The Interrelationship between Diabetes and Depression

Both diabetes and depression are highly prevalent health problems that have a negative impact on various aspects of health, quality of life, and mortality. It has been well documented that depression is more common among people with diabetes than among the general population. Although the exact nature of the relationship between diabetes and depression is not fully understood, the bidirectional relationship of these two diseases has been suggested.1) A meta-analysis by Mezuk et al.2) showed that depression is associated with a 60% increased risk of type 2 diabetes and type 2 diabetes is associated with 15% increased risk of depression. Depression is associated with biochemical changes including increased activity of counter-regulatory hormones, altered glucose transport function, and increased production of proinflammatory cytokines, which contribute to insulin resistance, beta islet cell dysfunction, and ultimately diabetes. Depression is also associated with unhealthy behaviors including smoking, physical inactivity, and hypercaloric diets, which are risk factors for the development of diabetes. In patients with diabetes, the psychosocial burden of having a chronic illness may result in development of depression.3,4) Comorbid depression in patients with diabetes is related to poor glycemic control, higher severity of diabetic complications, increased risk of cardiovascular diseases, higher functional disability, and higher all-cause mortality.5)

In the present issue, Sung et al.6) investigated the relationship between diabetes and depressive symptoms among Korean women using a nationally representative data of Korean. They obtained the data from the fifth Korea National Health and Nutrition Examination survey 2010-2011, which consisted of 6,572 Korean women aged 30 years and over. They found that diabetes has a relationship with depressive symptoms but that patients with diabetes were less likely to be treated for their depression.

The result that women with diabetes have a higher likelihood of having depressive symptoms is consistent with findings from previous research. However, the authors report that there is a lack of prior research on the treatment of depression in individuals with diabetes. Gill et al.7) investigated the prescription of antidepressant medications for patients with medical comorbidities including diabetes in the primary care setting using electronic health record data. They found that primary care physicians prescribed antidepressant medication less aggressively for patients with multiple comorbidities, although there was no significant difference in the antidepressant medication prescription for diabetes alone. Patients with medical comorbidities may be already taking multiple medications for management of comorbid medical diseases so additional medications may increase their burden in relation to potential side effects and cost. Low rates of depression treatment in patients with diabetes may be related to a concern about the adverse metabolic effects of antidepressant medication.8)

However, Sung et al.'s study is a cross-sectional design which does not prove causality. Although they described that diabetes is associated with an increased risk of depressive symptoms, the direction of relationship between diabetes and depressive symptoms was unclear. One limitation of this study was that depressive symptoms were assessed by the Patient Health Questionnaire-2 with low specificity, not by a formal depression diagnostic interview.

The comorbidity of diabetes and depression is associated with significantly higher morbidity, disability, and mortality beyond those due to either diabetes or depression alone.9) Sung et al.6)'s study suggests that diabetes and depression frequently exist together and there is a possibility that depression treatment is suboptimal in patients with diabetes. Therefore, it should be emphasized that the coordinated care system which optimizes diagnosis and treatment of depression in patients with diabetes is necessary.