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Folks with elevated levels of a brain protein called beta amyloid tend to be more likely to develop Alzheimer's disease and experience rapid brain decline later in life, previous research has found.
"People who had elevated levels of amyloid, which is one of the earliest changes you see with Alzheimer's disease, had slower rates of cognitive decline and brain volume loss over time if they had greater levels of physical activity," said lead researcher Jennifer Rabin. She is a scientist with the Hurvitz Brain Sciences Program at the Sunnybrook Research Institute in Toronto.
It didn't take much exercise to enjoy this protection, either.
The data suggests that people who walked 8,300 to 8,900 steps per day significantly delayed the onset of Alzheimer's, Rabin said.
Previous studies have shown that older people who exercise generally tend to stay sharp longer into old age, but this new research shows physical activity is specifically protective for folks who have these early brain changes related to Alzheimer's, said Dr. Howard Fillit. He's executive director and chief science officer at the Alzheimer's Drug Discovery Foundation.
"This population is different than what's been studied before because you're looking at people who are clinically normal but have evidence of Alzheimer's disease in their brains," said Fillit, who wasn't involved with the research.
For this study, Rabin and her colleagues asked 182 participants in the Harvard Aging Brain Study to wear a pedometer for a week, to gauge their usual level of physical activity. Brain scans were used to detect levels of amyloid beta in their brains.
Beta amyloid tends to clump in the brains of Alzheimer's patients, collecting in sticky plaques between neurons and possibly disrupting brain cell function.
The researchers then tracked the participants over as many as seven years, with annual tests to check the status of their brain function. Repeat scans also were performed to see whether their brains had started to shrink, which is a sign of Alzheimer's progression.
The study found that people who walked more tended to stay sharper and experience a slower loss of brain volume.
Physical activity might be preserving brain function by reducing inflammation, improving overall flow of blood to the brain, or helping people get better sleep, Rabin said.
Exercise also has been associated with higher levels of BDNF [brain-derived neurotrophic factor], a brain chemical that "is the most powerful neuroprotective growth factor that we know," Fillit said.
"It doesn't have to be Tour de France-level training," Fillit said. "It can just be getting on a treadmill or an elliptical and getting your heart rate up."
Rabin warned that while physical activity apparently helps mitigate amyloid-related declines in brain function, people with higher levels of beta amyloid are not likely to age as well as those without any amyloid in their brains.
But it's possible that if those folks combine exercise with heart-healthy habits such as eating right and controlling their blood pressure, they might further reduce their risk of future brain loss, Rabin added.
"If you're engaging in a host of good lifestyle choices, you maybe could get yourself back to a normal aging trajectory," Rabin said.
The findings were published online July 16 in the journal JAMA Neurology and presented on the same day at the Alzheimer's Association International Conference, in Los Angeles.
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