It has long been accepted that exercise cuts the risk of heart disease, and recent studies suggest a raft of more general benefits, such as reducing the risk of certain types of cancer and even preventing the onset of Type 2 diabetes. Now it seems gym junkies also can expect a boost in brainpower, too.
This is not just the vague glow of well-being suggested by sayings such as “a sound mind lives in a healthy body.” John Ratey, a neoropsychiatrist at Harvard Medical School and others are finding that fitness has a long-term influence on a wide range of cognitive abilities. Physical activity seems to be important during childhood, powering the brain through the many changes that help us to mature into adulthood. But it may also play a role as we reach advanced age, with a decline in fitness explaining why some people are more prone to dementia than others.
“It’s a really amazing effect,” says David Raichlen, a biological anthropologist at the University of Arizona in Tucson. Raichlen is investigating whether our ancestors’ athleticism may have accelerated the evolution of their intelligence millions of years ago. Our brains may, in fact, be a byproduct of our brawn.
The link between fitness and the performance of simple cognitive tasks was first suggested by studies in the 1960s, but its importance became more greatly appreciated about 30 years later.
In the 1990s, Fred Gage, a geneticist at the Salk Institute in La Jolla, Calif., found that exercise seemed to cultivate the growth of new neurons in mice. At about the same time, Arthur Kramer, a cognitive psychologist at the Beckman Institute for Advanced Science and Technology at the University of Illinois, published a paper in Nature showing that previously sedentary adults who undertook an aerobic fitness plan for six months boosted their performance in cognitive drills that required executive control. That’s the kind of concentration that helps you to switch between different tasks without making mistakes, and it is a key contributor to more general intelligence.
A spate of later papers tracked people’s fitness and cognitive skills over several years, sometimes decades. Initially, most of the investigations examined older people whose mental abilities were expected to diminish with age. One German study, published in 2010, tracked 4,000 people older than 55 for two years. It found that those who rarely took part in physical activities were more than twice as likely to suffer from a cognitive impairment by the end of the study than those who engaged in exercise such as gardening, swimming or cycling a few times a week.
Another study, which had followed a group of nearly 1,500 people for 20 years, showed that these effects may be long-lasting. Those who exercised at least twice a week during middle age were much less likely to develop dementia by the time they reached their 60s and 70s, even when potentially confounding factors such as education, drinking and smoking were taken into account.
Although there are fewer studies of younger people, the available evidence suggests that physical activity enhances brain health at every stage of life. Some of the most striking statistics concern schoolchildren in New York. Students in the top 5 percent of the fitness rankings scored 36 percentile points higher on standardized academic tests than students in the bottom 5 percent. Similar results come from the records of 1.2 million men who enlisted for military service in Sweden between 1950 and 1976; these data allowed researchers to compare the men’s physical education grades at 15 with their cardiovascular performance at 18. Changes in fitness during these teen years seemed to correlate with the young men’s intelligence scores and cognitive abilities by the end of that period.
What’s behind the link? A short-term mood boost might be bringing some of the benefits.
“People really enjoy that euphoric aspect of a runner’s high and the clarity of mind you get from a routine workout,” says Brian Christie, a neuroscientist at the University of Victoria in British Columbia. Stress can inhibit your brain’s responses when solving a problem, blocking it from making the necessary connections. “If you go out for a walk, your stress levels usually plummet. And that’s when the answer comes to you,” Christie says. That may partly explain why fitter children tend to do better at their schoolwork, for instance.
Exercise probably contributes to more-permanent changes, too. The brain relies on a steady supply of nutrients and oxygen through an intricate network of capillaries. Physical activity can encourage the construction of these supply lines, and it also can ease their maintenance. Matthew Pase at the Swinburne University of Technology in Melbourne, Australia, has found that high blood pressure, particularly in the central large arteries that feed the brain, can lead to a slump in cognitive performance, perhaps because it damages those vessels. Since regular physical activity reduces blood pressure, it should protect the brain from this undue stress.
Improved fitness also cuts the risk of diabetes and obesity. These problems disrupt the brain’s insulin system, which is thought to trigger a cycle of reactions that contribute to the build-up of the plaques linked to brain damage in people with Alzheimer’s disease.
Exercise also has been found to spur the release of such neurotransmitters as serotonin, noradrenaline and dopamine, which help regulate signaling in the brain. These neurotransmitters are the same ones that antidepressants and drugs for attention-deficit hyperactivity disorder act on, which is why time on a treadmill or bicycle is akin to taking a mix of Prozac and Ritalin, Ratey says. It also prompts the brain to send out growth factors such as insulin-like growth factor-1 (IGF-1) and brain-derived neurotrophic factor (BDNF). Ratey describes BDNF as “Miracle-Gro for your brain” because it creates an environment where neurons can flourish and promotes the formation of new connections between cells.
The brain-enhancing consequence of exercise has serious implications today. The Department of Health and Human Services is encouraging schools to offer more physical education, and the Institute of Medicine recommends that elementary school children get 30 minutes of physical activity a day, 45 minutes daily for middle and high school students. “We need to have kids moving every day, not just because it makes sense health-wise, but because it raises test scores,” Ratey says.
The same principle applies to the older population and offers an alternative to cognitive training strategies, such as brain teasers, that are often touted as ways to sharpen the aging brain. There’s not a lot of evidence to back these up, Kramer says, since the improvements gained don’t seem to translate to everyday life. In contrast, new exercise regimes tend to accelerate processing speed and improve attention and memory in all kinds of activities.
What kind of exercise is ideal? An aerobic workout is essential, but it doesn’t have to be too strenuous. Kramer has found that even gentle activities, such as taking a walk a few times a week, worked wonders for some elderly volunteers, increasing the connectivity of their brain network and the size of their hippocampus and boosting overall recall.
For those who already are in good shape, Ratey advocates high-intensity interval training (HIIT), which consists of very short, very hard bursts of exercise. Pushing your body in this way triggers the pituitary gland to release human growth hormone, he says, which enhances neurotransmitter levels. As evidence for HIIT’s effectiveness, Ratey cites a German study in which participants incorporated two three-minute intervals of high-intensity sprinting into a 40-minute run. They produced much higher levels of BDNF and noradrenaline, and the runners performed 20 percent better in a post-run vocabulary-building exercise than those who had taken more leisurely exercise. However, Ratey cautions that HIIT is something that inexperienced exercisers should build toward slowly.
Ratey practices what he preaches, exercising at least three times a week for 20 minutes, with six 30-second high-intensity intervals in each session.
Kramer, 60, also exercises regularly; at work, he uses a standing desk and walks 30 minutes to an hour each day on a treadmill beneath it.
It’s never too late to begin getting these benefits, Kramer says. “I’m often asked: ‘If I’m 70, will it help me?’ The answer is: Absolutely, yes.”