Although there are no large studies indicating that depression treatments for DM/D patients improve medical outcomes, studies by Lustman and colleagues suggest that the treatments may have this important effect. In their CBT study,27 these investigators found that patients receiving CBT had substantially better HbA1C levels 6 months after the intervention than did control patients (9.5% vs 10.9%; P = .03).
Despite the potential efficacy of depression treatment, DM/D patients are likely to experience significant gaps in their depression care. Providers often fail to detect depression among their patients,8,28,29 and when depression is identified, depression-specific therapies often are not initiated.28 Primary care physicians may be uncomfortable managing depression because they lack treatment expertise or because of time constraints and competing clinical demands. Patients may be unwilling to accept or continue antidepressant treatment because of concerns about stigma or side effects.30 Effective CBT therapy often is unavailable because of the lack of adequately trained therapists or limitations on patients’ mental health benefits.31,32 Among patients who initiate a course of antidepressant medication, long-term adherence is poor. In a large managed care organization, 28% of patients discontinued their antidepressants within the first month of treatment and 44% discontinued these medications by the third month.33 Pharmaceutical claims databases suggest that 30% of patients with private insurance and 70% of patients with Medicaid coverage fill fewer than 4 30-day prescriptions in the 6 months after initiation of antidepressant therapy and thus do not receive an adequate antidepressant trial.34,35
A potential barrier to effective depression management among diabetes patients is the lack of a coherent view of patients’ clinical problems that encompasses both disorders. At the system level, this often is reflected by a structural lack of integration between medical and mental health services, with mental health and general medical providers often treating patients in different locations, maintaining separate medical records, and communicating infrequently.36,37 Primary care providers often do not appreciate the importance of aggressive depression management for patients’ overall health, and patients often do not draw connections between their depressive symptoms and their ability to manage their diabetes. Despite a good deal of descriptive epidemiology about the confluence of diabetes and depression as well as the availability of effective treatments, there is little consensus regarding the mechanisms linking these 2 conditions or how the care of DM/D patients might be most effectively managed.
CONCEPTUAL FRAMEWORK FOR THE RELATIONSHIP BETWEEN DIABETES AND DEPRESSION
Based on an extensive review of the literature, we developed a framework for better understanding the impact of depression on diabetes care and treatment outcomes in managed care settings (Figure). This model specifies 4 main pathways through which depression may affect outcomes among patients with DM/D: 1) by directly impacting their health-related quality of life, 2) by affecting their physical activity levels, 3) by affecting their self efficacy for diabetes management and self care, and 4) by affecting their ability to communicate effectively with healthcare providers. The Figure also suggests the theoretical impact of treatment with antidepressants or behaviorally focused counseling such as CBT.
First Pathway: Depression Directly Affects DM/D Patients’ Quality of Life and Functioning
Depression directly affects the health-related quality of life of patients with many chronic disorders, including diabetes.20,38 Depression is associated with increased mortality rates among patients with heart failure,39 MI,40 and stroke.41 Physical, social, and role functioning are compromised more by depressive symptoms than by most other chronic medical conditions, including hypertension, chronic lung diseases, gastrointestinal conditions, and arthritis.42,43 Patients who have both depression and a comorbid medical condition, including patients with DM/D, experience additive disability.44 Thus, addressing depressive symptoms among DM/D patients is likely to improve their health-related quality of life, even if diabetes-related pathophysiology and outcomes remain unchanged.
Second Pathway: Depression Affects DM/D Patients’ Level of Physical Activity
Diabetes patients who are depressed are more likely to report limited physical functioning,17,45 and increasing physical activity may be one of the most important behavioral changes for DM/D patients. Epidemiologic studies have repeatedly found cross-sectional associations between low levels of physical activity, diabetes, and depression.46,47 Longitudinal studies indicate that patients who are more physically active have better diabetesrelated outcomes, and most studies indicate that individuals who are less physically active are more likely to develop depression.46,48,49 In a prospective study, Lampinen and colleagues found that subjects who decreased their level of physical activity over time were particularly prone to depression.50