Depression and diabetes are two conditions that are often linked, but the exact relationship between them is still not fully understood. A recent meta-analysis of nine cohort studies found that adults with depression had a 37% higher risk of developing type 2 diabetes after considering factors common to both disorders, such as sex, body mass index, and poverty. The incidence of depression is two to three times higher in people with diabetes mellitus, and most cases remain underdiagnosed. The purpose of this review was to show the links between depression and diabetes, to point out the importance of identifying depression in diabetic patients, and to identify possible ways to address both diseases.
Possible common pathophysiological mechanisms such as stress and inflammation were explained, while emphasis was placed on detecting depression in diabetic patients. An important aspect for the diabetes specialist would be the understanding of the common origins of diabetes and depression and awareness of this fairly common comorbidity, in order to improve the outcomes of both diseases. There are several potential mechanisms at play in this observed relationship. Depression itself may contribute to diabetes.
For example, people with depression are more likely to have changes in body weight and are less likely to engage in healthy behaviors, such as exercise, which increases the risk of developing diabetes. Alternatively, many of the medications used to treat depression cause weight gain and sedation, such as tricyclic antidepressants and selective serotonin reuptake inhibitors, which may also contribute to the development of diabetes. In any case, the onset of depression or its treatment may unmask a tendency to develop diabetes, perhaps earlier than it would otherwise have manifested itself. People who were ≥51 years of age may have already passed the period of highest risk of developing diabetes, so a previous history of depression did not alter the risk of developing diabetes later.
That is, having depressive episodes can accelerate the onset of diabetes in people at risk. A recent report of higher rates of depression in people with impaired glucose tolerance supports this idea. Research has found that people suffering from diabetes and depression have poorer metabolic and glycemic control, which, in turn, has been found to intensify symptoms of depression. It is possible that the demands of managing a chronic disease, such as type 2 diabetes, can lead to depression.
Studies have shown that people with depression have a higher risk of complications from diabetes, but it has not been determined whether depression increases the risk of complications or vice versa. The gender gap in depression is a well-published finding; however, age-related changes in the risk of depression and the impact of diabetes have not been sufficiently investigated so far. Of the 65,381 women aged 50 to 75 in 1996 who participated in the study, 2,844 women were newly diagnosed with type 2 diabetes and 7,415 women developed depression in the following 10 years. Initially, the unadjusted OR and the 95% CI of the association between depression and new-onset diabetes were estimated by simple logistic regression, with the status of the case-control subject as a dependent variable and a history of previous depressive episodes as the main independent variable. For example, a person with depression may be more likely to undergo clinical tests such as a random or fasting blood glucose level at the time of diagnosis of depression compared to someone without medical illness, increasing the likelihood of being diagnosed with diabetes. Research suggests a bidirectional relationship between these two disease states; in which the incidence of depression increases in patients with diabetes and the incidence of diabetes (specifically DM2) increases in patients with depression. In summary, it's clear that diabetes and depression are important comorbid conditions; comorbid depression is associated with poorer outcomes in people with diabetes.
The temporal relationship has important implications for the mechanisms by which depression could predispose to diabetes and for controlling diabetes risk in people diagnosed with depression.