Adults who have both diabetes and major depression are more than twice as likely to develop dementia, compared to adults with diabetes only, according to a study published in the recent Journal of General Internal Medicine.
Dementia is the progressive decline of thinking and reasoning abilities. These can include memory loss, difficulty with basic math, wandering, living in the past, personality changes, and not recognizing familiar people.
"Diabetes alone has shown to be a risk factor for dementia, as has major depression by itself," noted the lead author of the study, Dr. Wayne Katon, University of Washington (UW) professor of psychiatry and behavioral sciences. Also on the study team were researchers from the Group Health Research Institute in Seattle and the Veterans Affairs (VA) Puget Sound Health Care System, as well as UW researchers in medicine and in epidemiology.
Various other population studies, Katon and the other authors noted, have shown that the risk of Alzheimer's disease, vascular dementia, and other types of dementia is from 40 percent to 100 percent higher in people with diabetes, compared to people without diabetes. A history of depression more than doubles the subsequent risk of Alzheimer's disease and other forms of dementia in the general population.
"We wanted to determine the effects of both conditions - diabetes and major depression--occurring together," Katon said. "Our analysis suggests that major depression more than doubles the risk of dementia in adults with diabetes."
The research team on this project, which is part of the Pathways Epidemiological Follow-Up Study, tracked the outcomes of adults from the Group Health Cooperative's diabetes registry who agreed to participate. They were patients from nine Puget Sound area primary-care clinics in western Washington state. The clinics were chosen for their socioeconomic and racial/ethnic diversity and were demographically similar to the area's population. Initial enrollment of patients took place between 2000 and 2002, and the patients were studied for five years. Patients already diagnosed with dementia were excluded from the study.
Over the five-year period, 36 of 455, or 7.9 percent, of the diabetes patients with major depression were diagnosed with dementia. Among the 3,382 patients with diabetes alone, 163 or 4.8 percent developed dementia.
The researchers calculated that major depression with diabetes was associated with a 2.7-fold increase of dementia, compared to diabetes alone. Because the onset of dementia can sometimes be marked by depression, the researchers also adjusted their hazard model to exclude patients who developed dementia in the first two years after their depression diagnosis.
The team's previous findings from earlier studies showed that depression increases the mortality rate among people with diabetes, as well as the rate of complications such as heart, blood vessel, kidney and vision problems.