An accumulation of fat lurking around the organs of obese people is strongly linked to a buildup of Alzheimer's-linked proteins in the brain, new research finds.
Buildup of this visceral fat in middle age may boost levels of the two damaging brain proteins, called amyloid and tau, explained a team led by Dr. Mahsa Dolatshahi, of Washington University School of Medicine in St. Louis.
Actual symptoms of Alzheimer's disease may not arise until many years later.
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“Our study showed that higher visceral fat was associated with higher PET [scan] levels of the two hallmark pathologic proteins of Alzheimer’s disease — amyloid and tau,” Dolatshahi said. “To our knowledge, our study is the only one to demonstrate these findings at midlife where our participants are decades out from developing the earliest symptoms of the dementia that results from Alzheimer’s disease.”
Dolatshahi is a post-doctoral research associate at the university's Mallinckrodt Institute of Radiology. Her team's findings were presented Monday in Chicago at the annual meeting of the Radiological Society of North America (RSNA).
According to the Alzheimer’s Association, 6.9 million Americans aged 65 and older are now affected by Alzheimer’s disease — a number that could rise to 13 million by mid-century.
Dolatshahi's group wondered if there might be factors in mid-life that affect a person's late-life odds for Alzheimer's.
Their study of 80 middle-aged people (averaging 49 years) was focused on the potential effects of obesity and different types of body fat.
All of the individuals had no apparent cognitive issues at the time of the study. Just over half were obese (57.5%), with an average BMI of 32.3 (a BMI of 30 is the threshold for obesity).
For each participant, a series of PET scans were run to measure brain levels of amyloid and tau proteins, and abdominal MRIs were conducted to assess volumes of subcutaneous fat (fat lying under skin) and visceral fat (deep hidden fat surrounding the organs).
Tests were also run to gauge folks' levels of cholesterol, blood sugar and insulin.
The key finding was that levels of Alzheimer's-associated amyloid and tau in people's brains was closely linked to how much fat was collecting around their organs.
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This visceral fat accounted for 77% of the obesity-linked rise in levels of amyloid, the St. Louis team found. Levels of other types of fat didn't have any impact on amyloid.
Dolatshahi noted that there's long been a link between obesity and Alzheimer's risk, but the new study delves deeper.
“This study goes beyond using BMI to characterize body fat more accurately with MRI and, in so doing, reveals key insights about why obesity can increase risk for Alzheimer’s disease,” she said in an RSNA news release.
There's some good news from all of this, since there's a lot middle-aged people can do to reduce their levels of obesity and visceral fat.
“A key implication of our work is that managing Alzheimer’s risk in obesity will need to involve targeting the related metabolic and lipid issues that often arise with higher body fat,” said senior study author Dr. Cyrus Raji, an associate professor of radiology at Washington University.
A second study presented by the St. Louis group at the same meeting provided more insight.
That study involved both obese and non-obese people. It found that blood flow to an individual's brain appears to worsen as levels of visceral fat rise. No such relationship was seen for other kinds of fat, the team reported.
“This work will have a considerable impact on public health because nearly three out of four Americans are overweight or obese,” Raji said. “Knowing that visceral obesity negatively affects the brain opens up the possibility that treatment with lifestyle modifications or appropriate weight-loss drugs could improve cerebral blood flow and potentially lower the burden of and reduce the risk for Alzheimer’s disease.”
Still, these findings were presented at a medical meeting, so they should be considered preliminary until published in a peer-reviewed journal.