The Framingham study is a large prospective study of over 5,000 men and women living in Framingham, Massachusetts who have been followed every 2 years since 1948. Data from it is used to estimate risk of heart and other diseases. The dementia part of the study began in 1975 using several neuropsychological tests. Recent data from the study reports that people who participate in moderate to heavy physical activity have a 45% lower risk for dementia over time.

"A reduced risk of dementia may be one of the additional health benefits that can actually be derived from maintaining at least moderate physical activity," lead author Zaldy Tan, MD, MPH, from the Brigham and Women's Hospital, VA Boston, and Harvard Medical School, in Massachusetts, concluded. Dr. Tan presented the results at the Alzheimer's Association International Conference on Alzheimer's Disease 2010.

Previous findings from the Framingham have already shown moderate or high physical activity to be associated with a number of positive outcomes, including a reduced risk for stroke and cardiovascular disease, higher high-density lipoprotein cholesterol levels, a reduced risk for colon cancer, and lower overall rates of mortality.

Physical activity is a potential preventive factor that would likely take years to manifest its effect, "so the fact that we've followed them for over 20 years, this is something that suggests that long-term physical activity actually works," Dr. Tan noted. The mechanism is not clear, he added, but reduction of cardiovascular risk factors such as hypertension, or the release of neurotrophic factors, are possible effects.

The Framingham study is not the only one to demonstrate this relationship. A recent review showed that 20 of 24 population-based studies showed a link between physical activity and reduced risk for dementia or cognitive decline. The flip side of this is that four of those studies did not support the correlation. However, the Framingham study is one of the best because it has such well designed, long-term follow-up.