth. Over 50 studies representing a wide variety of contexts and samples were included. This broad range revealed the relative chaos of designs and methodologies, leading the authors to their most important conclusion—most of these studies are substantially flawed. As a result, although most of the studies revealed a positive association between depression and mortality, the reader cannot assume the degree or source of the effect of depression on mortality.
The authors limited the inclusion of studies to those that were published and those that were written in English. They acknowledge that by including only published studies, there is the possibility of publication bias (ie, because fewer studies with findings of no difference are submitted and published, reliance on published studies may result in an over representation of positive findings in a review). Another strength of this review is the quality rating of the studies and the separate presentation of findings from the high quality studies. The authors caution that even among the “better studies,” most failed to control for >1 of the major mediating factors that the authors suggest also affect mortality: smoking, alcohol abuse, chronic physical illness, and suicide.
This is an important study for nurses because although it suggests a positive association between depression and mortality, it also exposes the limitations of published studies on the topic.
Source of funding: no external funding.
For correspondence: Dr L R Wulsin, Department of Psychiatry, 231 Bethesda Avenue, ML 559, Cincinnati, OH 45267, USA. Fax +1 513 558 4805.