Study Finds Potential Downside to Vigorous Exercise We Didn’t Know About

Bad news for any extreme exercise enthusiast. excessive exercise can suppress your immune system. At least, that’s what an analysis of more than 4,700 fluid molecules from firefighters shows after exercise.

This can be problematic for workers who consistently have physically demanding jobs that require intense fitness training, such as emergency workers and athletes.

“People who are very fit may be more prone to a viral respiratory infection immediately after vigorous exercise,” suggests Ernesto Nakayasu, a biomedical scientist at the Pacific Northwest National Laboratory (PNNL). “Having less inflammatory activity to fight infection may be one reason.”

Although there is strong evidence to suggest that moderate physical activity in healthy individuals can benefit the immune system in the long term, what happens to the immune system immediately after vigorous exercise is controversial.

There is little reliable evidence to support the claim that intense exercise increases the risk of opportunistic infections, although several previous studies have reported higher rates of upper respiratory tract infections in athletes compared to controls after strenuous activity. Whether these are correlations or causation is unknown.

So Nakayasu and colleagues tested the blood plasma, urine, and saliva of 11 firefighters before and after 45 minutes of intense exercise while carrying up to 20 kilograms (44 pounds) of gear over hilly terrain.

“We wanted to take a deep look at what’s going on in the body and see if we’re able to detect the risk of exhaustion in its early stages,” explains PNNL bioanalytical chemist Christine Burnum-Johnson. “Maybe we can reduce the risk of strenuous exercise for first responders, athletes and the military.”

There’s no doubt that exercise does wonders for our health, from boosting our mood to boosting our immune systems. But as in previous studies, the new study found possible signs of immune suppression in trained firefighters.

Amid the expected physical changes that help our bodies retain the increased fluids, energy, and oxygen that exercise requires, there was a decrease in molecules involved in inflammation. This was accompanied by the addition of opiorphin, a peripheral blood vessel dilator.

What these changes ultimately mean for the short-term function of the immune system is unclear, but the researchers have a few ideas.

“[Opiorphin] may increase blood flow to muscles during an exercise regimen to improve oxygen and nutrient delivery,” the team wrote in their paper.

“We hypothesize that the reduction in inflammatory molecules we observed in saliva after exercise may be an adaptive mechanism to improve gas exchange in response to higher cellular oxygen demand.”

There was also a change in the participants’ oral microbiome. Scientists hypothesize that this is due to an increase in antimicrobial peptides found after intensive firefighter activity, possibly compensating for immune suppression, although this conclusion is disputed.

“However, this increase in antimicrobial peptides had no effect on inhibition E. coli growth,” Nakayasu and colleagues elaborate, “suggesting a limited capacity of oral antimicrobial peptides to defend against host infections.”

That said, other scientists argue that some of the observed changes may not be an indication of immune suppression, but of a “heightened state of immune surveillance and immune regulation.”

Although the within-subject comparison reduced the effect of their small sample, firefighters have unique exposure to pollutants during fires, which may also alter their immune responses. What’s more, this study only looked at healthy and active men, the researchers caution, so further research among the wider community is needed to confirm their findings.

However, given previous studies, “there is evidence to support an association between physical demands and a higher incidence of respiratory infections,” Nakayasu and team conclude.

This research has been published Military medical research.