Experts often encourage people to take 10,000 steps a day as part of a healthy routine, but a new study has found that 3,000 steps or more appear to be able to delay the brain changes and cognitive decline experienced by Alzheimer's patients.
The results of the 14-year study showed that cognitive decline was delayed by an average of three years in people who walked 3,000 to 5,000 steps a day, and seven years in those who achieved 5,000 to 7,000 steps a day.
"We encourage older adults at risk for Alzheimer's to consider making small changes to their activity levels to build sustainable habits that protect or benefit their brain and cognitive health," said Dr. Wei-Ying Yao, lead author of the study at Brigham and Women's Medical Center in Boston.
Dementia affects an estimated 50 million people worldwide, with Alzheimer's disease being the most common cause. The condition is linked to the accumulation of two toxic forms of protein in the brain: amyloid-beta plaques and tau tangles.
Yao and her colleagues analyzed data from 296 people aged 50 to 90 who had no cognitive impairments at the start of the study. The data included annual cognitive assessments, step counts measured by a pedometer, and positron emission tomography scans to detect amyloid and tau levels in the volunteers' brains.
Individuals with initially low levels of brain amyloid showed very little cognitive decline or tau protein accumulation during the study period. The risk of developing Alzheimer's disease was higher for those with higher baseline amyloid levels, and a higher number of steps taken was associated with slower rates of cognitive decline and later tau protein accumulation. Among sedentary individuals, tau accumulation and cognitive decline were significantly faster.
Although scientists cannot rule out a reverse causal relationship—that early brain changes in Alzheimer's lead to reduced walking in old age—the data suggest that physical activity is protective. "We need randomized controlled trials to prove causality," Yao said, "b jiut it's very encouraging that physical activity may help modulate the course of disease progression in a person. If they have amyloid, the rate of decline may be slower if they are more physically active."
How exercise might help remains unclear, but physical activity improves blood flow, reduces inflammation, and raises levels of certain hormones and growth factors, all of which may play a role. "As for the potential mechanisms, that's the million-dollar question we want to look at in future studies," Yao said.
More research, including clinical trials, is needed to determine the direct effect of physical activity on preventing and slowing the progression of dementia, and on the underlying pathological causes.
