A new joint US and Canadian observational study has found that depression is linked to accelerated cognitive decline in patients with type 2 diabetes. According to the American Diabetes Association, studies have shown that people with diabetes have a greater risk of depression than people without diabetes but scientists still do not know why this is the case.
The researchers therefore wanted to investigate whether or not depression in patients with type 2 diabetes will accelerate cognitive decline. In the new study 2,977 study participants with type 2 diabetes at high risk for cardiovascular events participated in the 40-month cohort ACCORD-MIND (Action to Control Cardiovascular Risk in Diabetes-Memory in Diabetes) study. Of these, 2764 people completed the 20-month cognitive assessment and 2664 people completed the 40-month cognitive assessment. The study participants were middle-aged and older adults who had type 2 diabetes for a mean duration of 9 years and who were at high risk for cardiovascular disease.
In the study, the 9-item Patient Health Questionnaire or PHQ-9 test was used to assess the severity of depression. Study participants were considered to be depressed if they scored a 10 or higher on the PHQ-9 test. At baseline assessment, 18% of the study participants scored 10 or greater on the PHQ-9 test, compared with 17% at 20 months and 16% at 40 months.
One of the co-authors of the study was Mark Sullivan, MD, PhD, of the University of Washington in Seattle. Dr. Sullivan and his colleagues found that over the 40 months of follow-up, those study participants found to be depressed, showed the greatest cognitive decline on their Digit Symbol Substitution Test (DSST) at the end of the study. The DSST a well established psychological test that measures general cognitive performance.
Since no patients had dementia at the beginning of the study, the study findings suggest that depression is not simply an early manifestation of dementia but is a risk factor for cognitive decline in patients with type 2 diabetes.
The study's conclusion was that "depression in patients with type 2 diabetes was associated with greater cognitive decline in all domains, across all treatment arms, and in all participant subgroups assessed."
The researchers noted there was one important limitation of their study : since their study did not involve patients without diabetes, they were therefore not able to estimate the strength of the depression-cognitive decline association in nondiabetic patients.
