Weight loss may be a preclinical indicator of Alzheimer's disease

The slow, steady weight loss associated with aging may speed up prior to the onset of Alzheimer's disease and related dementias, according to an article in the September issue of Archives of Neurology.

Changes that occur with aging, such as reduced appetite and diminishing height, may induce weight loss in older adults, according to background information in the article. Alzheimer's disease has also been linked to age-related weight loss. Those in the late stages of the disease can lose up to 2 pounds per year; those who lose more weight are more likely to progress quickly and to be placed in a nursing home.

David K. Johnson, Ph.D., and colleagues at Washington University School of Medicine, St. Louis, studied weight loss before the development of dementia in 449 healthy adults (192 men, 257 women). At the beginning of the study and then yearly for an average of six years, the participants were assessed for dementia, weighed and asked questions about their medical history.

Over the course of the study, 125 participants developed dementia related to Alzheimer's disease. Those who did weighed about eight pounds less at the beginning of the study than those who did not develop Alzheimer's disease. In addition, "an acceleration in the rate of weight loss was a harbinger of the change from non-demented status to dementia of the Alzheimer's type," the authors write. "Participants lost about .6 pounds per year while without dementia, but one year before the first symptomatic detection of dementia of the Alzheimer's type, the rate of weight loss in individuals doubled to 1.2 pounds per year." This association held when the researchers controlled for other factors that might influence weight loss, including age, sex, health status, hypertension (high blood pressure) and stroke history.

It is unclear exactly why weight loss is associated with dementia, the authors write. Some have hypothesized that individuals with dementia forget to eat, but this is unlikely given the finding that weight loss precedes the onset of memory problems and other dementia symptoms. Depression has also been suggested as a link, but although study participants with dementia were more depressed, depressed patients did not have any changes in body weight compared with those who were non-depressed. "There are reports of mild to moderate changes in taste and smell in healthy aging populations and in populations with dementia, and these factors need to be measured rigorously in future studies," the authors write. "Subtle gustatory changes could result in cumulative decreases in caloric intake or decreases in the quality of food consumed by individuals with dementia of the Alzheimer's type."

If these results are confirmed in larger studies, they conclude, "weight loss may be a preclinical indicator of Alzheimer's disease."