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Vol. 20, No. 1, 2021
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Áine Kelly is a physiology professor at Trinity College Dublin, who is particularly interested in exercise in relation to how the function of the brain changes with age. This article first appeared in

Being active, taking exercise, reduces in the long term your risk of development of for example, Alzheimer's disease. And what I'm interested in is understanding how exactly that happens.

Exercise is so important to general good health and good health of all of our organs. But there are several things additionally that it can do specifically for the brain that have an impact then on brain function in the long term. One of them is a process called neurogenesis, literally the birth and development of new neurons. It was thought for a long time that this didn't happen in the adult brain. That once we reached the age of full development that we couldn't develop any new neurons. And when the reports first came out about maybe 40 years ago or more that perhaps new cells could be developed in the brain, it was sort of dismissed because the dogma was that it just didn't happen. Now we have really good evidence that in fact, the adult brain does consistently produce new neurons throughout life.

So effectively you have stem cells in particular regions of the brain and given the correct stimulation, they are going to make more of themselves. And they're going to develop into mature neurons. That process only happens in a couple of discrete regions in the brain. And one of them is the hippocampus, which is very important for learning and memory. And it turns out that probably the best stimulus for neurogenesis in the brain is physical activity. So exercising directly results in the production of these new neurons within the brain, in regions that are important for learning and memory. And this perhaps then is the link between exercise and preservation of brain function, particularly memory throughout life.

There is also a link with mental wellbeing, stress and depression. It’s commonly understood that exercising regularly is a pretty good idea for your mood. And there could be a potential neurogenesis link here as well, because certainly in animal models antidepressants can stimulate the same kinds of molecular and cellular changes that exercise can in particular regions of the brain. Neurogenesis is being analysed in the context of diseases and disorders of the brain: Alzheimer's, Parkinson's disease, Multiple Sclerosis, and indeed even depression.

So as a therapeutic target, exercise can be employed as a preventative measure, or as sort of an adjunct therapy for some of these issues. But also if scientists like myself can understand the cellular, the fundamental biological basis of how exercise is doing this, then that might be a target for example, for drug therapies, for people maybe who can't exercise because of disability or, you know, fragility. There might be some kind of pharmacotherapy or a drug therapy that could mimic the effects of exercise on the brain. I mean, that, that's very aspirational and it's in the long-term, but it is a now a possibility.

In a recent article I wrote that exercising actually changes the structure of the brain, in particular the hippocampus region of the brain, that plays an important role in memory. A number of studies have used MRI scans to visualize the brain and look at the structure of the brain and that the volume of the brain. We know that some literal shrinkage of the brain takes place with age and that process is accelerated in Alzheimer's disease. Some studies have shown that taking regular physical activity can actually reverse some of that age related shrinkage of these particular brain regions. And that might very well be linked to this whole area of neurogenesis or being able to develop new neurons. On the large scale when we just think of the whole volume of the brain or indeed of particular brain regions, and that constitutes structural change.

One of the other things that we know happens with exercise is that it can stimulate the production of new blood vessels. This is something called angiogenesis. This happens in your muscles. If you work out and try to bulk up and increase the size of your muscles, you're going to have some growth of new blood vessels along with that, to support the new muscle tissue. Pretty much the same or a similar kind of thing can happen in the brain because we know that with exercise, new blood vessels develop in the areas where neurogenesis is taking place. So the blood vessel development and the development of new neurons are happening hand in hand. And this means that those newly born neurons will get the blood supply that they need to survive and to function properly.

Inflammation is another issue that is being implicated in many diseases.

The immune system is fascinating because it's so complicated and is consists of so many different cells and different areas of the body that can secrete different molecules. When we think about physical activity and exercise, we have to think of the flip side of that, which is being sedentary. And not being active is the source of lots of problems in the body. And particularly at the moment when a lot of us are kind of confined a bit more to our houses and we're not moving around as much as we normally do.

Being sedentary increases the risk of obesity, type two diabetes, certain forms of cancer for example. That again is linked to the immune system because it (sedentary behaviour-poor diet) creates an inflammatory environment within our tissues. That inflammation is linked to some of these conditions. And when we think of the brain, it's linked to age-related neurodegeneration such as Alzheimer's.

But the good news is that moving counteracts that. Exercise acts as an anti-inflammatory. It can pro-actively counteract pro-inflammatory events or pro-inflammatory changes that happen due to sedentary behaviour. As such, it is able to modulate the function of the immune system to take anti-inflammatory response. And we know some of the cell types that are involved as well as the biology of those cells and how they act. Exercise is able to change the function of those cells from being chronically pro-inflammatory to being anti-inflammatory.

As to frequency and intensity of exercising, we don’t yet have specific guidelines as it concerns optimal health for the brain. But we are generally recommending that adults engage in 150 minutes of moderate exercise per week or 75 minutes of vigorous activity. And then we need to do things that will build strength and flexibility as well.

For children it's an hour per day. We know that children in particular school children are not meeting the physical activity guidelines, which is a major worry for things like cardiovascular health and metabolic health, but also potentially for brain health, because in some of the studies that are coming out, at least in animal models, it seems that early life exercise, and this is something that I'm interested in working on myself, even if you are sedentary later in life, has protective benefits. So we really need to be active, particularly when we are younger.


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