Does Exercise Protect Your Brain? What the Trials Show

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You have probably seen the claim that exercise is the closest thing we have to a pill for your brain. It is a catchy line. It is also more than the research supports. The studies point in a hopeful direction, and some of them disagree with each other. Here is what the authors report, and what that means for a Tuesday morning walk.

What the best known trial found

The study people cite most often is a randomized controlled trial by Kirk Erickson and colleagues, published in the Proceedings of the National Academy of Sciences in 2011. The authors report that in 120 older adults, aerobic exercise training increased the size of the anterior hippocampus, a region involved in memory, and that this came with improvements in spatial memory.

The authors describe that 2 percent gain as effectively reversing age related volume loss by 1 to 2 years. In their comparison group, hippocampal volume declined. They also report that people who started with higher fitness lost less volume, and that larger hippocampal volume was linked with higher blood levels of BDNF, a protein involved in the growth of new brain cells in animal research.

Two cautions belong here. First, this is one trial. A single randomized study is a strong signal, but it is not a settled fact. Second, the main finding is about brain structure and a spatial memory test. It does not tell us whether people who exercise are less likely to develop dementia years later. We did not find that outcome in the trial abstract, so we are not claiming it.

What the larger reviews say

When researchers pool many trials, the picture gets more mixed.

Joseph Northey and colleagues reviewed trials of exercise and cognitive function in adults older than 50 and published the results in the British Journal of Sports Medicine in 2018. The authors report that physical exercise improved cognitive function, with an average effect of 0.29 (95% confidence interval 0.17 to 0.41). Aerobic exercise, resistance training, multicomponent training and tai chi all showed significant benefits. Sessions of 45 to 60 minutes at moderate or higher intensity gave the strongest improvements. The authors recommend that clinicians advise people over 50 to do both aerobic and resistance exercise at moderate intensity on as many days of the week as feasible.

That is encouraging, and the average effect is modest.

A Cochrane review by Juliana Young, Maaike Angevaren, Jennifer Rusted and Naji Tabet, published in 2015, looked at aerobic exercise in older adults without known cognitive impairment. It included twelve trials with 754 participants. The authors report that they did not find significant benefits of aerobic exercise or increased fitness on any aspect of cognition. They also report that all of the trials were at moderate or high risk of bias, which lowered their confidence in the findings, and that exercise may still help particular subgroups. They called for more research.

Put those side by side. One review found a modest benefit across several kinds of exercise. Another found no benefit from aerobic exercise alone in healthy older adults, with weak underlying trials. The reviews cover different questions, different exercise types and different trials, so they do not have to be in conflict. They do tell us that "powerful intervention" is too strong a description.

How much should you do?

No trial we read gives a proven dose for brain health. What we can point to is the World Health Organization 2020 guideline for adults. It recommends 150 to 300 minutes of moderate intensity aerobic activity a week, or at least 75 to 150 minutes of vigorous activity, plus muscle strengthening on 2 or more days. For adults 65 and older, it adds balance and strength focused activity on 3 or more days a week. These targets come from general health research. They are a sensible default, and the Northey authors' advice points the same way: moderate intensity, mixing aerobic and resistance work, sessions of 45 to 60 minutes.

Moderate intensity means you can talk but you cannot sing. A brisk walk, cycling, swimming or dancing all fit.

If you are starting from zero

We did not find a trial that tells you what the first rung of the ladder should be, so we will not claim that a particular amount "dramatically" helps. A reasonable reading of the guideline is to build toward it. Start with walks you can repeat, add a day when the habit feels easy, and add strength work once walking is routine.

Based on the Erickson and Northey findings, one way to act on them is to make the behavior easier to repeat. That could mean a book that explains the science and keeps you motivated, which is the option below. We rate the behavior of regular exercise, not any particular book.

The bottom line

Exercise has good reasons behind it for your heart, your mood and your independence as you age. For your brain, the trials suggest it may help, and the best reviews disagree on how much. Treat it as a smart bet, not a drug. If you notice memory changes that worry you, talk with your doctor. This article is for education and is not medical advice. Check with your healthcare provider before starting a new exercise program, particularly if you have a health condition.