Researchers say that thinking about past mistakes could increase inflammation, which supports an earlier hypothesis that depression may be linked to chronic inflammation.

Those who’ve stayed awake at night tossing and turning and dwelling on past mistakes know it can make a good night’s sleep difficult, but research shows that it may do more than just make you drowsy the next morning.

Researchers at Ohio State University say that thinking about negative experiences actually increases inflammation in the body.

Inflammation is the immune system’s response to outside dangers, and demonstrates that the body is working to repair any damage, from an infection to a laceration. However, chronic inflammation has been linked to numerous health problems, including depression, heart disease, cancer, and diabetes.

Coupled with other recent findings about the influence of inflammation on mood, scientists are closer than ever to understanding the long-term effects of common mental health problems.

Ohio researchers recruited 34 healthy women to give a speech as part of a job interview to two stern-faced interviewers in white lab coats. After, half were asked to think about their performance, while the other half thought about neutral acts like going to the grocery store.

Researchers found that the women who dwelled on the interview had significantly higher levels of C-reactive protein in their blood, a marker of inflammation produced by the liver. C-reactive protein levels are used to determine whether a person has an infection, but can also help predict if an individual is likely to have chronic health problems later in life.

“More and more, chronic inflammation is being associated with various disorders and conditions,” lead study author Peggy Zoccola, an assistant professor of psychology at Ohio State, said in a press release. “The immune system plays an important role in various cardiovascular disorders, such as heart disease, as well as cancer, dementia, and autoimmune diseases.”

The fact that this study involved a small sample population, only included women, and has yet to be published in a peer-reviewed journal means that it should only be considered a preliminary finding.

It does, however, bolster research published earlier this year linking depression and elevated levels of C-reactive protein to an increased risk of depression and other types of psychological illness.

In January, Danish researchers reported that elevated levels of C-reactive protein may be associated with an increased risk of depression. They used data from the Copenhagen General Population study, and specifically information from 73,131 Danes ages 20 to 100.

The researchers hypothesized that depression could be an inflammatory disorder, but noted that more research is needed to reach a definitive conclusion.

A 2011 study published in the Journal of Neuroinflammation demonstrated that some people with chronic depression and suicidal tendencies also had high levels of quinolinic acid—another byproduct of inflammation—in their spinal fluid.

While it’s too early to say there is a cause-and-effect relationship between inflammation and depression, researchers are finding new avenues for research that could help us better understand mental health, as well as find new, more effective treatments for depression, bipolar disorder, and other mental illnesses.