The association was especially strong in people younger than 65. In that age group, “a quarter of the cases [of dementia] were attributed to depression and diabetes,” he said.
In Western populations, type 2 diabetes and major depression are increasingly common. And as many as 20 percent of people with diabetes, which is rapidly increasing in younger groups, also have depression, the researchers said in background notes with the study.
“To our knowledge, this is the first study to look at this issue in this way,” Davydow said. The findings were published online April 15 in JAMA Psychiatry.
The study points out a complicated link between depression, diabetes and dementia, but does not establish a direct cause-and-effect relationship.
“There is lots of evidence that those who struggle with depression are more likely to develop chronic medical problems like diabetes and heart disease and high blood pressure,” Davydow said.
“They are less likely to take medications if they are depressed. Those who have diabetes are more likely to suffer from depression,” he added.
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Moreover, diabetes makes it more likely that plaque will develop in blood vessels, which can lead to strokes and dementia, Davydow said.