Link between weight loss and dementia

A long-term study of the elderly has revealed that their average rate of weight loss doubles in the year before symptoms of Alzheimer's-type dementia first become detectable.

The finding may be useful to researchers seeking ways to detect and treat Alzheimer's before it causes irreversible brain damage.

The study is the first to confirm in precise detail a link between weight loss and dementia tentatively identified a decade ago. Researchers report in the September 2006 Archives of Neurology that one year before study volunteers were diagnosed with very mild dementia, their rate of weight loss doubled from 0.6 pounds per year to 1.2 pounds per year. The analysis used data from the Memory and Aging Project at the Alzheimer's Disease Research Center (ADRC) of Washington University School of Medicine in St. Louis.

Alzheimer's researchers are working hard to find biomarkers, indicators that can be used to detect the presence of Alzheimer's before clinical symptoms become obvious. Studies at the ADRC and elsewhere have strongly suggested that if Alzheimer's treatments will ever prevent lasting cognitive damage, they may have to be given to patients before memory loss and other disruptions caused by the disorder are evident.

"A person's weight can vary substantially in a given year, so weight loss alone can't serve as a definite indicator for physicians," says David K. Johnson, Ph.D., research instructor in neurology. "But it's interesting from a biochemical perspective--we don't know why these two phenomena are linked. And weight loss may one day be incorporated into a battery of biomarkers that physicians keep their eyes on for early warning of Alzheimer's-type dementia."

The Memory and Aging Project, which began in 1979, is a long-term study of the links between cognitive health and aging. The project is made possible through the cooperation of hundreds of volunteers age 65 and older who undergo a detailed annual evaluation of their cognitive, neurological and physical health.

In 1991, investigators added patient weight to this annual assessment. According to Johnson, the scientific information available on weight loss in the elderly is sparse. Studies have suggested that weight generally begins a slow but steady decline of about half a pound per year in the late 50s and early 60s. Gerontologists have speculated that the decline may be attributable to physical shrinkage of the body seen in old age, loss of interest in eating or the wasting effects of cancers and other health factors.

The study analyzed data on 449 participants, most in their 70s and 80s but some as young as 65. All were cognitively normal at the beginning of the study but 125 were eventually diagnosed with mild dementia.

"Interestingly, the group of volunteers who did become demented started the study weighing about eight pounds less on average than the patients who did not develop dementia," Johnson notes. "The two groups lost weight at the same rate for four to five years, and then one year before the detection of even the mildest cognitive symptoms, weight loss increased in the group that would eventually be diagnosed with mild dementia."

It's unclear why the group that developed dementia began the study at a lower average weight. Johnson speculates that a process somehow related to Alzheimer's might have become active earlier in the participants' lives and started to drive their weight down. Alternatively, persons with lower average weight may be more vulnerable to Alzheimer's.

"No matter what we did to control for other health variables, such as diabetes, stroke and hypertension, none of them could account for this effect," Johnson says. "Sometime between the last evaluation when they were healthy and this first evaluation when they had mild dementia, a metabolic process kicked in, or kicked into higher gear, and made their Alzheimer's detectable. And increased weight loss went hand-in-hand with that change."