Type 2 diabetes mellitus and cognition: an understudied issue in women's health

Diabetes is a common chronic illness, affecting approximately 16 million Americans, and is slightly more common in women than men. Data from population studies demonstrate that women with diabetes are at greater risk for cardiovascular disease, the leading cause of death among women and an independent risk factor for cognitive decline. Longitudinal epidemiologic studies report an association between diabetes mellitus and vascular dementia, but conflicting data on the association between diabetes and Alzheimer's dementia. Whether type 2 diabetes has an effect on cognitive function, independent of dementia, has received much attention since the 1980s, but the question remains unresolved.

The literature was rigorously reviewed for studies in which cognitive functioning was measured with neuropsychological (NP) tests in participants with type 2 diabetes and a control/comparison group without diabetes.

Of 32 studies that reported the effects of type 2 diabetes on cognition in nondemented middle-aged and older adults, 30 included women in their samples, and two focused exclusively on women. Of studies that included women, 20 (67%) reported that participants with type 2 diabetes performed more poorly than those without diabetics on one or more NP tests, leading the authors to conclude that diabetes is positively associated with cognitive dysfunction.

Owing to the small number of studies with adequate numbers of women to report findings by gender, little is known about the effect of type 2 diabetes on cognition in women. It is critical that studies on type 2 diabetes and cognitive functioning be designed to include women in numbers adequate for examination of gender effects. The discussion addresses issues specific to women that warrant further research.