In a recent study, researchers tracked rates of dementia and diabetes in twins, and discovered that developing type 2 diabetes before the age of 65 was associated with an 125 percent increased risk of subsequently developing Alzheimer’s disease.
Various studies have begun to show that vascular risk factors are important not only for increasing risk of vascular dementia, but also for increasing risk of Alzheimer’s disease. But this means that people could potentially reduce their risk of Alzheimer’s disease by attending to the kinds of health behaviors that reduce vascular risk -- such as controlling blood pressure, cholesterol and diabetes.
One surprising discovery of the twins study was that diabetes that first occurred before age 65 was a far more important risk factor for dementia than diabetes that occurred later. This means that, while it is possible that long-term diabetes could cause some sort of damage to the brain, it is also possible that diabetes and dementia each arise from the same environmental exposures and influences.
New York Times February 4, 2009