Overview
- Researchers tracked 296 cognitively healthy adults aged 50–90 for up to 14 years in the Harvard Aging Brain Study, using a one‑week baseline step count, annual cognitive testing, and repeated PET scans.
- Measured benefits began around 3,000 steps a day and appeared largest between roughly 5,000 and 7,500 steps, with little additional effect at higher counts.
- The slower tau accumulation and cognitive decline were most evident in participants who already had elevated beta‑amyloid at baseline, and step counts showed no association with amyloid build‑up itself.
- Modeling in amyloid‑positive participants suggested substantial delays to marked cognitive decline: about 6.5 years if inactive, roughly 9.6 years with low activity, and approximately 12–14 years with moderate activity.
- Authors and independent experts stressed that the results are observational with steps measured only at baseline, potential confounding remains, and randomized or mechanistic trials are needed to test causality and refine activity guidance.