CHICAGO - Unexplained weight loss in older people might be an early signal of Alzheimer's disease, appearing several years before the memory lapses that define the illness, according to an intriguing but unproven new theory.
Researchers at Chicago's Rush University Medical Center base the theory on their study of 820 Roman Catholic priests, nuns and brothers aged 75 on average who were followed for up to 10 years.
Otherwise healthy participants whose body-mass index fell the most were the most likely to develop Alzheimer's disease.
Study co-author Dr. David Bennett, director of the Rush Alzheimer's Disease Center, says the results raise the possibility that the disease attacks brain regions involved in regulating food intake and metabolism, as well as memory, and that weight loss is an early symptom.
Weight loss frequently occurs after an Alzheimer's diagnosis and has been attributed partly to memory lapses or lifestyle changes associated with becoming infirm. But it might be that brain changes that start well before diagnosis are another reason, Bennett said.
The results appear in the Sept. 27 edition of the journal Neurology.
Dr. Peter Rabins, an Alzheimer's researcher and professor of medicine at Johns Hopkins School of Medicine, said the research fits with an increasingly popular belief that Alzheimer's abnormalities "really are present for at least 10 years before there are any symptoms."
"The idea that something would start before it became clinically obvious no longer seems that far-fetched," Rabins said.
However, Rabins said he thinks it's likely that gradual weight loss stems from subtle behavior changes such as loss of initiative, which could result in less snacking or eating out, than in brain changes affecting metabolism.
Those behavior changes, involving parts of the brain associated with Alzheimer's, often precede the diagnosis, but "because it's a subtle thing, it's often not recognized except in retrospect," Rabins said.
Dallas Anderson of the dementias of aging branch at the National Institute on Aging, which funded the research, said the results are intriguing but that the theory needs further testing in a more diverse group.
When the study began, participants' average BMI was 27.4, in the overweight zone, and none had been diagnosed with Alzheimer's. By study's end, 151 had been diagnosed with the disease.
Those whose BMI dropped a point each year faced a 35 percent increased risk of being diagnosed with Alzheimer's later on, compared with those whose BMI remained stable.
Dr. Deborah Blacker, director of gerontology research at Massachusetts General Hospital in Boston, said depression sometimes precedes Alzheimer's and can also cause weight loss, which might at least partly explain the findings.
People tend to lose weight in old age because of loss of bone and muscle mass, but the researchers said factoring in age, chronic disease, gender and other characteristics that might have affected weight didn't change the results.