If You Overdo It With Sport, Your Immune System Suffers

woman running

Exercise is good and well, but as with everything in life, the same applies here: Those who overdo it may suffer harm. Numerous studies have now found an apparent correlation between an active lifestyle and a healthier immune system. There is widespread consensus that regular, not overly intense, exercise strengthens the body’s defenses.

However, there is less agreement on the potential consequences of excessive exertion. Some studies point to a generally increased prevalence of infections in high-performance athletes, leading to correspondingly high rates of illness-related absences. It has been inferred that exceptionally demanding physical stress can weaken the immune system and increase the risk of infection. In sports medicine, this phenomenon is known as the Open-Window Effect.

Wildfire Fighter

Wildfire Fighter
Firefighters who deal with forest fires are often exposed to extreme stress. This could also have an effect on the immune system.

Another, equally demanding professional group is now providing new insights into possible connections between the immune system and extreme exertion: a team led by Ernesto Nakayasu from the Pacific Northwest National Laboratory in Richland, Washington, has examined what happens to the immune system immediately after a physically demanding activity in firefighters.

Eleven firefighters, specializing in combating wildfires, volunteered for this study published in the journal Military Medical Research, agreeing to donate blood plasma, urine, and saliva. Samples were collected from the participants before and after the 45-minute, demanding exercise, during which they had to carry around 20 kilograms of equipment over hilly terrain.

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 stage,” said Kristin Burnum-Johnson, a bioanalytical chemist at PNNL. “Perhaps we can reduce the risk of strenuous exercise for first responders, athletes, and members of the military.

Improved Gas Exchange

After analyzing the samples post-exercise, the team indeed found evidence of how intense physical activities impact the immune system. Initially, Nakayasu and colleagues observed expected values for processes aiding the body in meeting the increased demand for fluid, energy, and oxygen. However, alongside this, the researchers noted a decrease in molecules involved in inflammation. This was accompanied by an increase in Opiorphin, a substance contributing to the dilation of peripheral blood vessels.

The ultimate implications of these changes for the short-term function of the immune system are not entirely clear, but the researchers have a hypothesis: “[Opiorphin] may increase blood flow to muscles during the exercise regimen to improve the delivery of oxygen and nutrients,” notes the team. “We postulate that the decrease in inflammatory molecules we observed in the saliva after exercise might represent an adaptive mechanism to improve gas exchange in response to higher cellular oxygen demand.”

Altered Oral Biome

The microbiome in the mouths of firefighters also changed, likely due to an increase in antimicrobial peptides. The research group speculates that this process is a compensatory mechanism for immune suppression following intense exercise. However, the increase in antimicrobial peptides did not have any effect on stopping the growth of E. coli. This suggests that these peptides are not very good at protecting against host infections in the mouth.

Not all colleagues agree with such conclusions; some interpret the results as an elevated state of immune surveillance. Nakayasu and his team acknowledge that their small sample size limits broad conclusions. In conjunction with previous study findings, the research suggests a correlation between strenuous physical activity and an increased incidence of respiratory infections.