“I think the Diabetes Prevention Program was eye-opening for the medical community because it was one of the first large randomized controlled trials comparing a lifestyle intervention to a drug intervention,” says Wendy Kohrt, a professor of medicine and the Nancy Anschutz Chair in Women’s Health Research at the University of Colorado. Kohrt says the goal and hope of the trial was to show that lifestyle changes could match the clinical benefits of metformin. The fact that lifestyle changes vastly outperformed the drug — especially among older adults — was a shock, she says.
How does exercise help people with diabetes? A 2016 position statement from the American Diabetes Association summarizes the evidence on exercise and declares that both aerobic and strength training can significantly and rapidly improve measures of glycemic control and insulin sensitivity. “Physical activity creates muscle contractions, which allows the muscles to take up blood glucose directly without the need for insulin,” says Sheri Colberg-Ochs, first author of the position statement and a professor emerita of exercise science at Old Dominion University. “Exercise is like a separate dose of insulin that always works,” she adds.
Along with Type 2 diabetes, autoimmune disorders are among the most common causes of chronic disease in the U.S. The term “autoimmune” refers to medical conditions in which the human immune system inappropriately attacks healthy cells, nerves, or tissues. More than 80 conditions fall under the autoimmune disease umbrella, according to the NIH, and these include rheumatoid arthritis, lupus, celiac disease, inflammatory bowel disease, and multiple sclerosis. There’s evidence that rates of autoimmune diseases have exploded in recent decades. And while experts have struggled to determine the precise drivers of this unhappy trend, there’s strong evidence that exercise can relieve or ameliorate the symptoms of a diverse array of autoimmune disorders.
“In people with multiple sclerosis, we’ve made the case that exercise could be influencing the progression of the disease through at least three different pathways,” says Robert Motl, a professor and associate director of research at the University of Alabama, Birmingham, who has studied the effects of exercise in people with MS. As with many other medical conditions, multiple sclerosis tends to get worse faster when a person has comorbid issues such as heart disease, Type 2 diabetes, or hypertension. Exercise blocks or treats all of these comorbidities, which is the first pathway by which it can help people with MS, he says.
At the same time, he says that regular exercise can increase the blood’s levels of inflammation-blocking immune system chemicals while also lowering the blood’s levels of inflammation-promoting immune system chemicals. Runaway inflammation fuels the symptoms and progression of MS — as it does for many other diseases. And so exercise’s ability to reduce inflammation is a big deal, he says.
“There’s also emerging data that exercise affects the structure and function of the central nervous system itself,” says Motl. For people with MS, the immune system attacks and breaks down the myelin that surrounds and protects the nerves of the brain and spinal cord. “The disease gets worse for people with multiple sclerosis because they lose myelination around the nerves, and eventually they lose the nerves themselves,” he explains. “But we’ve shown that exercise can slow down that loss or in some cases even prevent that demyelination.”
How? Exercise involves and activates every organ of the body, including the brain. And similar to the way a muscle grows larger in response to strength training, the brain seems to experience growth in response to exercise. “The brain is an adaptive organ,” Motl says. By boosting the brain’s levels of growth-promoting chemicals and metabolic activity, “exercise is a stimulus that builds it up,” he says.
Exercise and the mind
According to the latest figures from the U.S. National Institute of Mental Health, about 1 in 14 Americans experienced an episode of major depression during the past year. The numbers are more dire among young adults and adolescents; roughly 1 in 8 Americans aged 12 to 25 experienced a depressive episode last year, and that’s true of fully 1 in 5 adolescent women.
Depression is categorized as a disease of the mind, but it has grave implications for the health of the body. Writing in the journal Circulation, doctors at the American Heart Association lay out the evidence that young people diagnosed with depression are at elevated risk for early-onset heart disease and arterial disease. Recent studies have also found that the risk of early death is much higher among people with mental health disorders, including depression, compared with the general population even after excluding suicide. Depression is associated with a dysregulation of the immune and nervous systems, and it disrupts metabolic and hormone activity — all of which may promote the development of diseases, argues a 2018 review in Frontiers in Psychiatry.
Most people with depression are treated with a combination of drugs and psychotherapy. But regular exercise may prove to be a more potent aid than either of them. “Physical activity improves the symptoms of depression through mechanisms both above and below the neck,” says Martino Belvederi Murri, first author of the Frontiers review and an assistant professor in the Institute of Psychiatry at the University of Ferrara in Italy.
Murri says that regular exercise helps regulate the brain and blood’s levels of neurotransmitters like dopamine and serotonin in ways that appear to improve and stabilize mood and also bolsters thinking. “[Exercise] also tends to reduce the neurotoxic effects of inflammation in the brain while promoting the growth of newborn neurons and the connections between existing ones,” he says. “This explains why the brains of people who are physically active tend to be functionally and structurally more healthy than those of people who are sedentary.”
It may be helpful to think of a sedentary brain and body as akin to a plant locked in a dark closet. No matter how well the plant is fed or watered, it will die without sunlight. The same seems to be true of a human body denied regular physical activity.
There’s research linking exercise to improvements among people with anxiety disorders, bipolar disorder, and other mood disorders. There’s also abundant evidence that exercise can help manage chronic pain conditions such as arthritis. While some of this evidence is deemed weak by modern scientific standards, that weakness is mostly due to a lack of well-funded clinical exercise trials. But all that’s about to change, thanks in large part to the launch of the largest-ever government-funded study on the effects of exercise on the human body.
Looking to the future of exercise as medicine
While more and more doctors today recognize the therapeutic power of exercise, experts say there’s still a ways to go. “In general, I don’t think that the majority of the medical community believes that exercise can be as effective as whatever drugs they might prescribe to treat or prevent a certain condition,” says Kohrt, the University of Colorado professor.
Part of the hesitancy, she says, is that the biochemical mechanisms undergirding exercise’s therapeutic benefits are, at this point, not well understood. But she and a large, nationwide group of researchers are working to change that.
In June 2015, the NIH announced it was launching a $170 million, multifaceted research effort to better understand the effects of exercise on the human body. Known as the Molecular Transducers of Physical Activity Consortium, or MoTrPAC (pronounced “motor-pack”), the trial will include thousands of people and many more animal and lab specimens. Its aim is to develop a detailed map of the molecular, genetic, epigenetic, and other changes that take place in the body during and after exercise. The trial is currently in the process of enrolling approximately 2,000 adults along with a smaller group of kids.