Weight loss can be a sign that a woman will develop dementia in the future, US researchers have discovered.
In a study of over 1,000 people, women who later developed dementia had a drop in weight as early as a decade prior to the onset of memory loss.
The Mayo Clinic team do not think their finding will help doctors spot early dementia but say it could shed light on the brain mechanisms dementia affects.
They presented their work at an Alzheimer's conference in Spain.
The researchers identified 560 people who were diagnosed with dementia between 1990 and 1994. They then found a group of people of similar age who did not have dementia.
They looked back at the weight of all of the patients over the preceding 30 years.
Among the women in the study, those who later developed dementia started off at the same weight as those who did not develop dementia, but then their weight drifted downward by a few pounds 10 years before the developed any dementia symptoms.
The weight of these women also went downward a few more pounds when the memory loss first manifested.
Lead researcher Dr David Knopman said: "The weight of those women who developed dementia was drifting downward many years before the onset of symptoms.
"This illustrates changes that occur before the memory loss and mental decline in dementia.
"We believe that the brain disease began to interfere somehow with maintenance of body weight, long before it affected memory and thinking."
He said there were several possible explanations for how this might occur.
It might be that the disease processes that cause dementia also have an effect on initiative and therefore the women lose interest in eating.
Alternatively, women with imminent dementia might develop a duller sense of smell or taste.
"Or they might experience an earlier sense of satiety - feeling full."
Dr Knopman said it was possible the weight loss could have something to do with hormonal changes around the time of menopause because they did not find the same trend among the men that they studied.
However, a study reported in the Archives of Neurology in January 2005 found men who later developed dementia experienced weight loss up to six years before diagnosis.
The UK authors of this study, Dr Robert Stewart and colleagues from the Institute of Psychiatry, London, said: "An important consideration arising from research in this area is the extent to which weight loss may be prevented or minimised in dementia.
"Poor nutrition and frailty frequently complicate later stages of dementia, causing falls, poor wound healing, and increased physical dependence."
Past studies have suggested that dietary interventions may prevent weight loss in patients with Alzheimer's disease and may delay cognitive decline and mortality.
Rebecca Wood, chief executive of the Alzheimer's Research Trust, said: "These findings need to be take further urgently as they may reveal how dementia develops and therefore provide routes to the new treatments we so desperately need."
She added: "The difference in men and women suggested by this latest research suggests it could be linked to post-menopausal hormone changes.
"This is interesting as low oestrogen levels in women have been shown to increase the risk of dementia."
Dr Susanne Sorensen, of the Alzheimer's Society, said: "The observed weight loss is interesting as it could indicate the part of the brain responsible for weight loss is also one of the first to be damaged by the disease.
"Further research is now needed to identify what causes this weight loss."