Dwelling on negative events raises levels of harmful inflammation within the body, a study finds. And research is pointing to chronic inflammation as a source of ailments such as coronary artery disease, diabetes, cancer, and possibly Alzheimer’s disease as well.

Stress is known to release hormones that can fuel inflammation, but a study from researchers at Ohio University is the first to directly measure the impact of the form of stress that comes from dwelling on negative thoughts and the reaction it has on C-reactive protein, a marker for inflammation.

For the study, researchers recruited 34 healthy young women and asked each to give a speech about her candidacy for a job to two interviewers in white laboratory coats.

Half of the group was asked to dwell on 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 a trip to the store.

The researchers then drew blood samples, which showed levels of C-reactive protein were significantly higher in the subjects who were asked to dwell on the speech. Their level of inflammatory marker continued to rise for at least one hour afterward.

During the same time period, the marker returned to initial levels in the subjects who had been asked to focus on other thoughts.

This study demonstrated that negative thinking, in this case thinking about a task that may or may not have gone well, can lead to higher levels of unhealthy inflammation within the body.