Older people in the study who were followed for an average of six years lost twice as much weight in the year before the first signs of appeared as people who did not develop Alzheimer's-related dementias -- 1.2 pounds compared with a weight loss of 0.6 pounds per year.
The acceleration in weight loss was too small to help physicians identify Alzheimer's earlier in individual patients, the study's researchers tell WebMD. But the finding may help researchers better understand the disease.
The new research appears in the September issue of the Archives of Neurology.
"We are getting glimpses into what is happening with the brain in the pre-symptomatic stage before dementia occurs," says David K. Johnson, PhD.
'Kicked Into High Gear'
Among patients already diagnosed with Alzheimer's-related dementia, rapid weight loss has long been associated with faster disease progression. But the course of weight loss prior to the development of memory loss and other symptoms of dementia has not been well understood.
The researchers used data from the Memory and Aging Project at the Alzheimer's Disease Research Center of Washington University in St. Louis, which is a long-term study assessing the impact of aging on the brain.
The study included 449 healthy adults between the ages of 65 and 95 with no clinical evidence of Alzheimer's-associated dementia at enrollment. The study participants were followed for an average of six years, during which time they were weighed and assessed for dementia annually.
During the study, 125 people developed dementia related to Alzheimer's disease. Those who did weighed an average of 8 pounds less than those who didn't at the beginning of the study.
The two groups tended to lose weight at the same rate of about 0.6 pounds a year for several years. But a year before early signs of dementia were first seen, the future Alzheimer's patients lost twice as much weight as the patients who didn't develop Alzheimer's.
"No matter what we did to control for other health variables, such as, , and , 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."
More Study Needed
The study is not the first to suggest a link between weight loss and the development of Alzheimer's disease.
Early in 2005, a long-term study involving 1,800 Japanese-American men followed for 32 years found that elderly men with dementia lost an average of 10% of their body weight in the years before they were diagnosed.
It remains unclear how and why Alzheimer's disease influences weight loss long before clinically recognizable symptoms appear.
There were no major differences in reported appetite among future Alzheimer's patients and those who did not develop dementia in the newly reported study.
Study researcher Consuelo Wilkins, MD, tells WebMD that a better understanding of weight loss prior to the development of Alzheimer's-related dementia may help researchers in their efforts to identify the disease earlier.
"Early detection is important because the medications that we have to treat Alzheimer's can only delay progression," she says. "The earlier treatment is started, the better."
This study was supported by grants from the National Institute on Aging.