The researchers examined the records of 481 people with dementia and compared them to 481 people of the same age and gender who did not have dementia. The average weight was the same for those in the two groups from 21 to 30 years before the year the disease was diagnosed. But the women who would later develop dementia started losing weight up to 20 years before the disease was diagnosed. On average, those with dementia weighed 12 pounds less than those without the disease the year the disease was diagnosed.
"One explanation for the weight loss is that, in the very early stages of dementia, people develop apathy, a loss of initiative, and also losses in the sense of smell," said study author David Knopman, MD, of the Mayo Clinic in Rochester, MN, and member of the American Academy of Neurology.
"When you can't smell your food, it won't have much taste, and you might be less inclined to eat it. And, apathy and loss of initiative may make women less likely to prepare nutritious meals and more likely to skip meals altogether," Knopman added. Unlike women, men in this study who later developed dementia did not lose weight in the years before diagnosis.
According to Knopman, the difference could be due to hormones, but a social reason seems just as likely. "Middle-aged and elderly men are less likely to be preparing their own meals. Their spouses or adult children were more likely making meals for them, which would lessen the effect of the apathy, loss of initiative and loss of sense of smell," he said.
The study conflicts with others suggesting that obesity in middle-age may be a risk factor for dementia. Obesity is also associated with diabetes, hypertension, and cardiovascular disease, which are risk factors for dementia.
"We'll need to do more research to look into these differences," Knopman said. The study is published in the August 21, 2007, issue of Neurology.