The exact manner in which diabetes and depression interact to result in poorer outcomes is not certain. Some studies suggest that a genetic marker for dementia is associated with a faster cognitive decline. Depression may also raise the risk of dementia, the authors noted, because of biological abnormalities linked to this affective illness, including high levels of the stress hormone cortisol, poor regulation in the hypothalamus-pituitary system, or autonomic nervous system problems that can affect heart rate, blood clotting, and inflammatory responses.

Depression, they added, might also raise the risk of dementia because of behaviors common in the condition, such as smoking, over-eating, lack of exercise, and difficulty in adhering to medication and treatment regimens. In the current study, patients with both diabetes and major depression were more likely to be female, single, smokers, physically inactive, and treated with insulin. They also had more diabetes complications and a higher body mass index, a ratio calculated from height and weight. However, these differences were controlled for in the analysis and depression remained an important risk factor.

Diabetes, the authors noted, is a risk factor for dementia because of blood vessel problems and also may accelerate the decline of Alzheimer's disease. Many factors linked to diabetes might also increase the odds of developing dementia, including tissue damage from high blood sugar levels, episodes of low blood sugar and insulin resistance.

Depression is common among people who have diabetes. Until more research is available on the exact mechanisms behind the links between depression, diabetes, and dementia, the researchers say, "It seems prudent for clinicians to add effective screening and treatment for depression to other preventive measures such as exercise, weight control, and blood sugar control to protect against the development of cognitive deficits in patients with diabetes."

Source: University of Washington