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, a new study by researchers at the University of Pittsburgh, the University of South Florida and the University of Washington found.

The research is published in the May 19, 2009, print issue of Neurology, the medical journal of the American Academy of Neurology.

For the study, researchers followed for eight years 1,836 Japanese Americans in Washington state from the Kame Project in Seattle. The average age of the study participants was 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, PhD, MPH, who is now with the University of Pittsburgh School of Medicine but conducted the research while she was a dual degree doctoral student in Aging Studies and master’s student in public health (epidemiology) 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.”

Dr. 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,” Dr. 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.”

The mechanisms for why weight loss may increase risk for dementia in late life are unknown, said study co-author Amy Borenstein, PhD, a professor at the USF College of Public Health. “But, it’s possible that brain areas that control weight are affected before people develop cognitive symptoms.”

Dr. Borenstein was the co-principal investigator for the Kame Project in Seattle before joining USF. She has drawn upon data from the large-scale prospective study for other research, including an earlier study showing that antioxidants abundant in fruit and vegetable juices may play an important role in reducing the risk of Alzheimer’s disease.

Other USF College of Public Health collaborators on the study were Yougui Wu, PhD, assistant professor in the Department of Epidemiology and Biostatistics, and Elizabeth Schofield, a doctoral student in biostatistics.