New Study Shows How "Vigorous Exercise" Can Make You Sick

Exercise does wonders for the mind, body, and soul. Getting active can improve your muscle strength, boost your endurance, and help lower your risk of developing chronic diseases such as heart disease and obesity. Research has also linked working out to reduced symptoms of anxiety and depression, according to The Journal of Clinical Psychiatry. But is there such a thing as getting too much exercise? Now that a new study has come to light, scientists say fitness fanatics may want to scale back on their gym routine.

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A study published in the journal Military Medical Research claims that "vigorous exercise" can actually stifle your immune system—and consequently, increase your likelihood of catching a virus or the common cold.

Kind of shocking, right? Not only did P.E. class teach us the exact opposite, but we've been told by many health organizations that exercise can be a natural immunity booster. For instance, the Gundersen Health System says immune cells live up to three hours post-workout, which allows them to "identify unwanted intruders and keep you from getting sick."

However, a group of researchers at the Pacific Northwest National Laboratory (PNNL) have debunked this theory. PNNL biomedical scientist Ernesto Nakayasu and his team analyzed over 4,700 post-workout fluid molecules and concluded that excessive exercise actually weakens the body's internal defense against harmful germs and bacteria.

"People who are very fit might be more prone to viral respiratory infection immediately after vigorous exercise. Having less inflammatory activity to fight off an infection could be one cause," explained Nakayasu in a press release.

Less inflammation can improve one's breathing, but it can also make the body more susceptible to viral respiratory infections. This is particularly concerning for professional athletes, whose livelihood directly correlates to their health, in addition to fitness trainers, emergency workers (firefighters and police), and the military, Nakayasu noted.

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For the study, researchers put 11 firefighters through 45 minutes of intense exercise before testing their blood plasma, urine, and saliva for changes.

"We wanted to take an in-depth look at what's happening in the body and see if we're able to detect danger from exhaustion in its earliest stages," explained PNNL bioanalytical chemist Kristin Burnum-Johnson.

The saliva results revealed a "decrease in signaling molecules important for inflammation and for fighting off viral infections," per the release. "However, this increase in antimicrobial peptides had no effect on inhibiting E. coli growth, suggesting a limited capacity of antimicrobial peptides within the oral cavity to protect against host infections," the researchers specified in their paper.

On a molecular level, "the differences before and after exercise underscored the body's efforts at tissue damage and repair, maintenance of fluid balance, efforts to keep up with increased energy and oxygen demand, and the body's attempts to repair and regenerate its proteins and other important substances," as explained in the release.

A 2020 study yielded similar results: Researchers found that "infection burden" is high among professional athletes and that "arduous exercise can suppress immunity and increase infection risk" among those who vigorously workout.

As for the current study, Nakaysu said, "There is evidence supporting a relationship between physical demands and a higher incidence of respiratory infections."

Best Life offers the most up-to-date information from top experts, new research, and health agencies, but our content is not meant to be a substitute for professional guidance. If you have health questions or concerns, always consult your healthcare provider directly.