Doing your best to keep the extra pounds off during middle age may not only keep your body healthy, but your mind fit, too. A new study shows that being severely overweight well before your senior years may have a deteriorating impact on your mind.

While the health consequences of excess weight in terms of vascular disease and joint pain are well documented, for the first time, researchers appear to have found a direct link between obesity, dementia and Alzheimer’s disease.

"Obesity at midlife may increase the risk of dementia and Alzheimer’s disease later in life." noted the study authors.

Moreover, if one’s obesity is coupled with high blood pressure and elevated cholesterol, as it often is, the risk for Alzheimer’s is six times greater than that of a healthy individual.

For the study, published in October 2005 in the Archives of Neurology, researchers from the Karolinska Institute in Sweden recruited 1,449 middle-aged men and women and measured the participants’ body mass index (BMI), blood pressure and cholesterol levels. Approximately 20 years later, a follow-up exam was given in which the participants’ cognitive abilities were measured.

The researchers found that almost 17 percent of those who were obese at middle age—defined by a BMI greater than 30—developed either Alzheimer’s disease or dementia, compared to 5 percent who were of normal weight for their height. After taking other risk factors like high blood pressure and high cholesterol into account, the risk of future mental decline was still twice as high from being overweight alone. There was no notable difference in risk between men and women.

The researchers explain that while the mechanism is not entirely understood, the vascular problems associated with high blood pressure and cholesterol may affect the brain’s ability to function. So, controlling these factors may help.

"Elimination of even one risk factor can decrease this risk [for dementia]." writes lead study author, Dr. Miia Kivipelto of the Aging Research Center at the Karolinska Institute.

More research is needed to determine why obesity alone increases the risk of mental decline, but in the meantime, the researchers suggest that shedding excess pounds and maintaining a healthy weight may allow you to keep your mind going strong late into life.