Worrying too much about stressful events can trigger inflammation, according to a new study.
Researchers found dwelling on negative events can increase levels of inflammation in the body.
They discovered that when study participants were asked to ruminate on a stressful incident, their levels of C-reactive protein, a marker of tissue inflammation, rose.
The study is the first time to directly measure this effect in the body.
Study lead author Peggy Zoccola, an assistant professor of psychology at Ohio University in the United States, said: 'Researchers have asked people to report their tendency to ruminate, and then looked to see if it connected to physiological issues. It's been correlational for the most part.'
The research team recruited 34 healthy young women to participate in the project.
Each woman was asked to give a speech about her candidacy for a job to two interviewers in white laboratory coats, who listened with 'stone-faced' expressions.
Half of the group was asked to contemplate their performance in the public speaking task, while the other half was asked to think about neutral images and activities, such as sailing ships or grocery store trips.
The researchers drew blood samples that showed that the levels of C-reactive protein were significantly higher in the subjects who were asked to dwell on the speech.
For these participants, the levels of the inflammatory marker continued to rise for at least one hour after the speech.
During the same time period, the marker returned to starting levels in the subjects who had been asked to focus on other thoughts.
The C-reactive protein is primarily produced by the liver as part of the immune system's initial inflammatory response. It rises in response to traumas, injuries or infections in the body.
C-reactive protein is widely used as a clinical marker to determine if a patient has an infection, but also if he or she may be at risk for disease later in life.
Doctor Zoccola said: 'More and more, chronic inflammation is being associated with various disorders and conditions.
'The immune system plays an important role in various cardiovascular disorders such as heart disease, as well as cancer, dementia and autoimmune diseases.'