Key takeaways
- The Lancet Commission 2024 identified 14 modifiable risk factors linked to approximately 45% of dementia cases worldwide — physical inactivity and poor sleep are both on that list.
- Aerobic exercise is consistently associated with larger hippocampal volume and slower age-related cognitive decline across multiple large cohort studies and meta-analyses.
- BDNF (brain-derived neurotrophic factor) — the brain's own growth protein — rises acutely after moderate-to-vigorous cardio, supporting neuroplasticity and memory formation.
- Resistance training contributes independently to executive function and processing speed, making a combined cardio-plus-strength routine optimal for brain health.
- Brain-training apps show limited 'far transfer' to real-world cognition — movement, sleep, and social engagement remain the most proven non-pharmacological protective factors.
The Short Answer
Regular physical exercise is the single most evidence-backed lifestyle lever for protecting the ageing brain. It raises BDNF, supports hippocampal volume, improves cerebrovascular health, and is explicitly named in the Lancet Commission's 2024 dementia prevention framework as a modifiable risk factor. The evidence is not preliminary — it spans decades of cohort data, multiple meta-analyses, and mechanistic research. Whether you are 40 or 70, the brain responds to movement.
General information, not medical advice. Consult your GP if you have concerns about memory or cognition.
How the Brain Changes With Age
The brain begins to change structurally and functionally from the fourth decade of life. Grey matter volume declines gradually, white matter integrity reduces, and processing speed slows. The hippocampus — the region most critical for forming new memories — is particularly vulnerable, shrinking at roughly 0.5–1% per year in sedentary older adults.
Cerebral blood flow also reduces with age, affecting the delivery of oxygen and glucose to neurons. Neuroinflammation increases, synaptic plasticity diminishes, and the brain's capacity to clear metabolic waste — including amyloid and tau proteins implicated in Alzheimer's disease — declines during poor sleep.
None of this is inevitable at the rate it happens in sedentary people. The trajectory is partly modifiable. And the most powerful modifier is also the most accessible: structured physical activity.
Exercise, BDNF, and Hippocampal Volume
BDNF — brain-derived neurotrophic factor — is often described as the brain's own fertiliser. It supports the survival of existing neurons, encourages the growth of new ones (neurogenesis), and strengthens synaptic connections that underpin learning and memory. BDNF levels tend to decline with age and are lower in people with depression and cognitive impairment.
Aerobic exercise is one of the most reliable ways to acutely elevate BDNF. Even a single session of moderate-to-vigorous cardio raises circulating BDNF, and regular training sustains elevated baseline levels. This is likely one of the key mechanisms behind exercise's cognitive benefits.
The structural evidence is striking. Multiple studies using MRI have shown that older adults who exercise regularly have greater hippocampal volume than sedentary peers of the same age. A landmark randomised controlled trial found that one year of aerobic exercise increased hippocampal volume by approximately 2% in older adults — effectively reversing one to two years of age-related shrinkage.
Perhaps more practically relevant: aerobic exercise training is consistently associated with slower cognitive decline across long-term cohort studies, even after adjusting for cardiovascular health, education, and baseline cognitive status.
Cardio vs Strength for Cognition
The debate between cardio and resistance training is largely a false one — the evidence supports both, acting through complementary mechanisms.
Aerobic exercise (brisk walking, cycling, swimming, rowing, jogging) has the most extensive evidence for hippocampal volume, episodic memory, and overall cognitive function. It improves cerebrovascular health — capillary density in the brain, endothelial function, and the efficiency of oxygen delivery — which matters enormously for neural resilience.
Resistance training shows consistent associations with executive function (planning, attention, inhibitory control) and processing speed. A 2018 systematic review and meta-analysis (Northey et al., BJSM) found that resistance training significantly improved cognitive function in adults aged 50 and above, with particular benefits for executive function and memory. The mechanisms likely involve IGF-1 signalling, reduced neuroinflammation, and metabolic improvements.
For optimal brain health, the recommendation is the same as for physical health: combine both modalities. If you are currently sedentary, any increase in structured movement will yield cognitive gains. See how to improve your VO2max and strength training and ageing for practical starting points.
The Lancet Commission: 14 Modifiable Risk Factors
The Lancet Commission on dementia prevention, intervention, and care published its most comprehensive update in 2024. The finding that makes exercise so important: approximately 45% of dementia cases globally are linked to 14 modifiable risk factors. Physical inactivity is one of them — alongside poor sleep, excessive alcohol, hearing loss, hypertension, obesity, depression, diabetes, smoking, air pollution, social isolation, traumatic brain injury, low levels of education, and elevated LDL cholesterol.
This matters for two reasons. First, it confirms that dementia is not simply genetic fate — lifestyle matters. Second, regular exercise addresses not just physical inactivity but simultaneously improves blood pressure, blood glucose, body weight, mood, and sleep quality. It is the single intervention with the widest overlap across the risk factor list.
The Alzheimer's Society notes that while no proven prevention exists, evidence increasingly supports that what is good for cardiovascular health is also good for brain health. This aligns with the Republic Method's core premise: build the body, protect the mind.
Sleep, Social Connection, and Cognitive Load
Exercise does not operate in isolation. Three other pillars are consistently supported by the evidence:
Sleep is when the brain consolidates memory (moving it from short- to long-term storage) and clears metabolic waste via the glymphatic system. Chronic poor sleep — defined as less than six hours habitually — is now explicitly named in the Lancet Commission framework as a modifiable dementia risk factor. Adults need seven to nine hours; older adults seven to eight hours. Read sleep and ageing for the evidence and practical guidance.
Social engagement — having meaningful human connection, a sense of purpose, and mental stimulation — is associated with lower dementia risk in large cohort studies. Isolation is a named risk factor. Exercise often provides a route to social connection: group classes, team sports, working with a coach.
Cognitive challenge — learning new skills, languages, instruments, or engaging in complex problem-solving — is associated with building 'cognitive reserve', the brain's resilience against pathology. Formal education is a risk factor in the Lancet Commission model, but lifelong intellectual engagement continues to contribute across the lifespan.
What Is Proven vs What Is Marketed
Brain-training apps
Commercially available brain-training platforms improve performance on the specific tasks they use. The evidence for far transfer — improvements in general cognition, real-world memory, or dementia risk — is weak. A large independent review commissioned by the Stanford Center on Longevity, signed by over 70 leading cognitive scientists, concluded that the claims made by many commercial brain-training companies outrun the evidence. Physical exercise, by contrast, has robust and replicated effects on the very neural structures these products claim to target.
Nootropics and cognitive supplements
No nootropic supplement is proven to prevent or slow dementia in healthy adults. Some — like omega-3 fish oil — have plausible mechanisms and mixed evidence for supporting cognitive health, particularly when addressing dietary deficiency. Creatine has emerging data for cognitive function, especially under conditions of sleep deprivation or mental fatigue. Vitamin D deficiency is associated with cognitive decline — correcting deficiency is sensible, megadosing is not. See longevity supplements: an honest overview for the full evidence ladder.
The honest framing: supplements may support a healthy lifestyle but cannot replace movement, sleep, and social connection. The brain responds to exercise in ways no pill has matched in human trials.
Practical Recommendations
To protect brain health across the lifespan, the evidence converges on the following:
- 150–300 minutes per week of moderate aerobic exercise (brisk walking, cycling, swimming) or 75–150 minutes vigorous — meeting the WHO/NHS guidelines
- Resistance training on at least two days per week — targeting all major muscle groups
- Consistent sleep of seven to nine hours — not just quantity but regularity and quality
- Social engagement and cognitive challenge built into daily life
- Management of cardiovascular risk factors — blood pressure, blood glucose, body weight — ideally with your GP
If you are currently inactive, even beginning with 20–30 minutes of brisk walking most days produces measurable benefits. You do not need to be an athlete. You need to be consistent.
A personalised programme from a coach who understands both the exercise science and your specific starting point will always outperform a generic plan. Book a free consultation to build a routine that protects your body and your brain — or take the free Blueprint quiz to get a personalised starting point in minutes.
When to See Your GP
Normal age-related changes include occasionally forgetting names or words, slowing down on complex tasks, and taking longer to learn new information. These are annoying but not necessarily concerning.
See your GP if you or someone close to you notices: memory lapses disrupting daily life, getting lost in familiar places, repeating questions in the same conversation, personality or mood changes, difficulty with financial decisions, or a sudden step-change in any cognitive ability. The NHS offers memory clinics and cognitive assessments. Early assessment is always better than delay.
This guide is general information, not medical advice. If you have concerns about your memory or cognition, speak to your GP.
The Verdict
The most powerful tool for protecting the ageing brain does not come in a capsule or an app. It is the sustained, progressive physical activity programme that raises your VO2max, builds your strength, keeps your cardiovascular system healthy, and produces BDNF with every session. Combined with restorative sleep and an engaged social life, it represents the clearest evidence-based strategy for maintaining cognitive function through the decades ahead.
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Book a free consultationSources & further reading
- Livingston et al., Lancet Commission on Dementia Prevention, Intervention, and Care 2024 — The Lancet
- Alzheimer's Society — Managing the risk of dementia — Alzheimer's Society
- NHS — Dementia — Prevention — NHS
- WHO Guidelines on Physical Activity and Sedentary Behaviour 2020 — WHO
- Erickson et al. — Aerobic exercise increases hippocampal volume in older adults, PNAS 2011 — PNAS
- Northey et al. — Exercise interventions for cognitive function in adults older than 50, BJSM 2018 — BJSM
Citations are provided for transparency. This is general information, not medical advice — always consult a qualified professional about your own circumstances.