Original articleMedical disorders affect health outcome and general functioning depending on comorbid major depression in the general population
Introduction
Many previous studies have demonstrated that major depression significantly impairs health-related quality of life (HR-QoL), general functioning, and work productivity, and causes significant individual and economic burden with direct and indirect costs of illness [1], [2], [3], [4], [5]. Epidemiological studies show that depression is associated with substantial work impairment [5], [6], and experimental studies indicate that adequate depression treatment can substantially reduce work impairment [7]. Since major depression shows a consistent prevalence of about 15% in general hospital patients [8] and is associated with increased somatic symptoms, morbidity, mortality, health care utilization, and costs in individuals with comorbid medical disorders [9], [10], [11], [12], [13], it is recognized as an important and frequent comorbid condition in medically ill patients [9]. The effects of untreated major depression on general functioning are at least equal to those of many somatic conditions, including low-back pain, arthritis, diabetes, and cardiac disease [14].
Available knowledge on the association of depression, medical comorbidity, HR-QoL, health care utilization, and disability/work productivity largely relies on clinical studies with selection bias for certain medical conditions, medical disciplines, and age groups. Most of these studies investigated either patients of a certain age group exhibiting a higher prevalence of medical conditions (e.g., elderly patients) or patients with specific medical conditions (e.g., heart failure, renal diseases, and asthma) [10], [11], [13], [15], [16]. These clinical studies may lack representativeness and generalizability, as opposed to studies in the general population. Interestingly, studies estimating loss of work productivity due to depression have not yet been carried out in relation to comorbid medical disorders [6], [17]. However, the few general population studies on the outcome of comorbidity between medical conditions and depression are limited by the self-reported assessment of medical conditions without further medical verification and do not relate work productivity in depression to medical disorders at the general population level [18], [19], [20], [21].
The aim of this study is to compare HR-QoL, disability/work productivity, and health care utilization in a variety of medical disorders with and without comorbid major depressive disorder (MDD) in the general population. The paper addresses the following specific aims. First, we analyze the effects of various entities of medical disorders with and without MDD on HR-QoL expressed by the physical and the mental summary scores of the SF-36. Second, we examine the impact of the quantity of medical disorders on physical and mental HR-QoL among subjects with and without comorbid MDD. Third, we investigate the effect of MDD on the utilization of outpatient doctor visits, depending on specific entities of comorbid medical diseases. Fourth, we explore the effect of MDD on disability among subjects in the workforce compared to those currently not belonging to the workforce in relation to specific entities of comorbid medical disorders.
Section snippets
Sample
The German Health Interview and Examination Survey consisted of a core survey (GHS-CS) and several supplemental surveys, including the mental health supplement (GHS-MHS). The study was commissioned by the German Ministry of Research, Education, and Science, and was approved by relevant institutional review board and ethics committee. It used a stratified random sample from 113 communities throughout Germany with 130 sampling units [random sampling steps: (a) selection of communities; (b)
Comorbidity and HR-QoL
First, we looked at the effects of the entity of medical disorders on HR-QoL. MDD was significantly more frequent in allergic, neurological, and gastrointestinal diseases (Table 2). The physical summary score was significantly reduced in all medical disorders compared to that in subjects without medical disorders, regardless of MDD. The effects for allergic and neurological disorders disappeared after Bonferroni correction for multiple testing. In the presence of comorbid MDD, further
Discussion
In this population-based study, we investigated the effects of various medical disorders on HR-QoL, health care utilization, and disability/work productivity. As opposed to clinical studies with a possible help-seeking bias, the sample can be regarded as representative of the adult population aged 18–65 years.
Consistent with previous studies that employed a variety of instruments to measure HR-QoL [35], [36], [37], [38], [39], our study demonstrates substantial impairment in HR-QoL in the
Acknowledgments
This study was supported by grant 01EH970/8 (German Ministry of Research, Education, and Science). Mental disorders were assessed with the mental health supplement of the GHS-MHS (Max-Planck-Institute of Psychiatry, Munich; primary investigator: H.-U. Wittchen) and with physical conditions of the GHS-CS (Robert Koch-Institute, Berlin; primary investigators: B.-M. Kurth and W. Thefeld).
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