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Does exercise have any effect on dementia or Alzheimer’s disease?


A lot of people are claiming that exercise improves cognition and reduces the risk of dementia or Alzheimer’s disease. As usual, these types of claims are based on one study, regardless of its quality.

A new study has been published that reviewed the body of evidence regarding the effect of exercise on cognitive decline, such as dementia. Exercise may have outstanding benefits for cardiovascular health, but this review seems to show that it may have no effect on cognitive function.

As I usually do, let’s take a look at the study and critique it.

elderly woman in gray tank top and leggings exercising
Photo by Wellness Gallery Catalyst Foundation on Pexels.com

Exercise and dementia study

In a study published on 27 March 2023 in Nature Human Behavior, Luis Ciria, Ph.D., of the Mind, Brain and Behavior Research Center, University of Granada, Granada, Spain, and colleagues analyzed the primary randomized controlled trials (RCTs) that made up the 24 meta-analyses that examined potential links between exercise and cognitive function, dementia, and Alzheimer’s disease.

Here is what the researchers found:

  • The meta-analysis of all the primary randomized clinical trials included in the revised meta-analyses shows small exercise-related benefits (d = 0.22, which is statistically insignificant).
  • The differences became substantially smaller after accounting for key moderators (d = 0.13)
  • The differences became negligible after correcting for publication bias (d = 0.05). Publication bias is defined as a bias in the published literature, where the publication of research depends on the nature and direction of study results. In other words, researchers may publish positive results but not negative ones, so the research is biased toward positive results only.

There are several reasons why exercise may only show a small to no change in cognitive health. First, in randomized clinical trials, the researchers may make the exercise group do a type of exercise that they don’t enjoy. If the participants enjoy a particular activity, they may care more about it, become more committed to it, and spend more time and effort to get better at it. This type of exercise may show benefits to cognitive health and executive function.

Second, randomized clinical trials focus on exercise alone. However, the benefits of exercise may be enhanced by the social and emotional aspects that could have benefits to cognitive and executive function.

Third, participants may be put into a trial that focuses only on one type of exercise, and some portion of the participants are not interested in it. In other words, a clinical trial that allows the participant to choose the exercise that they enjoy could show results such as a reduction in the risk of dementia and Alzheimer’s disease.

Finally, if the type of exercise employed in the clinical trial requires an instructor, the quality of that instructor could have an impact on the enjoyment of the exercise.

Controversy about exercise and cognitive function

Some scientists disagreed with the findings in the umbrella review that I discussed in the previous section.

Eef Hogervorst, Ph.D., director of dementia research and professor of Psychology at Loughborough University, Loughborough, England, and her Ph.D. student, Ahmet Begde, wrote that the umbrella study combined studies that were so dissimilar, meaning heterogeneity was very high, that it would lead to small differences. In other words, the studies were combined in such a way that “they did not show robustly that physical exercises do have a small, positive effect on cognition.”

However, many studies have shown that exercise is linked to small, but statistically significant, improvements in cognitive function. Frankly, even if there is a small improvement in reducing the risk of dementia or cognitive decline from exercise, it might be worth it.

In addition, a clinical trial is underway that will include 648 cognitively normal adults aged 65 to 80 years. They will be randomized to one of three groups: aerobic exercise for 150 minutes per week for 12 months; aerobic exercise for 225 minutes per week for 12 months; and active control of toning and stretching. The researchers will use MRI, blood markers, and positron emission tomography to look at beta-amyloid and some blood to look at tau protein -— precursors for the plaques and tangles that are observed in Alzheimer’s disease.

This study may tell us a lot more about the link between exercise and cognitive function, and the reduction of risk of dementia and Alzheimer’s disease.

Summary

This new study is far from perfect, and it may have unnecessarily put a lot of confusion into the link between exercise and cognitive function. It seems to show some problems with the clinical trials that have been used to determine if there is a link, but it did it in a way that may have introduced bias when they were trying to eliminate it.

I think the body of research still shows that regular exercise is linked to a lower risk of the development of dementia and Alzheimer’s disease.

The study that I reviewed seems to have a lot of weaknesses and other issues brought up by other researchers in this field. Thus, I have to give this study only two out of five stars. Usually, these types of reviews are supposed to be at the top of the hierarchy of biomedical research. That’s why scientists always review one another because sometimes the research just doesn’t agree with data that has already been published.

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Michael Simpson

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