MONDAY, Jan. 23 (HealthDay News) -- Shedding some light on why stress might be bad for you, a new study finds that parts of your immune system ramp up when you get into personal conflicts with others.

It's not clear how this effect of stress may make you sick, but the activated parts of the immune system -- which cause inflammation in the body -- have been linked to conditions such as diabetes and cancer.

"The message is that the flotsam and jetsam of life predict changes in your underlying biology in ways that cumulatively could have a bad effect on health," said study co-author Shelley Taylor, a professor of psychology at the University of California, Los Angeles. "What this tells me is that people should be investing in socially supportive relationships, and they should not court relationships that lead to a great deal of conflict."

It's well-known that stress causes several reactions in the body. "Stress activates the immune system in preparation for fighting infection and healing wounds," explained Dr. Andrew Miller, a professor of psychiatry and behavioral sciences at Emory University School of Medicine, in Atlanta. "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, this can contribute to a multitude of chronic health problems, including cardiovascular disease, diabetes, cancer and neuropsychiatric disorders."

In the new study, 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.

The researchers paid 122 young adults (53 men and 69 women) to take part in the study. The participants filled 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. Saliva samples were taken before and after those tests, 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. This may be because "we're really talking about people doing friendly games," Taylor said. "We're not looking at USC playing in the football finals."

It's possible that some kinds of competitions, like poker games, could trigger inflammation, she said.

Why does it matter if stress triggers molecules linked to inflammation? "If you aren't wounded, there's no place for them to go, and they're circulating," Taylor said. "It's not like they've gone to the site of a wound and engaged in anti-infection activity."

Low-grade inflammation in the body can contribute to the buildup of artery-blocking plaque and contribute to disorders linked to an out-of-control immune system, such as asthma, Taylor said.

So what does this all mean? The challenge, Emory's Miller said, is figuring out which came first -- stress or inflammation.

"Do aggressive, socially disadvantaged individuals exhibit more inflammation because they are constantly stressed?" he asked. "Or are they running their immune system hot because that is their fundamental nature, and the cytokines are driving their aggression because cytokines induce the brain to perceive the world as threatening?"

The study appears in this week's issue of the Proceedings of the National Academy of Sciences.

More information

For more about stress, visit the U.S. National Library of Medicine.