For some people, violent behavior and anger may be linked with inflammation in their bodies, a new study finds.
The researchers measured markers of inflammation in the blood of 70 people diagnosed with intermittent explosive disorder (IED), a condition that involves repeated episodes of impulsive aggression and temper tantrums, as seen in road rage, domestic abuse and throwing or breaking objects.
The study also included 61 people diagnosed with psychiatric disorders not involving aggression, and 67 participants with no psychiatric disorder, who served as controls.
The results showed a direct relationship between levels of two markers of inflammation and impulsivity and aggression in people with IED, but not in control participants. The results held after controlling for lifestyle factors and other differences between groups of participants, according to the study published today (Dec. 18) in the journal JAMA Psychiatry.
How the link may work remains unclear, the researchers said.
"We don't know yet if the inflammation triggers aggression, or aggressive feelings set off inflammation, but it's a powerful indication that the two are biologically connected, and a damaging combination," said study researcher Dr. Emil Coccaro, a professor of psychiatry at the University of Chicago.
The finding doesn't mean that taking anti-inflammatory medication such as aspirin would calm an angry person, Coccaro told LiveScience. But it does open a new direction for future studies, which could focus on whether reducing inflammation could eventually reduce aggression. [10 Things You Didn't Know About the Brain]
People with IED overreact to stressful situations with uncontrollable anger and rage. The condition affects people's professional and social lives, and may put them at higher risks for other mental problems, such as depression, anxiety and alcohol or drug abuse, the researchers said. People with IED also face increased risk for medical problems, such as heart disease, stroke and diabetes, they said.
Treatment for IED includes mood stabilizers and psychotherapy, but they are not always successful for all patients, Coccaro said.
In the study, the researchers focused on two markers of inflammation, called C-reactive protein (CRP) and interleukin-6 (IL-6). CRP is produced by the liver in response to an infection or injury, whereas IL6 is secreted by white blood cells to stimulate immune responses. Blood levels of both CRP and IL-6 rise when the body's inflammatory response is activated.
The study also found that both CRP and IL-6 levels were higher, on average, in people with IED, compared with other participants, and that both markers were particularly elevated in people who had more aggressive behaviors in the past.
Animal studies have shown that introducing similar inflammatory proteins into the brains of cats and mice increase their aggressive behavior. It is possible that in humans, too, some of the elevated proteins in the blood find their way to the brain and affect brain regions that control aggressive behavior, the researchers said.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.