Physical activity baseline measurements predicted cognitive trajectories over an average 9.3-year follow-up. Amyloid-beta and tau protein both accumulate in Alzheimer's disease, with tau accumulation in the inferior temporal cortex associated with cognitive decline. Participants with elevated baseline amyloid showed marked differences based on daily activity levels.
Step counts and cognitive delay
Among those with high baseline amyloid, daily step counts of 3,000 to 5,000 correlated with an approximate 3-year delay in cognitive decline. Counts of 5,000 to 7,500 steps daily showed an approximate 7-year delay. Associations plateaued at the 5,000-7,500 step range. Participants taking 3,000 or fewer steps showed the fastest tau accumulation and steepest cognitive decline in this group.
Among participants with normal baseline amyloid levels, physical activity showed no meaningful correlation with cognitive outcomes, and cognitive decline was minimal overall.
How movement may slow decline
Mediation analysis revealed that slower tau accumulation explained 84 percent of the association between activity and slower cognitive decline on the PACC5 test in elevated-amyloid participants. For functional decline measured by the Clinical Dementia Rating scale, slower tau accumulation explained 40 percent of the relationship. Possible mechanisms include improved cardiovascular health, increased brain blood flow, and enhanced neurotransmitter production supporting synaptic connections.
Study design and limits
Amyloid scans included 241 participants, tau scans 172. The first tau imaging occurred an average 2.2 years after baseline because the technique was introduced during the study. Study author Wai-Ying Wendy Yau stressed that clinical trials are needed to establish causation, as the direction of causality remains unclear. Early Alzheimer's symptoms might reduce activity as much as activity might slow decline. Participants who walked more also showed better cardiovascular health, lower cholesterol, improved sleep, lower blood pressure, and reduced diabetes risk. These lifestyle factors often cluster together, making it difficult to isolate walking's independent effect.
Comparative evidence
A British cohort tracked over 8-10 years found moderate-to-vigorous activity reduced dementia risk by 34 to 50 percent. Among those who later developed dementia, sustained activity slowed memory decline, particularly in older women. A 2022 British study of 78,430 people wearing wrist accelerometers for seven years found daily step counts of 3,800 reduced dementia risk by 25 percent, rising to 50 percent at 9,800 daily steps. Researchers call for longer prospective studies examining activity intensity and duration alongside brain imaging biomarkers to clarify biological pathways.