Q: I’ve heard that high-intensity or prolonged exercise is bad for my cortisol levels. Is this true?
In recent years, wellness influencers have become fixated on cortisol, blaming the stress hormone for various symptoms, including a puffy face, excess belly fat, burnout and fatigue. Some have offered supposed solutions for lowering your cortisol.
Many also suggest that high-intensity or prolonged aerobic exercise puts too much stress on your body and causes your cortisol level to spike in an unhealthy way. Some say heavy lifting has a similar effect. These influencers advise ditching strenuous workouts for more gentle or low-intensity forms of movement, like walking, yoga and Pilates.
But scientists say this is a misunderstanding of cortisol’s role in the body. And a surge in cortisol, they add, is not always bad, especially in response to exercise.
“Social media is using cortisol synonymously with the word ‘stress,’ and cortisol doesn’t always mean stress,” said Dr. Lena Fan, an endocrinologist and assistant professor at the Icahn School of Medicine at Mount Sinai.
We asked exercise and hormone experts to explain the science around exercise and cortisol.
Cortisol is essential to good health.
Cortisol’s main role is to help your body respond to stress: When you are under strain, your adrenal glands release the hormone to help set off the so-called fight-or-flight response. Cortisol helps increase blood flow to your muscles and gives you a burst of energy by spurring your body to convert fast-acting carbohydrates to fuel. All of these responses would be essential if, say, you were being chased and needed to run away as quickly as possible, Dr. Fan said.
Cortisol also helps your body fight off infection and inflammation, and helps regulate your heart rate, blood pressure, blood sugar and sleep cycle. Cortisol typically fluctuates throughout the day, rising when you wake up and dipping in the hours before bed to prepare your body for rest.
Cortisol disorders are rare.
While chronically high cortisol may seem common from conversations on social media, cortisol disorders are, in fact, rare, Dr. Fan said. Only about 1 percent of the population has cortisol levels above the normal range.
Even if you have chronic stress or anxiety, your cortisol levels are likely to increase but stay within the normal range, she said.
There’s also an important nuance that tends to get lost on social media, said Anthony Hackney, a professor emeritus of exercise physiology at the University of North Carolina. When you are stressed, a “pantheon of hormones” are released along with cortisol, including adrenaline, he said. Over time, if this mix of hormones stays elevated because of chronic stress, you could develop high blood pressure and other cardiovascular issues.
But cortisol is rarely the sole cause of these issues, Dr. Hackney said, and avoiding high-intensity exercise isn’t typically the solution.
Strenuous exercise can lower cortisol over time.
The stress of exercise signals to your body that it should release cortisol. The more you exert yourself, the more cortisol is released. This is a good thing during a workout, Dr. Hackney said, because the hormone helps deliver more oxygen to your muscles.
Cortisol typically stays high for a few hours after exercise, but once you’ve recovered and refueled, it drops back down — often to a lower level than where it started. Over time, as your body adapts to strenuous exercise, your base line cortisol level may also decrease.
“It’s similar to building a muscle,” Dr. Fan said. “You’re training your body over time to be more resilient.”
Even during extremely strenuous exercise, your cortisol levels generally stay in the normal range, said Stuart Phillips, a professor of kinesiology at McMaster University in Ontario.
Proper fueling and recovery are key.
In order for strenuous exercise to lower stress and base line cortisol, you have to eat enough and build in time for recovery, said Dr. Marie Schaefer, a co-director of the women’s integrated sport, exercise and research center at the Cleveland Clinic.
If you do a hard workout but haven’t eaten enough fuel, including carbohydrates, it may feel more challenging and your cortisol will likely remain high for longer afterward, Dr. Schaefer said. Overtraining, or doing long, hard workouts without proper rest and recovery, she said, can negate some of the stress-lowering benefits of exercise.
Your recovery needs are likely to change depending on your sleep and stress levels, and your age, the experts said. If you don’t feel up for a strenuous workout on a given day, lower intensity workouts like yoga, Pilates, walking and tai chi can also lower stress by regulating your heart rate, breathing and more.
Finally, prioritize sleep, the experts said, to maximize your recovery and to help your body maintain normal cortisol levels.
Ultimately, “tune in, listen to your body a little bit, be gentle with yourself in times where you’re not feeling your best,” Dr. Phillips said. But don’t give up your HIIT workouts or long runs in the name of cortisol.
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