How exercise can help prevent Alzheimer’s disease | NOVA
Your brain loves it when you exercise. Sure, you might not like every sweaty minute of your kickboxing class or your Saturday afternoon run yourself, but your brain relishes it. That’s because exercise doesn’t just increase muscle tone. It doesn’t just boost energy levels and improve mood, fighting depression and anxiety. It also strengthens problem-solving skills and memory. And, research has increasingly shown that it protects against Alzheimer’s disease, both by delaying the onset of the disease and slowing the decline in patients already diagnosed.
As baby boomers age and more Americans live longer, Alzheimer’s disease is on the rise. In 2020, some 5.8 million people in the United States were living with this most common form of dementia, in which inflammation and tangles of malformed proteins in the brain accompany progressive memory loss and the inability to think. carry out daily tasks.
Despite decades of research, effective treatments for Alzheimer’s disease have eluded researchers; even a full explanation of what goes on in the brain of a patient with Alzheimer’s disease has remained out of reach. That’s partly because the disease is incredibly knotty and multifaceted, says Fang Yu, a researcher at Arizona State University who specializes in applying new dementia science to human trials. Alzheimer’s disease affects a myriad of processes in the brain, our most complicated organ, but most treatments developed so far have only been able to tackle one aspect of the disease at a time, she says. “Even if there is a drug that can help target certain pathways, many pathways are needed.”
This is why Yu’s studies of Alzheimer’s disease have often focused on the power to move our bodies. Exercise is unique in that it also affects the body and brain in many ways, she says, making it an important intervention for addressing the complexity of Alzheimer’s disease.
It’s “something pretty special,” says Christiane Wrann, a neuroscientist at Harvard University and Massachusetts General Hospital. While you’re dancing, biking, or running, it may seem like “you’re doing something that has nothing to do with the brain,” she says. “But you actually get an improvement in cognitive function.”
How it works?
Perhaps the easiest way to exercise to guard against Alzheimer’s disease is to improve cardiovascular health. The effects of a good sweating session do not stop at our heart, they also help to improve the condition of our other organs and blood vessels. These healthier vessels improve connections between brain cells called neurons, Wrann explains. With reinforced wiring, it’s easier for nourishing oxygen to get in, for waste to get out, and for neurons to talk to each other. And better heart and lung fitness also appear to help the brain absorb glucose more efficiently, which helps keep neurons healthy.
Additionally, research on mice – a common, if imperfect, source of new Alzheimer’s disease science, since it is not possible to ethically conduct some types of research on human beings living – showed that exercise is a rare cause of “adult neurogenesis”, or the growth of new neurons in adulthood. While it’s hard to fully prove the same thing happens in humans, a key player appears to be irisin, a hormone made in muscles in response to exercise, Wrann says. Irisin is special because it carries a passageway to cross the blood-brain barrier, the barricade of tissues and blood vessels that prevents harmful substances from reaching the brain.
Once inside, irisin helps the brain create a neurotransmitter called BDNF, which is important for hippocampal health. The hippocampus is a center of learning and memory in the brain, and the hippocampi of Alzheimer’s patients tend to shrink as their health declines, Yu says. in the hippocampus and pruning connections that are no longer needed – two processes supported by BDNF – is essential to stabilize and protect it.
A series of studies at Wrann’s lab in Boston have also shown that, at least in mice, irisin produced during exercise has potent anti-inflammatory effects in the brain. This could be an important insight because some new research points to inflammation, rather than previously implicated amyloid plaques, as a possible cause of neuronal death in Alzheimer’s disease. Inflammation is caused by the immune response to negative stimuli, not just viruses or bacteria, but also, for example, misfolded proteins in the brain. In an Alzheimer’s patient, the immune system may react to the presence of these plaques by attacking them, Wrann explains, and in his excitement may also attack the synapses that connect neurons. “If it gets completely out of control, you have this ‘friendly fire’ that damages neurons,” she says. But his research indicates that irisin can bind to receptors on specialized cells deep within the brain, calming this inflammatory response.
And one final piece of the puzzle is sleep — not a type of exercise per se, but caught up in a sort of love triangle with exercise and Alzheimer’s disease. When it comes to preventing dementia, sleep and exercise can work together, says neuroscientist Miranda Chappel-Farley, Ph.D. candidate at the University of California, Irvine. Studies have shown that more exercise leads to better quality sleep, which itself is an important protective factor against Alzheimer’s disease. And people who sleep better are more likely to feel ready to exercise. Together, they create a powerful bulwark against dementia and are a lifestyle factor ignored at your peril, says Chappel-Farley, who cautions against “focused exercise but disregard sleep.”
What type of exercise is best?
Aerobic exercise appears to be the champion when it comes to protecting against Alzheimer’s disease and maintaining executive function. Sure, most mice in Alzheimer’s trials roll on their wheels, but that doesn’t mean you have to. Cycling, dancing, swimming, or any other activity that gets your heart rate up is a good candidate, Yu says. That’s because it has the potential to raise BDNF levels; stimulate blood flow and strengthen blood vessels; and decrease “white matter hyperintensities,” abnormal changes that affect how the brain transmits electrical signals.
More recent research also indicates that resistance-based muscle-strengthening exercises can support a wide range of cognitive functions. This effect looks particularly promising in patients who have already been diagnosed with Alzheimer’s disease, where it may help slow their decline, adds Yu, who often works with dementia patients. Here, the objective is not improvement but the slowing down of deterioration. “And that’s basically what my research has shown: this exercise can level and stabilize,” she says.
Tai chi and other types of movement that incorporate mindfulness also reduce stress and inflammation and improve sleep, she adds. And some research suggests that a mix of several types of exercise can provide greater improvement than a single activity. In a review of 71 studies on exercise and dementia, Yu and her colleagues found that the most effective exercise was the “mixed component,” a mix of muscle-strengthening and aerobic workouts.
Still, “it’s important to point out that there’s a lot we don’t know yet,” says Chappel-Farley, because exercise comes in many forms and can be adjusted for duration, intensity, frequency and timing. “It’s not entirely clear which might be best.” Does it take a certain amount of exercise for our brain to reap the benefits? Are there any findings in extensive mouse research on this topic that cannot be transferred to humans?
Wrann says the data is encouraging so far, indicating that the more you exercise, the more benefits you’ll get. And really, what is the risk? “My big message is that exercise is good for you,” Yu agrees. “Even if in the future we find that it doesn’t prevent Alzheimer’s for everyone, it’s still good health and quality of life.”
But Wrann also remains mindful of people who can’t exercise due to disability or physical limitations, or who can develop Alzheimer’s disease despite lots of exercise; there is still no magic bullet for dementia. While it’s unlikely researchers can develop a drug that can affect the body in as many ways as exercise, she’s hopeful about irisin’s potential as a source of new drug therapies. Because it’s a powerful anti-inflammatory that can already cross the blood-brain barrier, she wonders if it would be possible to use irisin to create a drug that even goes beyond the positive effects of irisin. exercise. Inflammation in the brain appears to be at the heart of many neurological diseases. That way, she says, “we could reach people with Alzheimer’s disease or beyond.”