The number of people with dementia is set to double in the next 20 years, so the importance of physical activity in preventing memory loss cannot be over-stressed, writes Margaret Jennings.
For years research has pointed to the healthy pay-off of exercise, with it commonly tagged in the media as ‘the magic pill’ for ageing well.
The benefits are indisputable — increased flexibility, balance, muscular strength, stress relief, and reduced risk on manyage-related diseases, to name just some.
But can exercise stave off memory loss — one of the top fears we have around ageing — as ongoing studies suggest?
With the number of people with dementia in Ireland expected to more than double over the next 20 years — from 55,000 today to 113,000 in 2036 — as an increasing number of us living into much older age, we could indeed do with such a ‘magic pill’.
However, nothing is that simple, of course.
The latest World Health Organisation (WHO) guidelines issued last month list getting regular exercise, as one of the lifestyle factors influencing risk reduction of cognitive decline and dementia, but it is a multi-factorial approach; the list also includes abstaining from smoking, avoiding harmful use of alcohol, controlling weight, eating a healthy diet, and maintaining healthy blood pressure, cholesterol and blood-sugar levels.
On the physical activity front, the WHO report favours aerobic exercise as being the most beneficial for affecting cognitive health, points out Dr Suzanne Timmons, consultant geriatrician and clinical lead for the national dementia office.
“The strongest evidence seems to be at the moment for aerobic exercise, which makes us think that it’s due to that good, healthy, blood-vessel supply to your brain,” says Timmons.
“We know that what is good for your cardiovascular health is good for your mind. There is now, overall, quite good evidence that exercise improves cognition in healthy, older people, which contributes towards cognitive reserve,” she says.
Cognitive reserve refers to our brain’s ability to change the way it operates and make added resources available to cope with challenges in life.
“We talk about brain reserve — how big and healthy your brain is — but cognitive reserve is about how your brain works.
"If you have a large, well, blood-supplied brain, then your reserve, if you do develop dementia, is significant.
"Their brain can compensate better and so they won’t develop symptoms and won’t have difficulties with their activities of daily living until later. Their brain is overall so healthy, that other parts of the brain can take over a little bit."
However there isn’t yet strong evidence to say that exercise reduces your risk of dementia or mild cognitive impairment and to date there is no conclusive evidence that exercise will slow the rate of progression from mild cognitive impairment to dementia, she adds.
“It is also important that we don’t just take exercise in isolation.
"A 2017 multi-domain intervention study, for instance, shows the need to target the whole package and you may only need a very small benefit in each [lifestyle] domain when you put them all together to have a beneficial effect,” says Timmons.
On the lifestyle front, we are not doing particularly well with exercise, though, as an ageing nation.
Over two thirds (67%) of people aged 50-plus, report low levels of physical activity, according to The Positive Ageing 2016 National Indicators report.
As we increasingly lead sedentary lives, it’s vitally important that we get moving for healthy ageing, say Dr Ruth McCullagh, a lecturer in physiotherapy, and Trish O’Sullivan, a clinical practice tutor in that discipline, both in the School of Clinical Therapies at UCC.
Along with acknowledging the role of aerobic exercise, they both refer to studies which emphasise the importance of adding a “cognitive component” to the physical routine, to enhance memory function.
“While the aerobic has an impact and the cognitive challenges have an impact, it has been found that doing both simultaneously, has a better effect on your cognition,” says McCullagh.
"It can also be got from simply engaging in conversation with others while out walking, but if a teacher, for instance, uses the same exercise all the time at the gym, then your cognitive load lessens,” she says.
“It has to be something that you need to concentrate on, to achieve a task, while exercising aerobically. It really does improve the person’s overall ability to complete complex tasks.”
O’Sullivan, who works with people with dementia at the mild-to-moderate stages and is invested in the importance of exercise in that stage of the disease, says her profession is trying to encourage GPs to referpatients to physiotherapy to help in slowing down cognitive decline.
Regarding the cognitive component she says: “I would also encourage patients to do their exercises in different environments, not just on their couch, for instance, but to do it in a bench in the park, or off different heights, or using different chairs, forinstance, so they are getting that cognitive load.”
We all age differently and the question of why some people’s brains are more resilient to others will be impacted by our genes, says Áine Kelly, associate professor in physiology in TCD, whose main research interest is in the effect of exercise on the brain.
“We know the brain is incredibly plastic and is constantly changing, and learning and memory have physical underpinnings; the cells physically can change, and one of the things that contribute towards that neuroplasticity is exercise,” she says.
The tools generally used to measure memory function in studies are cognitive testing and MRI scans.
Human brains can’t be biopsied but Kelly works as a neuroscientist largely with animal models, which enables her to access those particular structures, or expression of different proteins or cell alteration, in relation to ageing and exercise activity, to understand the biology underneath the change.
“We see that physical activity can stimulate the production of new neurons within the animal brain — it’s called neurogenesis — so it’s the concept that by maintaining this neurogenic capacity throughout life, the physical structures remain healthy and promote plasticity.”
In the context of neurogenesis, the biological processes she is exploring are the health of the blood vessels of the brain and the blood flow in the brain and the connectivity between neurons and the way the synapses develop, to see if it can be really understood at a cellular level how this it is happening.
“There are lots of these different types of studies being carried out worldwide building data and, broadly, it seems that physical activity is beneficial to cognitive function, but we still don’t know how much exercise, how intensive it should be, and how often, because what we need are very large long-term studies involving huge numbers of different people — such as has been more prevalent in the cardiovascular literature, for example — to get a biologically meaningful result, but I think that will happen over time,” says Kelly.
“When looking at animal studies, it’s looking at a particular species and the biological variation is reduced, and also we can prescribe exactly how much exercise they are getting, all these biological variations, but when working with humans, it’s messy, because everybody is different, everybody has different backgrounds,different life experiences, and so on.”
It’s obviously important that biologicalinsights of animals can be translated toinvestigate biological changes that might also be meaningful in humans.
One such example is the discovery that BDNF (Brain Derived Neurotrophic Factor) a protein which has been tagged “fertiliser for the brain”, because it supports neurons and helps new ones to grow, is increased in animals when they exercise.
“In human populations, you can’t look at it in the brain of a living subject, but we have taken samples and what we have found, and others have found, is that exercise stimulates the circulation of this protein in the blood and we don’t know directly what effect that might be having on the brain, but we know from the animals that expression of BDNF protein is correlated with cognitive outcomes and so on,” says Kelly.
Also, within animals, it is known that BDNF is involved in plasticity within the brain at a cellular level. “So again we are extrapolating and that’s why it’s beinginvestigated in humans,” she adds.
As all this cutting-edge work on exercise and the brain is being carried out, we will continue to be drip-fed new outcomes from studies, such as this latest one which found that a single session of acute exercise benefitted semantic memory (such as memory of life events and factual processes) in older adults.
But, as many scientists in the field conclude, translating the promise of physical activity to human memory improvement has been challenging and the best modes of activity and cognitive outcomes remain unclear.
In the meantime, however, there is no argument regarding how essential all forms of exercise is for our body and mind as we age — that if we don’t use it we lose it.