People diagnosed with type 2 diabetes face a risk of dementia 60 percent greater than that faced by people who do not have diabetes, a systematic analysis of published studies shows.
In addition, the risk is greater for women with diabetes than for men with the condition, the researchers say.
More than 2.3 million people and 100,000 dementia cases in 14 studies evaluating the link between diabetes and dementia were analyzed, more than seven times as much data looked at in previous reviews of the issue, they say.
The two most common forms of dementia include nonvascular dementia, mostly Alzheimer's disease, and vascular dementia, in which blood flow to the brain is affected and that was the focus of the study analysis.
A series of small strokes is the most common cause of vascular dementia, experts say.
The analysis found that the risk of such dementia is greater for women, the researchers report in the journal Diabetes Care.
"Diabetes increases the risk of developing dementia, but for a major subtype of dementia — namely vascular dementia, not Alzheimer's disease — the risk is higher in women with diabetes compared with men with diabetes," says study senior author Rachel Huxley, who heads Curtin University's School of Public Health in Perth, Australia.
The increased risk of vascular dementia in women may be because they are not treated as often as men for high blood pressure, which can be a factor in certain other health problems in addition to dementia, the researchers suggest.
"These findings add to the evidence that diabetes confers a greater vascular hazard in women compared with men," says Huxley. "Diabetes confers a greater risk of developing heart disease, stroke and now vascular dementia in women compared with men."
There is also a growing body of evidence that biology plays a part in the increased risk of diabetes-associated vascular dementia in women as compared with men, Huxley notes.
"More in-depth physiological studies are needed that examine how blood glucose interacts with the vasculature and whether there are any significant sex differences," she says.
A growing health issue, dementia affects around 44 million people around the world, the researchers note in their study, with 7.7 million additional cases diagnosed annually.
It is predicted the rate of dementia could double by 2030 and triple by the year 2050, they say.