ArticlesDepression, chronic diseases, and decrements in health: results from the World Health Surveys
Introduction
Depression is an important global public-health issue, both because of the relatively high lifetime prevalence ranging from 2% to 15% and because it is associated with substantial disability.1, 2 Rated as the fourth leading cause of disease burden in 2000, depression accounted for 4·4% of total disability adjusted life years (DALYs).3 It is also responsible for the greatest proportion of disease burden attributable to non-fatal health outcomes, accounting for almost 12% of total years lived with disability worldwide.1 Without treatment, depression has the tendency to assume a chronic course, be recurrent, and over time to be associated with increasing disability.4, 5
The comorbidity of depression with chronic physical diseases such as arthritis and diabetes is well recognised in developed countries.6, 7, 8, 9 Several studies have shown that there is an increased risk of having major depression in people with one or more chronic diseases.7, 10, 11 The degree to which these comorbid states exist at the global level has not been shown. With a growing elderly population, and the associated increase in prevalence of chronic medical conditions, a concomitant rise in the prevalence of depression is to be expected. In fact, projections indicate that after heart disease, depression is expected to become the second leading cause of disease burden by the year 2020.12
The increasing prevalence of chronic physical diseases and depression leads to the question of how these disorders compare in terms of their effect on overall individual health. The presence of self-reported chronic physical diseases such as angina, arthritis, asthma, and diabetes has been associated with reduced health-related quality of life scores.13, 14, 15, 16, 17, 18, 19 Lower health status has been reported in depressed patients than in those without depression, and this state is unequally distributed across population groups.7, 13, 20, 21, 22 Effects of depressive episodes have also been studied with regard to loss in productivity and poor health-related quality of life.13, 21, 23, 24, 25, 26 Despite this evidence, depression, like other mental disorders, is often not deemed to be on a par with other chronic physical health conditions in terms of its effect on overall health.27, 28 This view is perhaps one of the underlying reasons behind the lack of parity between mental and physical disorders in terms of access to health care.6, 29, 30, 31, 32 To our knowledge, there has been no worldwide comparison of depression with other chronic diseases and their effect, either individually or comorbid, on health.
We analysed data from the WHO World Health Survey (WHS) to address the following questions: how does the decrement in health state associated with depression compare with the decrement associated with other common chronic physical conditions; and what is the added effect on decrements in health of suffering from depression, over and above a chronic physical condition?33
Section snippets
Sample
Countries from the WHS were selected to represent all regions of the world, with 26 countries from the European region, 15 from the African region, six from the Americas, four from the eastern Mediterranean region, five from the southeast Asia region, and four from the western Pacific region, giving a total of 60 countries. The countries included in the survey programme represent those countries that were willing and able to participate in the survey. Countries with samples that were nationally
Results
The prevalence for depression alone, each chronic disease alone, depression with each chronic physical disease, and having multiple chronic conditions with or without depression for 60 countries was estimated with CIs (results not shown, available on request). At the worldwide level, the prevalence for having any one condition alone did not exceed 5·0%. The prevalence of having diabetes alone had the lowest overall prevalence of 2·0% (1·8–2·2). However, since diabetes prevalence was based on
Discussion
The worldwide prevalence of depression, asthma, angina, arthritis, and diabetes based on data collected in the World Health Surveys, and used in the analysis presented here, are similar to the data reported by WHO's Global Burden of Disease study.44 The data show that comorbidity between chronic physical conditions and depression is common, and that people with chronic diseases are significantly more likely to suffer from depression than those without (p<0.0001). Our data indicate that
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