"Weight loss may be a manifestation of the disease process progressing," said Eric Vidoni, lead author of a study appearing in an issue of Neurology. "This may be further evidence for body-wide or systemic changes associated with Alzheimer's disease and it certainly supports the idea that Alzheimer's disease-related changes could be silently occurring, i.e., a 'preclinical' phase."
The findings may hold implications for diagnosis, prevention or treatment, but these are likely to be years or even decades away.
"A long history of declining weight or BMI (body mass index, a ratio of weight to height) could aid the diagnostic process," said Vidoni, who is assistant director of the University of Kansas Alzheimer's Disease Center in Kansas CityIs.
"At this point, though, it's too early to make body composition part of the diagnostic toolbox," he added.
"If weight loss is part of the disease process, this could suggest, along with the many papers linking metabolic dysfunction with AD, that preventing such dysfunction could reduce the progression of AD," said Ian Murray, an assistant professor of neuroscience and experimental therapeutics at the Texas A&M Health Science Center College of Medicine. "Of course this is, at present, speculative."
Previous studies have found that people who are overweight in middle age or earlier have a higher risk of developing Alzheimer's. And those who are overweight in their later years actually may have a lower risk of Alzheimer's, something known as the "obesity paradox."
Vidoni and his partners looked at PET (positron emission tomography) imaging of the brain and analyzed cerebrospinal fluid for markers of Alzheimer's disease in 506 people. Participants represented a range of cognitive function, some with no memory problems, some with mild cognitive impairment and some with Alzheimer's.
People with evidence of Alzheimer's - either in brain scans or protein levels in the cerebrospinal fluid - were more likely to have a lower BMI than those who did not show early evidence of the disease.
Number of theories
And the markers of brain changes for Alzheimer's were most evident in people with normal memory functioning or mild cognitive impairment, although it's not clear yet why this is.
There are a number of theories - but only theories at this point - to explain the findings.
One is that the Alzheimer's disease process is affecting the hippocampus, that part of the brain involved in metabolism and appetite.
Or inflammatory processes may be driving both the decreased BMI and the cognitive changes.
The Alzheimer's Association has more on has more on this condition.
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