Overview
- A Nature Medicine analysis of 296 cognitively unimpaired participants in the Harvard Aging Brain Study found that higher step counts correlated with slower decline only in those with elevated amyloid at baseline.
- Walking 3,000–5,000 steps per day was associated with about a three-year delay in decline, and 5,000–7,500 steps with roughly a seven-year delay, with benefits plateauing above about 7,500 steps.
- Physical activity was linked to slower accumulation of tau—particularly in the inferior temporal cortex—not to changes in amyloid, and statistical modeling suggested tau largely mediated the cognitive benefit.
- The study was observational with step counts recorded over a single week at baseline, leaving room for confounding and reverse causation, and experts cautioned that randomized trials are needed to test causality.
- The authors plan further work on activity intensity and longitudinal patterns and say the findings can guide trials and public messages that emphasize achievable activity targets for at-risk older adults.