People dealing with health issues are frequently told to avoid stress — and a new study could reveal why it’s so bad for us.

In work appearing in this week’s issue of the Proceedings of the National Academy of Sciences, researchers sought to determine whether the stress of personal conflicts and competitive sports would trigger the release of molecules known as cytokines, which are linked to inflammation.

Scientists enlisted 122 young adults to fill out diaries about their activities over eight days, focusing on their interactions with others and whether these were positive or negative. The participants were also given stress tests in the lab, with saliva samples taken before and after to measure biological markers for inflammation.

The researchers found that cytokine levels went up after “negative” interactions, usually arguments. But playing sports didn’t have the same effect, even though it’s competitive.

Study co-author Shelley Taylor, a professor of psychology at the University of California, Los Angeles, said the link between stress and molecules linked to inflammation matters. “If you aren’t wounded, there’s no place for them to go, and they’re circulating,” she said. “It’s not like they’ve gone to the site of a wound and engaged in anti-infection activity.”

In addition, low-grade inflammation in the body can contribute to the buildup of artery-blocking plaque and lead to disorders caused by an out-of-control immune system, such as asthma.

“Stress activates the immune system in preparation for fighting infection and healing wounds,” Dr. Andrew Miller, a professor of psychiatry and behavioral sciences at Emory University School of Medicine in Atlanta, told HealthDay.

“This is not a bad thing, especially in the context of a situation where a fight and wounding may ensue. However, if the immune system is constantly activated,” he continued, “this can contribute to a multitude of chronic health problems, including cardiovascular disease, diabetes, cancer and neuropsychiatric disorders.”

More From WFNT