Boxers and mixed martial arts fighters show markers of long-term brain injury in their blood in a study by researchers at the Cleveland Clinic. Two brain proteins, neurofilament light chain and tau, are biological markers of brain injury. The two proteins are components of nerve fibers that can be detected in the blood when the fibers are injured. The researchers took blood samples from 291 active professional fighters with an average age of 30, 44 retired fighters with an average age of 45 and 103 non-fighters with an average age of 30. When the blood samples were tested for levels of both proteins, active professional fighters were found to have 40 percent higher levels of both proteins compared to retired fighters or non-fighters. Researchers also found that the more a fighter sparred in the two weeks before the blood samples were taken, the higher the levels of neurofilament light chain in their blood. As for brain size, researchers found that for fighters who had increasing levels of tau over time, there was a 7 percent decline in the volume of their thalamus, a part of the brain that regulates sleep, consciousness, alertness, cognitive function and language. The thalamus also sends sensory and movement signals to other portions of the brain.