From the research article in Archives of Neurology, October 2005.

Aside from the well-documented ill effects of obesity, new evidence documents a link between middle age obesity and a decline in mental acuity in later years. It has long been established that vascular health, cardiac fitness, joint health, and endocrinological health are directly affected by weight gain and obesity, but a study published in the October 2005 Archives of Neurology links obesity with dementia and Alzheimer's disease.

The study was performed by the Karolinska Institute in Sweden . The institute recruited 1,449 middle-aged men and women and measured their BMI (body mass index), cholesterol levels, and blood pressure. These participants were examined 20 years later and evaluated for cognitive (mental agility) abilities.

These researchers found that 17% of those who where obese at middle age (obesity was defined has having a BMI greater than 30) developed dementia or where diagnosed with Alzheimer's disease. This compared with a 5% dementia/Alzheimer's rate in those of normal weight. Even when the co-morbidity (contributing) factors of high cholesterol and high blood pressure were factored out, those who were overweight were still twice as likely to develop Alzheimer's or dementia. There was no significant difference between men and women.

While the mechanism for these findings is unknown, and the researchers acknowledge that further research is warranted, this study should provide additional motivation for those contemplating losing weight.