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The body, and not the mind, might be the first thing to go in people with Alzheimer's and related dementias.
New studies show that brain tissue and body weight are lost before memories begin fading in elderly people who go on to have the diseases. The findings could lead to new types of early-warning tests for dementia before the diseases cause lasting damage.
In one study, detailed in the Sept. 12 issue of the journal Neurology, researchers compared the brain scans of 120 people belonging to three groups: 40 of the participants had mild cognitive impairment (MCI), a transition stage between normal aging and the more serious memory problems associated with Alzheimer's disease; 40 complained of significant memory problems but did not have MCI and 40 were healthy controls. All participants were 60 years or older.
Compared to healthy controls, those with MCI showed a 4-percent reduction of gray matter brain tissue in areas known to be important for memory, while those with memory problems but no MCI had a 3-percent reduction.
The findings suggest that the memory problems experienced by some people as they grow older are part of a "pre-MCI" stage of dementia, said study team member Andrew Saykin of Dartmouth Medical School in New Hampshire.
"This is important since early detection will be critical as new disease-modifying medications are developed in an effort to slow and ultimately prevent Alzheimer's disease," Saykin said.
Studies suggest that to prevent lasting cognitive damage, Alzheimer's treatments will have to be administered before memory loss occurs.
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In a separate study, researchers at the Washington University School of Medicine, Missouri, found that the steady weight loss normally associated with aging doubles in the year before symptoms of Alzheimer's-type dementia first become evident.
The study followed 449 elderly participants, many in their 70s and 80s but some as young as 65, for an average of six years. All of the participants had good cognitive health at the beginning of the study, but 125 were eventually diagnosed with mild dementia. Among this latter group, the rate of weight loss doubled, from 0.6 pounds per year to 1.2 pounds per year shortly before their diagnosis.
"The two groups lost weight at about 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," said study team-member David Johnson.
Interestingly, the group of volunteers who did experience dementia weighed about eight pounds less on average at the beginning of the study than those who did not develop dementia. The reason for the difference is unclear, but one hypothesis is that a process related to Alzheimer's becomes active earlier in the lives of the affected individuals, driving their weight down. Another is that people with lower average weight are more vulnerable to Alzheimer's.
Weight loss is a normal part of aging. Studies suggest people begin losing about half a pound per year in their late 50s and early 60s. Scientists suspect the decline is associated with the physical shrinking of the body that occurs in old age, loss of interest in eating or the wasting effects of cancers and other health problems.
Body weight can vary greatly within a given year, so weight loss alone can't serve as a definite indicator of dementia, Johnson said, but it could become part of a battery of tests for detecting early warning signs for Alzheimer's before the disease progresses.