Walking a few thousand steps a day can slow cognitive decline in older adults who are at increased risk of developing Alzheimer’s disease, according to research published this month. Getting about 3,000 to 5,000 daily steps was advantageous compared with doing less physical activity; the benefit peaked around 5,000 to 7,500 steps.
The link between exercise and dementia is well established, and many neurologists say physical activity is one of the best ways to reduce the odds of developing the condition. The new study, published in the journal Nature Medicine, sheds light on what might be playing out in the brain and who could benefit most from exercise.
“We’ve known for several decades that physical activity is associated with a reduced risk of developing dementia,” said Kirk Erickson, chair of neuroscience at the AdventHealth Research Institute, who was not involved with the research. What the new study has done that is “really quite important and unique,” he said, is identify how exercise might be influencing some of the proteins implicated in Alzheimer’s disease.
The study followed nearly 300 older adults between the ages of 50 and 90 for an average of nine years. None of the participants had cognitive impairment at the start of the study, but about 30% had a considerable buildup of the protein amyloid-beta in their brains.
Amyloid buildup, often referred to as plaques, is a hallmark of Alzheimer’s. But prior research has shown that roughly 10% of 50-year-olds and 44% of 90-year-olds have amyloid plaques without signs of cognitive impairment.
“What differentiates those people from people that do develop cognitive decline over time?” said Dr. Jasmeer Chhatwal, a neurologist at Massachusetts General Hospital, who led the research, which sought to find “baseline characteristics that predict that.”
When the participants enrolled in the study, they received a pedometer that they wore for a week to establish their average daily step count. They underwent cognitive testing annually and PET scans every few years to look for amyloid plaques and the accumulation of another protein related to Alzheimer’s, called tau.
Researchers think that in Alzheimer’s disease, amyloid builds up first, and that triggers “tangles” of tau to form inside neurons and spread through the brain. It is primarily those tangles, not the amyloid plaques, that cause brain cells to malfunction, resulting in cognitive impairment.
The number of steps someone took each day didn’t appear to affect their amyloid levels, but it did correlate with the amount of tau tangles they developed and if they experienced cognitive decline. Among the participants with more amyloid in their brains, those who got little to no physical activity developed more tangles and had worse cognition after nine years. Walking 3,001 to 5,000 steps a day corresponded to less tau accumulation and slower cognitive decline. People who took more than 5,000 steps a day fared even better, but getting more than 7,500 steps did not confer an additional benefit.
People with minimal amounts of amyloid in their brains did not see any changes in either tau or cognition related to their step count. Chhatwal said that may be because those individuals were unlikely to experience significant tau buildup or cognitive decline since they didn’t have high levels of amyloid to begin with.
Erickson cautioned that these results are observational, so another factor may explain the connection between physical activity, cognition, and tau.
What’s more, because the participants only wore a pedometer for one week at the beginning of the study, their daily step counts could have increased or decreased over the years.
Judy Pa, a professor of neurosciences at the University of California, San Diego, called the new research “fascinating.” But she pointed out that the study included a relatively small number of participants, most of whom were white and well educated. “Can we replicate it in a multiethnic cohort?” she said.
The number of steps needed to see a benefit is consistent with other research on physical activity in older adults, said Amanda Paluch, an associate professor of kinesiology at the University of Massachusetts Amherst, who was not involved in the new study. In research she conducted, older adults had a lower risk of dying from multiple causes if they got roughly 6,000 steps per day.
One way physical activity may protect against cognitive decline is by increasing blood flow to the brain. That keeps neurons oxygenated and nourished so they can function optimally. Improved vascular health can also help the brain rid itself of the toxic proteins that start to accumulate. Exercise reduces inflammation in the brain, too, and inflammation is closely linked to Alzheimer’s.
Virtually everyone who exercises will experience these brain benefits to some degree. But the new research suggests that people who are at the greatest risk of cognitive decline may stand to gain the most.
People with preexisting amyloid plaques can see an acceleration of disease progression if they’re sedentary, Chhatwal said. “But the good news is that even kind of moderate levels of activity” are protective.
This article originally appeared in The New York Times.
