According to a new study, being overweight or obese during middle age may increase the risk of certain dementias. The research is published in the May 3, 2011, print issue ofNeurology®, the medical journal of the American Academy of Neurology.

"Currently, 1.6 billion adults are overweight or obese worldwide and over 50 percent of adults in the United States and Europe fit into this category," said study author Weili Xu, MD, PhD, with the Karolinska Institutet in Stockholm, Sweden. "Our results contribute to the growing evidence that controlling body weight or losing weight in middle age could reduce your risk of dementia."

Researchers studied information from the Swedish Twin Registry on 8,534 twins age 65 or older. Of those, 350 were diagnosed with dementia and 114 had possible dementia. Information on participant's height and weight had been taken 30 years earlier.

Participants were grouped according to their body mass index (BMI), a measure of total body fat: underweight, normal weight, overweight and obese. Being overweight was defined as having a body mass index between 25 and 30 and obesity was defined as a body mass index of higher than 30. In the study, 2,541 twins, or nearly 30 percent, were either overweight or obese during middle age.

The study found that people who were overweight or obese at midlife had an 80 percent higher risk of developing dementia, Alzheimer's disease or vascular dementia in late life compared to people with normal BMI. The results remained the same after considering other factors, such as education, diabetes and vascular disease. A total of 26 percent of those with no dementia had been overweight in midlife, compared to 36 percent of those with questionable dementia and 39 percent of those with diagnosed dementia. Three percent of those with no dementia had been obese in midlife, compared to five percent of those with questionable dementia and seven percent of those with diagnosed dementia.

The researchers also analyzed the data in twin pairs where one twin had dementia and one twin did not and found that there was no longer a significant relationship between overweight and obesity and dementia in midlife. "This suggests that early life environmental factors and genetic factors may contribute to the link between midlife overweight and dementia," Xu said.

Source: American Academy of Neurology