If you want to avoid the cruel fate of dementia, then one of the best things you can do is to get on your bike or go for a jog.
Scientists have long known that exercise has a protective effect against Alzheimer’s disease as well as other dementias. Last year, the Alzheimer’s Society analysed the findings of 11 different studies that examined the connection between lifestyle changes and brain health in later life, and found that it was exercise which made the most difference.
While quitting smoking, maintaining a healthy weight, eating a balanced diet and avoiding alcohol can all mitigate dementia risk, none of these measures makes as much difference as regular exercise. Overall, Alzheimer’s Society researchers found that exercise alone cuts dementia risk by up to 45 per cent.
A new study in the peer-reviewed journal Neuron revealed a major new clue as to why this might be the case. Exercise releases a hormone called irisin, which is capable of clearing the toxic amyloid plaques in the brain that kill off nerve cells, causing Alzheimer’s disease.
“Irisin helps reduce these plaques,” says Christiane Wrann, an assistant professor of medicine at Harvard Medical School, who was involved in the study. “In previous studies, we’ve shown that cognitive decline is slower in mice engineered to have features of Alzheimer’s that have been treated with irisin. It seems that it might have effects on cognitive function, neuroinflammation, clearing plaques, and also encouraging the formation of new neurons in the brain.”
Michael Hornberger, a professor of applied dementia research at Norwich Medical School, says this is the first time that exercise has been shown to potentially reduce the accumulation of toxic proteins in the brain. “I think it’s very exciting,” he says. “It’s the first evidence that exercise can directly stop amyloid from congregating, which is important, although we need to see if the findings replicate in future.”
So what forms of exercise should we do and how much is required to keep our brains sharp as we age?
How does exercise reduce Alzheimer’s risk?
Irisin isn’t the only way exercise improves our brain health. One of the other main ways in which exercise reduces your risk of dementia is by improving cardiovascular health. In 2019, a study in the British Medical Journal found that people who still had excellent heart health at the age of 50 were much less at risk of dementia in later life, while in 2022 the University of Exeter reported that people who either had Type 2 diabetes, a stroke or a heart attack had three times the dementia risk.
“The old adage that what’s good for the heart is good for the brain, very much applies,” says Hornberger. “The reason is that the brain is using a huge amount of our blood oxygen and blood sugar because it’s so active, so we need a good blood supply to the brain.”
Some forms of dementia, such as vascular dementia, are even directly linked to impaired blood flow to the brain. Another study, from researchers at Lund University in 2019, found that middle-aged Swedes who skied or ran regularly were less likely to develop vascular dementia in old age.
But it’s not just about blood flow. According to Andrew Budson, professor of neurology at Boston University and author of the book Why We Forget and How to Remember Better: The Science Behind Memory, another benefit of vigorous exercise is that it releases a molecule in the brain called brain-derived neurotrophic factor (BDNF), which helps neurons regenerate and become active. In particular, this has been found to occur in regions important for memory, such as the hippocampus. Budson refers to a noted 2011 study which showed that 55 to 80 year olds who worked on increasing their fitness, saw a comparable improvement in BDNF levels, the size of their hippocampus, and their memory performance.
“Aerobic exercise releases BDNF. That helps existing neurons in the brain to survive and can actually promote the growth of new brain cells,” says Budson. “In that 2011 research, these individuals actually were able to increase the size of their hippocampus over time, and that’s the part of the brain that helps us to form new memories.”
Which type of exercise is best to reduce risk of Alzheimer’s and dementia?
Budson says any type of physical activity that elevates the heart rate, such as running, swimming, vigorous walking, cycling, or playing sports such as tennis, squash and badminton, will reduce your risk.
“Studies in people with mild cognitive impairment who started doing aerobic exercise and improved their cardiorespiratory fitness saw a slowing down in the progression,” says Wrann.
As such, walking the dog or going for a gentle stroll is unlikely to be sufficient to get the benefits that will truly protect the brain. This is about breaking a sweat.
“We make a distinction between activities of daily life, which we call physical activity,” says Wrann, “and exercise which is something you’re doing with the purpose of improving your fitness. It’s exercise where the evidence is strong for brain health.”
While strength training with weights is important for improving balance and preventing frailty, the jury is still out on whether it protects the brain. Some research has suggested that regular weightlifting over the course of a year leads to overall benefits in cognitive performance and may even prevent parts of the hippocampus from degenerating. But the findings are still preliminary.
“If you do strength training regularly and with repetition, that can elevate your heart rate,” says Hornberger. “And it also protects against stumbling and falls, which lead to hospitalisation, which in itself is not good for your brain.”
How much exercise do I need to reduce Alzheimer’s risk?
Aim to do some sort of aerobic exercise for at least 30 minutes per day, five days per week.
In terms of steps, Wrann points to a 2022 paper in the journal JAMA Neurology which showed that doing approximately 10,000 steps per day reduced the risk of developing Alzheimer’s by 50 per cent. The same study suggested that the minimum dose to achieve any benefit is around 3,826 steps per day, which still reduces dementia risk by 25 per cent.
However, it seems that these steps are best completed through more vigorous forms of exercise, like running or brisk walking, which improve your fitness levels.
Some experts say that as little as 10 minutes of high-intensity exercise is sufficient. However, Hornberger says that this isn’t suitable for everyone, particularly over-50s who have previously been largely sedentary.
“If you haven’t been physically active, I would be cautious about jumping into high-intensity training straight away,” he says. “I would first discuss with your GP about your general condition before doing so.”
A pill that delivers the benefits of exercise
In recent years, scientists have begun to hone in on the idea of an exercise pill, a drug aimed at relatively inactive older individuals that could be taken orally and would package some of the health benefits of doing regular exercise into a single capsule.
For a long time, this sounded more like science fiction than genuine research. But, just as weight-loss drugs like Wegovy and Ozempic are based on an artificial form of the GLP-1 appetite hormone, Wrann believes that a synthetic version of irisin could be used to create a future exercise drug.
Along with colleagues, she has now founded a company called Aevum Therapeutics, which is pursuing this exact goal. “We’re looking at exercise-based therapeutics for neurodegenerative diseases,” she says. “Irisin could be one of these drugs. It works on neuroinflammation and plaque clearance, which are both relevant for how Alzheimer’s disease works.”
Until that happens, Wrann suggests finding a form of exercise that you enjoy, particularly one that gets you sweating and your heart pounding. While the ideal amount is 30 minutes, five times per week, she says that even if you’re doing less, it’s definitely far better than nothing.
“Even if you can do 10 minutes per day, that will still be beneficial to your body and mind in some way,” says Wrann.