Study author Dr. Jeffrey M. Burns of the University of Kansas School of Medicine in Kansas City said the findings challenge the research that showed people who are overweight in middle age are more likely to develop Alzheimer's disease decades later than people at normal weight.
Burns and colleagues examined 506 people with advanced brain imaging techniques. They also analyzed cerebrospinal fluid to look for biomarkers for Alzheimer's disease, which can be present years before the first symptoms begin.
The participants, part of the Alzheimer's Disease Neuroimaging Initiative, included people with no memory problems, people with mild cognitive impairment, or mild memory problems and people with Alzheimer's disease, Burns said.
The study, published in the journal Neurology, found 85 percent of the people with mild cognitive impairment who had a body mass index below 25 had signs of the beta-amyloid plaques in their brains, compared with 48 percent of those with mild cognitive impairment who were overweight. This relationship was also found in people with no memory or thinking problems.