Tue. May 24th, 2022

Physical activity is very important for a number of reasons – including that it helps to protect the structure and function of our brain as we get older. This may be the key to reducing the risk of developing certain neurodegenerative conditions, such as Alzheimer’s disease.

Although researchers have known about the protective effect of exercise for many years, exactly why it has this effect on the brain has remained a mystery. But a recent study published in the Journal of Neuroscience may shed some light on this puzzle. According to its results, physical activity alters the activity of the brain’s immune cells, which lowers inflammation in the brain.

The brain contains a class of special immune cells known as microglia, which constantly examine brain tissue for damage or infections and remove dirt or dying cells. Microglia also help control the production of new neurons (nerve cells in the brain that communicate and send messages to other cells) through a process called neurogenesis, which is associated with learning and memory.

But in order for microglia to step up and perform their work, they must switch from a resting state to an activated state. Signals from pathogens (such as a virus) or from damaged cells will activate microglia. This changes their shape and causes them to produce pro-inflammatory molecules – allowing them to resolve and repair damage or infections.

However, microglia can also be activated inappropriately as we get older, causing chronic encephalitis and impairing neurogenesis. This inflammation has been suggested as a reason why brain function often decreases with age, and these changes can be even worse in the case of neurodegenerative conditions such as Alzheimer’s.

Studies in laboratory mice and rats have shown that exercise can counteract some of the harmful effects of microglial activation. But this latest study has for the first time revealed a link between physical activity, reduced microglial activation and better cognitive function in the human brain.

The study’s researchers looked at 167 men and women who participated in the Rush Memory and Aging Project. This is a long-term project at Rush University in Chicago that seeks to identify factors that contribute to the health of the brain in older people. Participants conducted annual assessments of their physical activity, which were monitored by a portable activity tracker along with assessments of their cognitive function and motor performance (such as muscle strength and walking speed).

Participants also donated their brains for post-mortem analysis as part of the study. This allowed the researchers to analyze the brain tissue for signs of activated microglia and for signs of disease in the brain – such as unhealthy blood vessels or the presence of plaques containing the protein beta-amyloid (a hallmark of Alzheimer’s disease). The researchers also looked at the levels of synaptic proteins in participants’ brains. Synapses are the small nodes between nerve cells where information is transmitted, so the levels of these give a broad indication of healthy brain function.


On average, participants were 86 years old when their physical activity began to be monitored, and about 90 years old when they died. About one-third of the participants had no cognitive impairment, one-third had mild cognitive impairment, and one-third had been diagnosed with dementia.

However, post-mortem analysis revealed that about 60% of participants actually had signs of Alzheimer’s disease in the brain (such as amyloid plaques). This shows that the presence of typical signs of Alzheimer’s disease does not necessarily mean that a person will show major symptoms of cognitive impairment while alive.

A digital depiction of amyloid plaques that form between neurons in the brain.
More than half of the participants showed signs of Alzheimer’s in the brain, such as amyloid plaques.
nobeastsofierce / Shutterstock

It is not surprising that the younger the participants were, the more physically active they were and the better their motor function. In general, being more physically active was associated with lower microglial activation in certain regions of the brain (such as the inferior temporal gyrus, which is involved in memory and recall), which is typically affected early on when Alzheimer’s begins to develop.

This was true even when signs of Alzheimer’s were present in the brain. This suggests that physical activity can reduce the damaging effects of inflammation in the brain – even when a disease has already begun to develop. The study also showed that more microglial activation was associated with greater cognitive decline and lower synaptic protein levels.

These findings not only indicate that inflammation in the brain can significantly affect cognitive function and may be a risk factor for the development of Alzheimer’s disease, they also show that physical activity can help us develop resistance in the brain to effects that would otherwise be harmful. .

Read more: Five activities that can protect your mental and physical health as you get older

Although these results are promising, there are some limitations to the study. Post-mortem analysis can only reveal a single snapshot of brain status. This means that we can not say exactly when signs of illness developed in the participants’ brains – and at what point physical activity could have made a difference.

The study was also only observational, meaning that it observed changes in participants going on in their lives – unlike an intervention study where different people were randomly assigned to two different groups, where some trained and some did not. We can therefore not conclude with certainty that physical activity directly caused the observed changes in brain tissue and cognitive function. Nor do these results explain the mechanism by which exercise induces these effects.

But this study still adds weight to the growing body of evidence that physical activity can protect brain health and function – even in old age. Being active throughout our lives is likely to give us the best chance of preventing Alzheimer’s and other neurodegenerative conditions from developing, and helping us to live long, healthy, and independent lives.

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