Does regular physical activity support cerebral blood flow, insulin sensitivity, and neurotrophic signaling involved in synaptic plasticity?

Regular physical activity has well-supported metabolic and neurotrophic effects, and lower activity is consistently linked to poorer cognitive outcomes. For an 83-year-old man, the evidence favors an individualized, feasible activity program, while avoiding claims that exercise reliably increases global brain perfusion or definitively prevents dementia.

Clinical and cognitive evidence

• Exercise improves insulin sensitivity. Across 25 randomized trials (851 adults; ≥4 weeks), insulin-stimulated glucose disposal improved by a moderate amount (SMD 0.52, 95% CI 0.39–0.65). In 12 resistance-training trials in older adults, HOMA-IR decreased modestly (d −0.25, 95% CI −0.43 to −0.06).
• Inactivity and sedentary behavior are associated with higher later dementia/cognitive-impairment risk: regular activity was associated with lower dementia incidence (RR 0.75), while ≥8 hours/day sitting was associated with higher risk (RR 1.27). Device-based UK Biobank estimates found an adjusted dementia HR of 3.21 at 15 versus 9.27 sedentary hours/day. These are associations, potentially influenced by preclinical disease, frailty, and other confounding.
• In amnestic MCI, a 12-month aerobic-exercise trial improved memory versus stretching. Exercise may also reduce falls in community-dwelling people with dementia, though this evidence is based on few heterogeneous studies.

Mechanisms and cerebrovascular effects

• Exercise increased circulating BDNF in MCI/dementia trials (mean difference 81.58, 95% CI 54.86–108.30; 3 trials, 69 participants; MCI pooled SMD 0.32, 95% CI 0.09–0.56). BDNF–TrkB signaling engages ERK/MAPK, PI3K/Akt, and CaMKII pathways; experimental blockade reduces exercise-associated hippocampal long-term potentiation and memory benefit.
• Cerebral perfusion effects are plausible but inconsistent: MCI trials show selective regional perfusion changes, whereas reviews and an Alzheimer disease RCT did not show reliable global CBF or cerebrovascular-reactivity improvement.

Bottom line

• Physical activity is strongly supported for insulin sensitivity and neurotrophic signaling, and inactivity is credibly linked to cognitive risk. Its brain-perfusion and dementia-prevention effects remain less certain; select aerobic and resistance activity based on function, fall risk, comorbidities, and—if using insulin—hypoglycemia planning.