A study found that the habit of walking more than 3,000 steps a day may slow the progression of Alzheimer's disease. Alzheimer's is a degenerative brain disorder that accounts for two-thirds of dementia cases.
Researchers at Harvard Medical School said in Nature Medicine on the 4th that physical activity such as walking can slow cognitive decline in older adults at high risk of Alzheimer's.
The researchers tracked 296 adults ages 50 to 90 who participated in the Harvard Aging Brain Study for an average of nine years. Their average age was 72.3. All had no cognitive problems at the start of the study, but their brains had already accumulated amyloid beta, a protein cited as a cause of Alzheimer's. Amyloid beta normally protects nerve cells, but when it breaks off from cells and forms clumps, it is known to cause damage.
Participants measured their daily steps with pedometers worn on their waist and regularly underwent brain imaging and cognitive tests. The analysis found that those who walked 3,000 to 5,000 steps a day showed the onset of cognitive decline an average of three years later than those who did not. Those who walked 5,000 to 7,500 steps delayed it by as many as seven years.
According to the researchers' analysis, the greatest effect of exercise came from slowing the accumulation of tau protein. Tau, along with amyloid beta, is cited as a cause of Alzheimer's. It normally serves as a protein that acts as a connector maintaining the structure of nerve cells, but when it changes inside nerve cells, it tangles and causes problems with cognitive function.
People who barely moved, by contrast, experienced rapid buildup of tau protein in the brain and faster declines in memory and daily functioning. For those who did not walk, tau piled on top of the amyloid beta already in the brain, meaning dementia progressed faster. People whose initial amyloid beta levels were low showed little cognitive decline or tau accumulation over time, and the correlation with activity level was not large.
Professor Jasmeer Chhatwal, who led the study, said, this offers a clue to why some people on the Alzheimer's trajectory worsen more slowly, and noted that lifestyle factors were confirmed to affect the very earliest stage of the disease. In other words, changing lifestyle in the early phase of Alzheimer's can delay the onset of symptoms itself.
Co-researcher Professor Reisa Sperling said, this study shows that physical activity is a key factor in protecting brain health, and added that the findings will greatly help efforts to ultimately prevent dementia due to Alzheimer's and reduce dementia arising from multiple factors.
Julia Dudley of Alzheimer's Research UK said of the study that it does not prove a causal relationship that walking directly slows the progression of Alzheimer's, and added that more clinical trials are needed to determine the direct impact of exercise on preventing dementia or slowing its progression.
The Harvard Medical School team said it plans to further analyze how the intensity and pattern of exercise affect outcomes and to determine what biological actions exercise has on changes in brain proteins.
References
Nature Medicine (2025), DOI: https://doi.org/10.1038/s41591-025-03955-6