The Comorbidity of Diabetes Mellitus and Depression

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Abstract

Several factors, including sedentary lifestyle, obesity, and an aging population, contribute to epidemic rates of type 2 diabetes mellitus. Depression frequently occurs comorbidly with diabetes although it is unrecognized and untreated in approximately two thirds of patients with both conditions. The course of depression in patients with both diabetes and depression is chronic and severe. Up to 80% of patients with diabetes and depression will experience a relapse of depressive symptoms over a 5-year period. Depression is associated with nonadherence to diabetes self-care—including following dietary restrictions, medication compliance, and blood glucose monitoring—resulting in worse overall clinical outcomes. Due to potential negative health consequences associated with comorbid diabetes and depression, both conditions should be optimally treated to maximize patient outcomes.

Section snippets

Prevalence

The reported prevalence of depression in patients with diabetes varies widely, a fact that may be accounted for by methodologic differences and limitations of existing epidemiologic studies. Factors such as inclusion of patients without distinguishing between type 1 and type 2 diabetes, self-reported depressive symptoms versus clinically diagnosed depression, and lack of documentation regarding relevant factors associated with the disease state (e.g., number of diabetes complications, other

The relation between diabetes and depression

There is growing evidence regarding the bidirectional adverse interaction between diabetes and depression. A longitudinal study found that depressive symptoms at baseline were associated with an increased incidence of type 2 diabetes at follow-up over a 3-year period; an increased risk for developing depressive symptoms over the 3-year period was associated with treated type 2 diabetes, but conversely baseline impaired fasting glucose and untreated type 2 diabetes were associated with reduced

Depression assessment

Assessing symptoms of depression is not as difficult in patients with diabetes as it is in patients with certain other medical comorbidities. In spite of some overlap between depression and physiologic diabetes symptoms, depression screening tools (e.g., Beck Depression Inventory [BDI]41), the Center for Epidemiologic Studies Depression Scale (CES-D),42 and case-finding instruments (e.g., Patient Health Questionnaire [PHQ]–943) appear to retain sensitivity and validity in this comorbid

Clinical trials

Several controlled and open-label studies have evaluated the effects of antidepressant treatment in patients with diabetes. A retrospective study reported that only 31% of patients with comorbid diabetes and depression received adequate antidepressant treatment and only 6.7% received four or more sessions of outpatient psychotherapy visits during a 12-month period.45 This nominal treatment level suggests that more effective management of depression in patients with diabetes is imperative.

An

Quality of care for patients with comorbid diabetes mellitus and depression

Even though depressive symptoms severe enough to warrant treatment are found in 1 of 4 patients with diabetes,6 adequate treatment of the affective component of this comorbidity is lacking. Because the majority of patients with diabetes and MDD are treated in the primary care setting,31 suitable intervention in this treatment environment is essential. The Pathways Study,56 a population-based epidemiologic investigation, included an evaluation of the comparative effectiveness of collaborative

Healthcare costs related to comorbid diabetes and depression

Regardless of the temporal and causative influences that depression and diabetes exert on each other, there remains no doubt that patients with these comorbid disorders incur higher healthcare costs than nondepressed patients with diabetes. A study comparing healthcare costs in patients with diabetes who were divided into high, medium, or low tertiles based on depression severity found that healthcare costs increased as depression severity increased.33 Patients with highly severe depression,

Summary

Approximately 200 million people worldwide and 21 million Americans have diabetes,23 with an estimated worldwide increase to 333 million by 2025 if steps are not taken to slow the epidemic advance of the disease.63 The risk for developing MDD increases from 2.8% for people without existing medical conditions to 4.0% in patients with ≥1 long-term medical condition.64 Conversely, depressed adults have a 37% increased risk of developing type 2 diabetes.23 Depression imparts a serious deleterious

Author disclosures

The author of this article has disclosed the following industry relationships:

Wayne J. Katon, MD, has served on an advisory board for Eli Lilly & Co.; and has received honoraria from Eli Lilly & Co., Forest Laboratories, Inc., Pfizer Inc, and Wyeth.

Acknowledgment

I thank Carol Dyer, MS, of Prescott Medical Communications Group for manuscript preparation assistance.

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