Does regular aerobic physical activity improve insulin sensitivity and support hippocampal plasticity?

Regular aerobic activity has particularly strong relevance for an older sedentary adult because direct trial evidence includes adults aged 57–83 with glucose intolerance and abdominal obesity. The claim is well supported for insulin sensitivity and for the biological role of BDNF-related signaling in hippocampal plasticity; the cerebral-blood-flow portion is more conditional.

Metabolic and cerebrovascular evidence

• Insulin sensitivity: In a 6-month randomized trial of 136 sedentary, abdominally obese older adults, aerobic training improved insulin resistance versus no exercise. In another 6-month trial of 28 adults aged 57–83 with glucose intolerance, aerobic exercise increased clamp-measured glucose disposal versus stretching (P=0.05). Muscle contraction increases glucose uptake through insulin-independent pathways, while training raises skeletal-muscle GLUT4 abundance; acute benefits may persist roughly 24–72 hours, favoring regular activity.
• Cerebral circulation: A 12-week supervised program in adults aged 57–75 increased hippocampal and anterior-cingulate perfusion, with hippocampal-flow improvement associated with memory gains. In sedentary obese older adults, 16 weeks improved hypercapnic and cognitive-stimulus cerebrovascular reactivity. Yet other 6-month trials found no whole-brain-flow or reactivity change, and meta-analyses are mixed. Benefits appear regional and population-specific rather than a dependable global-flow increase.

Neurotrophic and hippocampal mechanisms

• In older adults with mild cognitive impairment, meta-analytic evidence found higher peripheral BDNF after regular exercise, including a significant aerobic subgroup and interventions ≥16 weeks, although another meta-analysis was nonsignificant.
• Preclinical evidence directly implicates hippocampal BDNF–TrkB signaling: running doubled surviving newborn dentate-gyrus cells in mice, and progenitor-cell TrkB loss prevented running-related proliferation and neurogenesis. A 1-year older-adult trial reported ~2% bilateral hippocampal-volume gain, but pooled RCT evidence was not significant.

Bottom line

• Regular aerobic activity reliably improves insulin sensitivity and has biologically compelling links to BDNF-dependent hippocampal plasticity. It may improve regional brain perfusion and vascular reactivity, especially in sedentary higher-risk older adults, but should not be presented as reliably increasing global cerebral blood flow.