It is exercise alone that supports the spirits, and keeps the mind in vigour.
Cicero
FOR MANY, THE top seed in the race for lifestyle interventions is exercise. This is somewhat surprising considering the lack of hard evidence. But there’s an intuitive logic here that is somehow hard to dismiss. Suffice to say, the overall health benefits of physical activity are considerable. Even moderate exercise can markedly lower blood pressure and improve cardiovascular health. And it is these resulting rewards that are thought to directly affect Alzheimer’s risk.
Having high blood pressure in middle age, for instance, puts one at higher risk of Alzheimer’s.1 Conversely, if one’s blood pressure is too low, especially over the age of seventy-five, the chance of Alzheimer’s still increases.2 Why? That’s unclear. Most evidence points towards a link between blood pressure and inflammation (again involving microglia), but exactly how this feeds into the whirlwind of plaques, tangles and brain calamity remains an enigma.
What is conclusive, in lab mice at least, is that exercise on a treadmill can reduce the build-up of plaques and tangles.3 This modest miracle is thought to happen by activating an intriguing cellular phenomenon called autophagy (Greek for ‘eating of self’), a specialised kind of cellular housekeeping that clears out damaged or unwanted goods and introduces new ones after recycling the old, all as part of an adaptive and protective process to help neurons better cope with stress and extend their lifespan. So it’s thought that stimulating autophagy through exercise may halt the progression of brain cell death in Alzheimer’s.
To take the molecular parlance a step further, a protein called BDNF (brain-derived neurotrophic factor) is the leading actor in this subplot. In December 2010 researchers at the University of Pittsburgh, Pennsylvania, recruited 120 people with an average age of sixty-seven and had them perform either moderate aerobic exercise or simple stretches three days a week. Strikingly, follow-up MRI scans revealed that those who exercised netted a 2 per cent increase in the size of their hippocampus.4 That isn’t bad considering that 1.5 per cent shrinkage is normal for this age. And the middleman in this small victory, it appeared, was BDNF: a molecule known to promote the birth of new neurons and synapses throughout the entire nervous system. BDNF has such potent effects on neurons, moreover, that pharmaceutical companies now view it as a good drug candidate, causing some scientists to whimsically grant it the rather droll nickname ‘brain fertiliser’.
Such a wonder is, sad to say, perhaps decades away. So in the meantime we must resolve not only to exercise but also to learn what kind of exercise and how often it’s required to keep the mind fit. The most thorough investigation of the subject so far–a systematic review entitled ‘The effect of exercise interventions on cognitive outcome in Alzheimer’s disease’ by researchers at the University of Sussex, England, in 2014–could find several methods demonstrating positive effects on cognition in Alzheimer’s patients.5 They ranged from thirty minutes of walking (four times a week for twenty-four weeks), to one hour of cycling (three times a week for fifteen weeks), to thirty minutes of vigorous calisthenics (every day for twelve weeks). For those who have reached an age where even walking is a chore, gentle movements, such as those practised in the Chinese martial art Tai chi, were also deemed worthwhile.
The fact that both high- and low-intensity exercise appears to help speaks volumes. Larger studies are still needed to unequivocally prove a link with Alzheimer’s, and this certainly doesn’t mean that someone can avoid the malady simply by working out. This brand of science–epidemiology–dispenses truths about millions, not individuals. Indeed, my grandfather’s quotidian hike lasted two hours. But still, a little exercise is probably worth it.
Naji Tabet, chief author in the investigation and a lifestyle research front-runner, emphasised this point when I spoke with him on the telephone. ‘You do not have to run marathons. You do not have to go to the gym three or four times a week. A brisk walk will do!’ Tabet decided to focus on exercise as a way to prevent Alzheimer’s out of desperation more than anything else. ‘When you see an illness that robs someone of their personality, their individuality, an illness that ravages their life and the life of their loved ones, you have to treat it in whatever way you can.’
Tabet has looked at what fitness fanatics call Ultra Vets, people in their seventies or eighties who exercise religiously. (I’ve worked in a lab with someone who fits that description; he was eighty-two years old, had not retired, and had just trekked across the Antarctic.) When Tabet compared a group of Ultra Vets who had no memory problems with an age-matched group of people who do what you or I would say is a normal amount of exercise, he found no difference in cognitive skills between the groups. ‘So if you overdo it,’ he said, ‘there’s diminished returns. Just do low-intensity exercise. Keep the heart going, keep the muscles going, keep the respiratory system going. Even a couple of minutes a day might protect you.’
But still I wondered, how is this possible? ‘Nobody knows exactly how it works,’ Tabet granted. ‘My feeling is that exercise helps the immune system fight the build-up of plaques and tangles. But exercise also helps the mood. And we know that people who are depressed are more at risk of Alzheimer’s, so it might have an indirect effect by simply making somebody feel better.’
Fantastical though it might sound, Tabet also thinks that mild exercise can go a step further than prevention. He believes it may actually slow the decline of Alzheimer’s in late-stage patients. He insists that activities as simple as throwing a ball around, gently moving the arms and legs, stretching–anything, in other words, that meets his explicit and unadorned message to ‘keep things going’–will do something.
With that, remaining positive, I moved on to rediscover a different form of exercise altogether.