A study published in November 2025 in Nature Medicine by researchers from Mass General Brigham suggests that daily walking may delay cognitive decline in adults at risk of Alzheimer's disease. The study followed 296 volunteers aged 50 to 90 years, who did not initially have memory problems, over a median duration of 9.3 years, sometimes up to 14 years. Researchers measured activity levels using pedometers worn at the waist for a week, providing more objective data compared to self-reported questionnaires. The results indicate that walking between 3,000 and 5,000 steps per day delayed the onset of cognitive decline by about three years, while walking between 5,000 and 7,500 steps per day delayed it by approximately seven years. The protective effect plateaued beyond 7,500 steps, suggesting that excessive walking is not necessary for continued brain protection. These findings highlight the potential of simple, everyday activities in influencing brain health. The study highlights the role of physical activity in slowing the accumulation of the tau protein in the brain, which forms tangles inside neurons and is closely associated with their degeneration. Unlike amyloid plaques, which are not affected by physical activity, the slowing of tau accumulation explains 84% of the link between walking and slower cognitive decline. However, the benefits were only observed in individuals whose brains already showed an excess of amyloid, indicating that exercise acts primarily as a brake once the Alzheimer's disease mechanism is triggered. The exact mechanism by which physical activity affects tau remains debated. Researchers suggest possibilities such as a decrease in inflammation or an increase in molecules like BDNF and VEGF-A, which are known to nourish and protect neurons. However, the study remains observational, and part of the effect could be the reverse, with an invisible disease already causing people to move less. The authors aim to verify in future trials whether increasing the number of steps actually slows tau accumulation, potentially transforming daily walking into a quantified medical recommendation.