Rapid weight loss may be a warning sign
Researchers have produced more evidence that rapid weight loss in old age may be a early warning sign of dementia.
The University of South Florida study suggests the risk of dementia appears to be particularly high if the person started out overweight or obese.
The eight-year study, based on 1,836 Japanese Americans, appears in the journal Neurology.
It found people who were thin, or lost weight quickly seemed to be at highest risk of developing dementia.
BODY MASS INDEX
Calculated by dividing weight in kilograms by height in metres squared
Normal: 18.5 - 24.9
Overweight: 25 - 29.9
Obese: Above 30
People with a lower body mass index (BMI) at the beginning of the study were 79% more likely to develop dementia than those who carried more weight.
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 - people with a BMI of 23 or higher had an 82% reduced risk of developing the disease compared to those whose BMI was lower.
The findings echo a study published in 2006 which found women who later developed dementia had a drop in weight as early as a decade prior to the onset of memory loss.
Lead researcher Dr Tiffany Hughes said there was growing evidence that declining weight in later life may be one of the first physical changes from the disease that occur before it actually affects memory.
She said: "Our finding suggests that losing weight quickly in older age may be an early sign of dementia."
However, she also stressed that the research did not suggest that being obese or overweight was a way to protect against dementia.
In fact, previous research has shown that carrying excess weight around the stomach in middle age may increase the risk of the disease.
Rebecca Wood, of the Alzheimer's Research Trust, said: "Sudden weight loss may be an early sign of dementia, and is cause to see a GP.
"However, obesity is not desirable; in middle age, being overweight can increase dementia risk.
"The best way to reduce dementia risk is to maintain a balanced diet, regular exercise and frequent social interactions.
"Much more research like this is needed if we are to improve support for people with dementia: a condition that remains undiagnosed in most cases."