A new study published in the May 19, 2009, print issue of Neurology shows that older people who are thinner or are losing weight quickly are at a higher risk of developing dementia, especially if they started out overweight or obese.

For the study, researchers followed for eight years 1,836 Japanese Americans in Washington state with an average age of 72. During that time, 129 people developed dementia.

The research found that people with lower body mass index (BMI) scores at the beginning of the study were 79 percent more likely to develop dementia than those with higher BMI scores.

In addition, those who lost weight over the study period at a faster rate were nearly three times more likely to develop dementia than those who lost weight more slowly over time. This result was more pronounced in those who were overweight or obese to start; those with a BMI of 23 or higher had an 82-percent reduced risk of developing the disease compared to those who were normal or underweight. The results were the same after testing for other health risk factors such as smoking, exercise and gender.

"Our finding suggests that losing weight quickly in older age may be an early sign of dementia," said study author Tiffany Hughes, Ph.D., MPH, who is with the University of Pittsburgh School of Medicine but conducted the research while she was a doctoral student at the University of South Florida. "This doesn't mean that being obese or overweight is healthy for the mind or body, but losing weight may be a sign of emerging brain disease."

Hughes says other current research shows that, in contrast, a larger belly in midlife may be a risk factor for dementia.

"Dementia has been shown to develop in the brain decades before any symptoms develop," Hughes said. "These findings likely reflect that process. In middle age, obesity may be a risk factor for dementia, while declining weight in late life may be considered one of the first changes from the disease that occurs before it actually affects a person's memory."