Midlife diabetes diagnosis doubles dementia risk

A midlife diagnosis of diabetes increases the risk of developing Alzheimer’s disease and vascular dementia, based on results of a twin study including more than 13,000 individuals.

Previous studies have shown that people with diabetes are at increased risk for dementia, but little is known about the mechanism of action, the Karolinska Institute, Stockholm, and the Stockholm Gerontology Research Center conducted this twin study to examine the effect of diabetes on dementia and assess the possible role of genetics.

Data were taken from a national registry of Swedish twins who were at least 65 years old when they entered the study between 1998 and 2001. Of 13,693 study participants, 13,056 had no dementia, 467 had dementia, and 170 had questionable dementia, based on DSM-IV criteria. Midlife diabetes was defined as the onset of type 2 diabetes before age 65 years.

A total of 1,396 individuals had type 2 diabetes, 643 developed diabetes; 643 developed diabetes before age 65 years and 753 developed diabetes at age 65 years or older.

Overall, diabetes was significantly associated with an increased risk of dementia (increased risk of 63 percent), and patients whose diabetes was diagnosed at midlife were more than twice as likely to develop dementia as those diagnosed with diabetes later in life (increased risk of 176 percent), even after controlling for diabetes duration and twin factors.

In addition, data from co-twin matched case-control analyses showed that the effect of later-life diabetes diagnosis on dementia did not.

These data suggest that adult lifestyle traits such as diet, exercise, smoking and diabetes control may have a substantial impact on the link between midlife diabetes and dementia. But “unmeasured familial factors” including genetic factors and environmental influences in early life might contribute to the association between late-life diabetes diagnosis and dementia, the researchers noted.

The study’s limitations include the prevalence of dementia cases, the use of self-reports, and the lack of information about genes and environmental factors.