An ongoing study on twins appears to show that diabetics have a significantly increased risk of both Alzheimer's and other forms of dementia.
It also suggests that the risk of dementia is especially strong if the onset of diabetes occurs in middle age.
"Our results . . . highlighted the need to maintain a healthy lifestyle during adulthood in order to reduce the risk of dementia late in life," said Dr. Margaret Gatz, who directs the Study of Dementia in Swedish Twins.
Gatz and colleagues from Sweden have found that getting diabetes before the age of 65 corresponds to a 125 percent increased risk for Alzheimer's disease.
Revealing their findings in the journal Diabetes, the researchers said that the risk of Alzheimer's disease or other dementia was significant for mid-life diabetics - as opposed to those who develop diabetes after 65 - even when controlling for family factors.
Other studies conducted in the past showed genetic factors and childhood poverty to independently contribute to the risk of both diabetes and dementia.
"Twins provide naturally matched pairs, in which confounding factors such as genetics and childhood environment may be removed when comparisons are made between twins," said Gatz, professor of psychology, gerontology and preventive medicine at the University of Southern California and foreign adjunct professor of medical epidemiology and biostatistics at the Karolinska Institute in Sweden.
In their study report, the researchers write that the chances of a diabetic developing Alzheimer's disease may be even greater in real life than in the study.
They say that they have identified some factors that might have led them to underestimate the risk of dementia and Alzheimer's among those who develop diabetes before the age of 65.
Given that diabetes usually appears at a younger age than dementia does, and is also associated with a higher mortality rate, the researchers say that the size of the sample of older adults might have been reduced.
Besides that, add the researchers, about 30 percent of older adults with diabetes have not been diagnosed.
The team say that their findings implicate adult choices such as exercise, diet and smoking, as well as glycemic control in patients with diabetes, in affecting risk for Alzheimer's disease and diabetes.
The sample for the study was 13,693 Swedish twins aged 65 or older in 1998, the year tracking for dementia began.
Information about diabetes came from prior surveys of twins and linkage to hospital discharge registry data beginning in the 1960s.