Psychosomatics 49:109-114, March-April
doi: 10.1176/appi.psy.49.2.109
© 2008 Academy of Psychosomatic Medicine
Quality of Life in Individuals With Serious Mental Illness and Type 2 Diabetes
Faith Dickerson, Ph.D., M.P.H.,
Clayton H. Brown, Ph.D.,
LiJuan Fang, M.S.,
Richard W. Goldberg, Ph.D.,
Julie Kreyenbuhl, Pharm.D., Ph.D.,
Karen Wohlheiter, M.S., and
Lisa Dixon, M.D., M.P.H.
Received May 4, 2006; revised August 17, 2006; accepted August 30, 2006. From Sheppard Pratt–Stanley Research Center, 6501 N. Charles St., Baltimore, MD 21204. Send correspondence and reprint requests to Dr. Dickerson. e-mail: fdickerson{at}sheppardpratt.org
© 2008 The Academy of Psychosomatic Medicine
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ABSTRACT
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Diabetes is a pervasive metabolic disease that disproportionately affects persons with serious mental illness. The authors studied the effect of diabetes on quality of life in a sample of 369 adult outpatients with schizophrenia or major mood disorder, 201 of whom had type 2 diabetes. Patients with diabetes reported greater impairment in both physical and mental-health quality of life than those without diabetes. The diabetes patients also reported less satisfaction with health but not with other life domains. Medical providers need to be attentive to the burden of disease experienced by patients with both serious mental illness and diabetes.
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INTRODUCTION
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Diabetes is a persistent and complex metabolic disorder that affects 4% of the general population in the United States.1 Quality of life refers to well-being and functional status from the patient’s perspective, and it can be viewed as the single most important outcome domain for persons with persistent medical conditions such as diabetes.2 Numerous studies have now established that diabetes is associated with health-related decrement in quality of life. Compared with non-diabetic persons, those with diabetes are noted to have lower physical functioning, role functioning, energy level, and perception of their general health.2–5
Diabetes is even more prevalent among individuals with serious mental illness than it is in the general population, with estimated rates of 16% to 25% in schizophrenia.6 Rates of diabetes are also elevated in bipolar disorder7 and depression.8 For this reason, diabetes in serious mental illness has been the focus of heightened research attention. However, most studies to-date have been concerned with the incidence and prevalence of co-occurring diabetes in this population and the contributing role of antipsychotic medications. Few studies have examined the clinical correlates of diabetes in persons with serious mental illness.
As a group, persons with serious mental illness have reduced quality of life secondary to the effects of their often pervasive psychiatric disorders and co-occurring somatic health problems, which are also prevalent in this population.9,10 It is uncertain to what extent diabetes contributes to additional decrements in quality of life in persons with serious mental illness.
The purpose of the current study was to compare the quality of life of individuals with and without diabetes, all adults with serious mental illness.
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METHOD
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Sample
The sample of 369 adults was drawn from two cohorts of individuals with serious mental illness being evaluated about their health status; one cohort consisted of patients with type 2 diabetes.
Patients in the diabetes cohort included outpatients, age 18–65, with a chart diagnosis of type 2 diabetes, who were receiving psychiatric care at six mental health centers, including a local Veterans Administration Center, in the Baltimore area. Participants were enrolled to obtain a total of 100 individuals with schizophrenia or schizoaffective disorder and 101 with a major mood disorder, either bipolar disorder or recurrent major depression.11
The second cohort included randomly selected outpatients, age 18–65, who were receiving psychiatric care at two centers in the Baltimore area, both of which were also sites where the persons in the diabetes cohort were receiving mental health care. Participants were enrolled to obtain a total of 100 individuals with schizophrenia, half with schizophrenia excluding schizoaffective disorder, and half with schizoaffective disorder, and 100 individuals with a major mood disorder, half with major depression and half with bipolar disorder. Within each diagnostic group, patients were selected in random order until we obtained the predetermined number of consenting patients.12 Patients in this cohort who reported being diagnosed with "sugar" diabetes (N=27), gestational diabetes (N=4), or both (N=1) were deleted from the sample for purposes of this investigation, yielding a sample of 168 out of the original 200 patients.
Patients provided written informed consent after the study procedures were explained. The Institutional Review Board of the University of Maryland School of Medicine and each participating facility approved each study. Assessments of both cohorts were conducted between September 1, 1999, and September 30, 2002.
Characteristics of the individuals with and without diabetes who comprised the study sample used for this investigation are presented in Table 1.
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TABLE 1. Characteristics of the Study Sample (N=369), Individuals With Serious Mental Illness, With and Without Type 2 Diabetes
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Measures
All patients were interviewed with questions about smoking status and lifetime medical conditions as part of a larger assessment for each study. Specifically, patients were asked about the occurrence of cancer, high blood pressure, heart problems (congestive heart failure, stroke, coronary heart disease, angina, heart attack, or other heart conditions or disease), and respiratory problems (asthma, chronic bronchitis, emphysema, or other respiratory problem) with items from the National Health and Nutrition Examination Survey III13 or the National Health Interview Survey.14
Two quality-of-life instruments were utilized in order to tap the range of items and domains that are important in the measurement of overall quality of life and health-related quality of life of persons with serious mental illness: 1) the brief Quality of Life Interview (QOLI)15 was used to measure patients’ satisfaction with their life overall and with their life in seven specific domains (daily activity, family, social relations, financial, work, safety, health). The brief QOLI also includes self-report on objective functioning in three domains (family contact, social relations, and victimization); and 2) The Medical Outcomes Survey, Short Form–12 (MOS SF–12)16 was used to assess patients’ perspective of their health-related functional status. Domains evaluated were health-related physical functioning (PF) and social functioning (SF), role limitations due to physical health (RP) and emotional problems (RE), perceptions of mental health (MH) and general health (GH), bodily pain (BP), and vitality (V). Items are combined with predefined weights to generate a Physical composite score (PCS) and a Mental composite score (MCS).17
Data Analyses
We compared the diabetes and the non-diabetes groups on each outcome from the QOLI and the MOS SF–12. We first performed bivariate comparisons using the z statistic. Because of the large sample size, the z statistic and p value will be approximately equal to the comparable t statistic and p value. We then performed a regression analysis on each quality-of-life variable, adjusting for smoking status and the demographic variables of age, gender, race (Caucasian versus non-Caucasian), education (high school graduate versus non-high school graduate, diagnosis (schizophrenia-spectrum versus mood disorder), and veteran status. These covariates were selected because they are potential confounders in the association between diabetes status and quality-of-life outcomes in this population; we were not able to adjust for other potential confounders such as obesity, comorbid substance use, cognitive impairment, or the severity of psychiatric symptoms. We performed additional regression analyses on each quality-of-life variable in which we also adjusted simultaneously for each category of non-diabetes co-occurring medical condition that had been assessed.
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RESULTS
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Overall Quality of Life
In bivariate comparisons, as shown in Table 2, patients with diabetes reported less subjective satisfaction with their health than those without diabetes. There were no significant differences between the two groups on any other of the subjective quality-of-life measures from the QOLI or on the objective measures from this scale. The difference between groups in satisfaction with health remained significant when adjusting for smoking status and demographic variables, as shown in Table 2, and also when adjusting for each category of non-diabetes co-occurring medical illnesses (data not shown).
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TABLE 2. Ratings of Life Satisfaction From the Quality of Life Interview for Individuals With Serious Mental Illness, With and Without Type 2 Diabetes
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Health-Related Quality of Life
As compared with non-diabetic patients, those patients with diabetes had lower functional status as measured by the Physical composite score and the Mental composite score (Table 3). Patients with diabetes also had significantly lower scores, indicating more impairment, on subscales tapping perceived general health and mental health, physical functioning, role limitations due to physical health, role limitations due to emotional problems, bodily pain, social functioning, and mental health. There was no significant difference between groups on the Vitality subscale. When adjusting for smoking status and the demographic variables, all of the MOS SF–12 variables remained significantly different between groups except for the General Health subscale. When adjusting additionally for each of the categories of non-diabetes co-occurring medical illnesses, the significant differences between groups remained for the Physical and Mental Health composite scores and for the Physical Functioning, Role Limitations due to physical health, Role Limitations due to emotional problems, Social Functioning, and Mental Health subscales (data not shown).
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TABLE 3. Ratings of Health-Related Quality of Life From the Medical Outcomes Survey for Individuals With Serious Mental Illness, With and Without Type 2 Diabetes
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DISCUSSION
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In this sample of individuals with serious mental illness, individuals with diabetes, versus those without diabetes, reported worse health-related quality of life in physical and mental health domains, even beyond that accounted for by other somatic conditions. Patients with diabetes also reported less satisfaction with their health, but not with other life domains, suggesting that the diabetes-related decrements in quality of life have some specificity to health-related life satisfaction.
The most pronounced differences between the diabetes and the non-diabetes patients in health-related quality of life were found on the measures Physical Functioning (extent to which health limits physical activities such as moving a table, climbing flight of stairs, etc.); Role Limitations due to emotional problems (extent to which the person feels they have done less because of emotional problems); and Social Functioning (how much physical health or emotional problems interfere with social activities).
Our results are consistent with previous studies of individuals in the general population consistently showing that diabetes adversely affects health-related quality of life defined as persons’ sense of their own health and well-being.2–5 To our knowledge, our study is the first to extend this finding to persons with serious mental illness. Our results differ from some previous studies in the general population that have found differences between diabetes and non-diabetes samples in overall health-related functioning but not specifically in mental-health or social-functioning components.18–20 In contrast, we found large differences on the Mental Health and Social Functioning subscales of the Health-Related Quality of Life scale. This suggests that patients with diabetes and serious mental illness, whose mental health and social functioning are likely impaired by their psychiatric disorder, may be vulnerable to further decrements in these domains secondary to diabetes.
The vulnerability suggested by these findings underscores the importance of considering strategies to achieve primary and secondary prevention of diabetes and related, co-occurring medical problems among persons with serious mental illness. If our findings are replicated and diabetes is consistently shown to be linked to poorer quality of life and functioning, it would suggest that psychiatrists should consider carefully the risk/benefit issue of medications that cause metabolic abnormalities and increase the incidence of diabetes. The greater the adverse impact of diabetes, the more important it is for physicians to monitor patients who are at risk and to promote healthful behaviors such as exercise. For those patients who have both serious mental illness and type 2 diabetes, medical providers need to be attentive to the high burden of disease that these patients experience.
Our study was limited in that the diabetes and non-diabetes samples were not age-matched, and the diabetes sample was older; however, we adjusted for age in the multivariate comparisons. We were not able to adjust for all of the potentially confounding health-related variables that may affect quality of life. For example, obesity is associated with diabetes and may also adversely affect quality of life in persons with persistent psychiatric and medical illnesses, including diabetes.21–24 We also did not adjust for cognitive impairment or comorbid substance use; nor were we able to adjust for the severity of psychiatric symptoms, such as psychotic symptoms or depression. The observed differences between groups on the Mental Health subscale of the SF–12, which measures the degree to which the respondent feels "downhearted" or "calm," suggest that the diabetes group had reduced overall emotional well-being; this could partially account for the overall poorer health-related quality of life among the diabetes subgroup. However, it is noteworthy that the only observed differences on the QOLI satisfaction measures, which are typically correlated with depression, were in the area of satisfaction with health. Whether or not our diabetes and non-diabetes groups had different depression levels, our data suggest that the patients with diabetes consistently report reduced functioning due to both physical and mental problems. A logical implication of our study is that it is important to optimize treatment for depression in this population in order to minimize the potential impact of depression on functional status among persons with serious mental illness and diabetes.
Finally, our results do not enable us to know the mechanism by which diabetes contributes to reduced quality of life in serious mental illness because our quality-of-life measures were generic, and not diabetes-specific so as to allow for comparison with our non-diabetes sample. It is possible that patients with diabetes and serious mental illness experience increased neuropathy and pain secondary to their diabetes. It is also possible that metabolic adverse effects of antipsychotic medications worsen the diabetes illness and therefore contribute to further decrement in quality of life. These are important issues that should be the focus of future investigations.
Strengths of the study include the fact our sample is likely representative of those with serious mental illness and diabetes receiving care in community-based psychiatric clinics. Our results, therefore, may be generalizable to patients with serious mental illness receiving care in similar settings.
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ACKNOWLEDGMENTS
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This work was supported by Grant R01 MH 58717, (L. Dixon, P.I.), and a grant from the National Alliance for Research on Schizophrenia and Depression (L. Dixon, P.I.)
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REFERENCES
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- Centers for Disease Control and Prevention: National Center for Chronic Disease Prevention and Health Promotion: National Diabetes Surveillance System: Prevalence of Diabetes: Number (in Millions) of Persons With Diagnosed Diabetes, United States, 1980-2004; www.cdc.gov/diabetes/statistics/prev/national/figpersons.htm
- Polonsky WH: Emotional and quality-of-life aspects of diabetes management. Current Diabetes Reports 2002; 2:153–159[CrossRef][Medline]
- Rubin RR, Peyrot M: Quality of life and diabetes. Diabetes Metab Res Rev 1999; 15:205–218[Medline]
- Norris SL: Health-related quality of life among adults with diabetes. Current Diabetes Reports 2005; 5:124–130[CrossRef][Medline]
- Wandell PE: Quality of life of patients with diabetes mellitus: an overview of research in primary health care in the Nordic countries. Scand J Prim Health Care 2005; 23:68–74[CrossRef][Medline]
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ABSTRACT
INTRODUCTION
