Does exercise protect the brain? The aging brain, memory, and physical activity

Short answer

Regular physical activity is associated with reduced cognitive decline and dementia risk, and there is a biologically plausible mechanism behind this association: exercise supports the brain region involved in memory (the hippocampus) and a nerve growth factor that nourishes it (BDNF). In a randomized trial, aerobic exercise reversed age-related loss of hippocampal volume in older adults and improved memory.

An honest framing: These data are strong and promising; but they are not yet sufficient to say "exercise prevents/treats dementia." Observational studies do not prove causation, and animal studies show mechanism. Still, the evidence is strong enough to make exercise a reasonable and low-risk investment in brain health.

What does the evidence say?

Population studies (at the association level):

In analyses pooling long-term follow-up studies, high physical activity levels are associated with a marked reduction in cognitive decline and dementia risk compared with low levels (roughly a one-quarter to one-third lower dementia risk across various studies).
The Lancet dementia commission states that a significant portion of the dementia burden is associated with modifiable risk factors, physical inactivity being one of them.

Experimental human evidence (hippocampus):

In a randomized trial in older adults (Erickson et al., 2011), one year of aerobic exercise increased the volume of the anterior hippocampus by about 2% — corresponding to reversing the 1–2 years of volume loss normally expected at this age — and improved spatial memory. The increase in volume was associated with higher BDNF levels.

Mechanism (BDNF): BDNF is a protein that supports the survival of nerve cells, the formation of new connections, and learning–memory processes. Exercise increases BDNF production; this is considered one of the likely mediators of exercise's cognitive effects.

A contribution to this field of research: our own studies

Our studies investigating the effects of exercise on the brain in animal models have also contributed to this mechanistic literature:

We showed that regular aerobic exercise reduced anxiety while increasing irisin levels in the brain and adipose tissue in mice (Neuroscience Letters, 2018).
We found that voluntary regular exercise in female mice was associated with an increase in oxytocin together with reduced anxiety and increased empathy-like behaviors (Balkan Medical Journal, 2019).

An important limitation: These two studies are mouse models; they offer a mechanism for how exercise might affect brain biology, but they do not constitute direct evidence for anxiety or dementia in humans. Preserving this distinction when carrying animal findings over to humans is a requirement of honest science communication.

How much exercise? (World Health Organization, 2020)

Adults (18–64):

150–300 minutes of moderate-intensity or 75–150 minutes of vigorous-intensity aerobic activity per week
Muscle-strengthening working the major muscle groups on at least 2 days per week

Aged 65 and over: In addition to the above, multicomponent activity including balance and strength on at least 3 days per week — to maintain function and prevent falls.

Is "interval" or "steady-state" better? Both are beneficial; high-intensity interval work may produce a greater acute increase in some markers (e.g., post-exercise BDNF), but the "best prescription" for long-term cognitive benefit has not yet been settled. The best program is the one you can sustain.

For clinicians

The strength of the evidence varies by its source; conveying this to the patient as it is is the most correct approach:

Observational studies (following active people for years) show a strong association between exercise and lower dementia risk — but on their own cannot say "exercise prevents dementia," because inactivity may also be an early sign of the disease, and factors such as education, income, and general health may confound the outcome.
Human trials show that exercise improves intermediate measures such as hippocampal volume and memory tests; however, studies proving that it "reduces dementia in the long term" are limited, and some large trials have failed to show a clear benefit on cognition.

For this reason, when talking with a patient it is more honest to say "is associated with / may support" rather than "prevents." Still, the risk of exercise is very low and it has additional benefits for cardiovascular, metabolic, musculoskeletal, and mental health; therefore recommending physical activity is strongly justified in any case.

Frequently asked questions

Does exercise prevent dementia?

The evidence is not yet sufficient to say "prevents" definitively. But regular physical activity is consistently associated with lower dementia and cognitive decline risk and has a plausible mechanism. The correct statement: exercise supports brain health and may help reduce risk; it is not a guaranteed treatment.

Which exercise is best for the brain?

No specific "best" type has been proven. Both steady-state aerobic activity and high-intensity interval work are beneficial; strength and balance work are especially important in older age. The World Health Organization's weekly targets are a good framework. The most effective program is the one you can sustain regularly.

I'm older; is it too late to start?

No. Randomized trials have shown that even aerobic exercise begun at an advanced age may be associated with favorable changes in measures such as hippocampal volume and memory. In older age, balance and strength work also reduces fall risk, preserving independence.

What are BDNF and irisin, and why do they matter?

BDNF is a protein that supports the health of nerve cells and learning–memory processes; it increases with exercise. Irisin is a molecule released from muscle during exercise whose effects on metabolism and the brain are being investigated. These are possible pathways by which exercise may affect the brain; however, most of the data are at the animal and mechanistic level.

Does it also help mood and anxiety?

Regular exercise is associated with positive effects on mood and anxiety, and this is part of brain health. Our animal studies also point to the biological pathways by which exercise reduces anxiety; still, these findings are at the mechanistic level and do not replace clinical treatment.

Scientific references

Author's own work:
Uysal N, Yüksel O, Kızıldağ S et al. Regular aerobic exercise correlates with reduced anxiety and increased levels of irisin in brain and white adipose tissue. Neurosci Lett 2018;676:92-7.
Yüksel O, Ateş M, Kızıldağ S et al. Regular aerobic voluntary exercise increased oxytocin in female mice: the cause of decreased anxiety and increased empathy-like behaviors. Balkan Med J 2019;36(5):257-62.
Karakılıç A, Yüksel O et al. Regular aerobic exercise increased VEGF levels in both soleus and gastrocnemius muscles correlated with hippocampal learning and VEGF levels. Acta Neurobiol Exp 2021;81(1):1-9.
Gümüş H, İlgin R, Koç B, Yüksel O et al. A combination of ketogenic diet and voluntary exercise ameliorates anxiety and depression-like behaviors in Balb/c mice. Neurosci Lett 2022;770.
Other references:
Erickson KI, Voss MW, Prakash RS et al. Exercise training increases size of hippocampus and improves memory. Proc Natl Acad Sci USA 2011;108(7):3017-22.
Bull FC, Al-Ansari SS, Biddle S et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med 2020;54(24):1451-62.
Livingston G et al. Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. Lancet 2020;396:413-46.

This information is for general guidance only; it does not replace an examination, a diagnosis, or your physician's individual advice. Please consult a physician for your symptoms. About the author: Doç. Dr. Oğuz Yüksel — Academic Profile.