Does low physical activity reduce neurotrophic signaling and hippocampal support in older adults?

Low physical activity in later life is most convincingly linked to less favorable hippocampal structural maintenance; links to neurotrophic signaling and cognitive reserve are biologically and longitudinally plausible but less direct.

Clinical and structural evidence

• In sedentary older adults, a 12-month moderate-intensity walking program increased bilateral anterior hippocampal volume by about 2%, whereas stretching/toning controls declined by approximately 1.4%. Hippocampal-volume gains correlated with improved spatial memory.
• Longitudinal accelerometry data also associate greater sedentary time with faster hippocampal volume loss over roughly 4.7 years, although earlier evidence across 29 studies was heterogeneous.
• Higher daily or actigraphy-measured activity in older cohorts was associated with better cognition and attenuation of pathology-related cognitive decline, including amyloid-associated decline. These results are consistent with greater cognitive resilience, but do not prove that activity directly builds or preserves cognitive reserve.

Neurotrophic and mechanistic evidence

• A meta-analysis of 35 randomized trials in older adults found that ≥4 weeks of exercise increased resting circulating BDNF (standardized mean difference 0.56, 95% CI 0.28–0.85). BDNF–TrkB signaling is relevant to neuronal survival and synaptic plasticity.
• The walking trial’s hippocampal gains were also associated with higher serum BDNF, but circulating BDNF is an indirect marker: it does not demonstrate increased hippocampal BDNF, TrkB activation, neurogenesis, perfusion, or connectivity in humans.

Interpretation for a 77-year-old

• Exercise-responsive hippocampal outcomes are supported specifically in older adults. In contrast, objectively measured habitual activity has not consistently correlated with resting serum BDNF, and observational cognition findings can partly reflect early disease, frailty, vascular illness, or depression reducing activity.

Bottom line

• Low activity likely provides less support for hippocampal health and may reduce BDNF-related and cognitive-resilience support, but the strongest evidence favors benefits of increasing sustained physical activity rather than proof that low activity directly causes impaired neurotrophic signaling or reduced cognitive reserve.