Objective: To determine whether diabetes mellitus (DM) with minor depression is associated with poorer levels of mental and physical functioning compared with DM without depression.
Study Design: Retrospective database study.
Methods: US adults participating in the 2001 Medical Expenditure Panel Survey were included in these analyses. Main outcome measures were differences in health status, physical and cognitive limitations, and the Short-Form 12 (SF-12) Mental Component Summary (MCS) and Physical Component Summary (PCS) for US adults with DM stratified by minor depression status and evaluated using univariate and multivariate analyses to control for demographic, behavioral, and clinical covariates.
Results: A total of 1572 respondents with DM were included (1443 without depression, 129 with depression). Compared with people with DM and without depression, those with DM and minor depression were younger (P = .04); were more likely to be female, white, and smokers; and to have physical and cognitive limitations and lower SF-12 MCS and PCS scores (all P < .01). In multivariate analyses, minor depression was independently associated with lower self-reported health status, MCS scores, and more cognitive limitations.
Conclusion: People with DM and minor depression have lower mental functional scores, more cognitive limitations, and lower self-reported health status scores compared with people with DM and without depression, differences that may adversely affect self-care activities. Primary and DM care providers should screen for and be aware of depression in their patients with DM.
(Am J Manag Care. 2007;13:65-72)
Almost 21 million Americans have diabetes mellitus (DM),1 and approximately 19 million Americans suffer from depression.2 Significant morbidity, mortality, and resource use are associated with each disease. The American Diabetes Association reports that the risk for heart disease and stroke among people with DM is twice that of people without DM.1 Direct and indirect medical costs associated with DM in 2002 were an estimated $132 billion, and there were more than 12 million office visits during 2004 for depression.3,4 Beyond the clinical and economic impact of each disease on healthcare systems in the United States, DM and comorbid depression present additional healthcare challenges for 2 reasons. First, the estimated prevalence of depression among people with DM is more than twice that among the general population, and second, comorbid DM and depression are associated with poor glycemic control.5,6
Both DM and depression are associated with increased disability. Among people with DM, those with depression have higher levels of work disability or overall functional disability (ie, non-work-related) compared with those without depression.7,8 By 2020, major depression is projected to be second only to ischemic heart disease as a cause of disability.9 Compared with DM without depression, DM with both major and minor depression is associated with increased work disability/unemployment, inability to go to work 5 or more days in the previous month, or inability to perform tasks while at work.10 Comorbid major depression and DM are associated with more disability days and increased odds of lost work days compared with DM without depression.11
A synergistic effect between DM and depression in which the presence of both diseases is associated with more functional disability than the presence of either disease alone also has been described.12-14 Among people with DM, the presence of depressive symptoms is associated with impairment in activities of daily living (ADLs) and instrumental activities of daily living (IADLs), and an increased risk of dying compared with those without depressive symptoms.12,13 The presence of both DM and major depression is associated with more functional disability.14 Adults with DM and comorbid major depression have more difficulties maintaining health, diet, and exercise recommendations and are less likely to be adherent with prescribed medications compared with people with DM and without major depression.15 These studies involved either specific subpopulations (ie, Mexican-Americans)12,13 or major depression and DM in the general population.14,15
Diabetes self-management is an essential component necessary for achieving glycemic control and avoidance of DM-related complications. Treatment of DM is multidimensional, involving complex diet, exercise, self-monitoring, and medication regimens. Although associations between major depression and difficulties managing diet, exercise, and medication have been reported,14,15 studies investigating similar challenges presented by DM and comorbid minor depression are lacking. The need exists for investigations of the association between minor depression and functional disability in patients with DM in large, nationally representative populations. The current study addresses that need by evaluating associations between comorbid DM and minor depression and functional status. Data for these analyses were obtained from the Medical Expenditure Panel Survey (MEPS), a nationally representative survey of the US civilian noninstitutionalized population.16 We hypothesized that minor depression among US adults with DM is associated with poorer levels of mental and physical functioning compared with the levels observed in people with DM and without depression.
The 2001 MEPS Household Component (MEPS HC) database was used for all analyses. MEPS is cosponsored by the Agency for Healthcare Research and Quality and the National Center for Health Statistics. The sampling frame for the MEPS HC is drawn from respondents to the National Health Interview Survey. The MEPS HC collects data from a subsample of respondents to the previous year's National Health Interview Survey, generating a nationally representative database. For each survey year, MEPS data are collected in 3 rounds that cover the entire year. Therefore, data for diagnoses of medical conditions and prescription use are recorded in the same survey year.
The sample design of the MEPS HC survey includes stratification, clustering, multiple stages of selection, and disproportionate sampling, with sampling weights that reflect adjustments for survey nonresponse and population totals from the Current Population Survey.17 All analyses were conducted using STATA 8.1 (StataCorp, College Station, Tex) to account for the complex sampling structure of MEPS, ensuring nationally representative estimates.
Subjects were identified through use of the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM).18 All MEPS participants with ICD-9-CM code 250 (diabetes mellitus) for 2001 who were between the ages of 18 and 89, inclusive years were included in this study. MEPS limits ICD-9-CM codes to 3 digits to ensure privacy for respondents. No differentiation is made in the database with regard to diagnosis of type 1 or type 2 DM for MEPS respondents. For the purpose of these analyses, minor depression was defined as depression not meeting the Diagnostic and Statistical Manual of Mental Disorders criteria for major depression (ICD-9-CM code 296).19 Respondents with ICD-9-CM code 311 (depression not otherwise specified), along with at least 1 prescription for an antidepressant drug (eg, monoamine oxidase inhibitors, tricyclic antidepressants, selective serotonin reuptake inhibitors, serotonin 2 receptor antagonists, a2 receptor antagonists, and other miscellaneous antidepressants) were defined as having DM and minor depression. To avoid misclassification bias, respondents with a diagnosis code consistent with major depression (ICD-9-CM code 296) and those with a diagnosis code for minor depression (ICD-9-CM code 311) but without an antidepressant medication were excluded from the analyses. The resulting 2 cohorts included people with diabetes: 1 cohort with minor depression and 1 cohort with no depression.
Approval for this study was obtained from the Colorado Multiple Institutional Review Board.
Seven outcomes measures related to functioning were available for study in the MEPS database, 3 related to health and functional status and 4 related to limitations in physical or cognitive functioning, ADLs, or IADLs. The health status measures included the Short-Form 12 (SF-12), which was administered to participants of the MEPS survey as part of the Self-Administered Questionnaire (SAQ).20 Components of the SAQ included the 12 questions of the SF-12, compiled into Mental Component Summary (MCS) scores and Physical Component Summary (PCS) scores, and a question asking respondents to estimate their perceived general health status using a visual analog scale (VAS) ranging from 0 ("worst possible health") to 100 ("best possible health"). As a result, VAS scores represent the respondents' perception of their overall health, or their self-rated health status.21 The SF-12 is a validated, generic health status measure that provides scores for physical and mental condition (SF-12 PCS and SF-12 MCS scores) that are based on each respondent's answers to 12 questions regarding physical and mental health.20
Cognitive limitations were assessed for individual respondents by surveying family members. The variable was coded as yes if an adult in the family was reported to (1) have experienced confusion or memory loss, (2) have problems making decisions, or (3) required supervision for his or her own safety. Physical limitations were assessed using a composite variable that included limitations in walking, activities, seeing, hearing, ADLs, and IADLs. A limitation in any of the categories was coded as a yes to physical limitations, whereas a no in all categories indicated the absence of any physical limitations. Variables for cognitive and physical limitations reflect patient (or family) responses to MEPS questionnaire items.
The variables corresponding to ADLs and IADLs also were examined separately. Difficulties with ADLs indicated problems with the ability to perform daily tasks such as bathing, dressing, eating, walking across a room, getting in/out of bed, and using a toilet independently.22 Difficulties with IADLs indicated problems with the ability to perform instrumental tasks such as preparing meals, shopping, managing money, using the telephone, and taking medications independently.23 Responses for ADL and IADL questions were compiled into a dichotomous variable where yes indicated the presence of at least 1 limitation and no indicated the absence of all limitations.