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 www.greenmedinfo.com
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.
