Older people who rapidly lose weight could be at higher risk of developing dementia, according to an American study.

The findings appeared in the May 2009 issue of Neurology, the journal of the American Academy of Neurology.

The research was based on a population-based prospective cohort study of 1800 older Japanese-Americans in the state of Washington which ran from 1992 to 2001.

At the start of the study, none of the participants had dementia but by 2001, 129 participants had developed it.

An analysis of the study found that the older people who had a higher body mass index at the start of the project were much less likely to develop Alzheimer’s disease.

However the people with the greatest risk of developing dementia were those who experienced a sudden decline in BMI, particularly if they had been obese to start with.

The researchers, from the University of Pittsburgh, the University of South Florida and the University of Washington, concluded that the rapid loss of weight in later life may be “preclinical indicators” of an underlying dementing illness.

Other research suggests that obesity among middle-aged people may be a risk factor for dementia.