Brain inflammation may be a marker for clinical depression, suggests a small study by Canadian researchers.

“This finding provides the most compelling evidence to date of brain inflammation during a major depressive episode,” senior author Dr. Jeffrey Meyer of the Campbell Family Mental Health Research Institute at the Centre for Addiction and Mental Health, in Toronto, said in a news release. “Previous studies have looked at markers of inflammation in blood, but this is the first definitive evidence found in the brain.”

Meyer and his team took brain scans on 20 patients with clinical depression who were otherwise healthy, and they compared them to the brain scans of 20 healthy people. The positron emission tomography (PET) scans showed that the depressed patients had a 30 percent increase in brain inflammation, compared to the control group.

“This discovery has important implications for developing new treatments for a significant group of people who suffer from depression,” Meyer said. “It provides a potential new target to either reverse the brain inflammation or shift to a more positive repair role, with the idea that it would alleviate symptoms.”

According to the news release, a growing body of evidence suggests that inflammation is linked to depressive symptoms such as low mood, loss of appetite and inability to sleep.

The Centers for Disease Control and Prevention (CDC) estimates that 1 in 10 U.S. adults has clinical depression.

Over half of people with the condition do not respond to treatment, Meyer said, and current treatments do not target inflammation.

“Depression is a complex illness and we know that it takes more than one biological change to tip someone into an episode,” Meyer said in the news release. “But we now believe that inflammation in the brain is one of these changes and that’s an important step forward.”  

The study was published Wednesday in the journal JAMA Psychiatry.