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Amateur boxing linked to brain cell injury

September 12, 2006

A study of 14 Swedish amateur boxers suggests that they have higher levels of certain chemicals in their cerebrospinal fluid in the days following a bout, indicating injuries to neurons and other cells important to brain function, according to a report in the September issue of Archives of Neurology, one of the JAMA/Archives journals.

About 20 percent of professional boxers develop chronic traumatic brain injury, according to background information in the article. Some studies have suggested that amateur boxers also damage their nervous systems, but because their shorter bouts allow fewer blows to the head and because they must wear safety equipment, the effects tend to be less severe. These studies have been based on assessment of thinking, learning, memory and other brain functions long after boxing, rather than an immediate test performed soon after a fight.

Henrik Zetterberg, M.D., Ph.D., The Sahlgrenska Academy at Göteborg University, Göteborg, Sweden, and colleagues obtained spinal fluids (via spinal tap) from 14 amateur boxers (11 men and three women, average age 22 years) seven to 10 days after a bout and again three months later, after a rest from boxing. At the first assessment, the boxers reported how many hits to the head they received during the match and underwent physical and neurologic examinations; none showed signs of brain injury. The researchers also tested the cerebrospinal fluids of 10 healthy men who were not boxers as controls. Levels of several chemicals that indicate damage to brain cells (neurons) and their axons, the thread-like extensions of the cell that reach toward other brain cells to transmit electrical impulses, were measured.

Seven to 10 days after a boxing match, the group of boxers had higher average levels of chemicals known as neurofilament light protein and total tau than they did three months later. "The cerebrospinal fluid levels of these proteins increase in disorders with neuronal and axonal degeneration and damage, and the increase is known to correlate with the size of the brain lesion," the authors write. "When applied to the results of this study, the increases in neurofilament protein and total tau probably reflect damage to neuronal axons from hits to the head during a bout." They also had elevated levels of glial fibrillary acidic protein, which indicates damage to the astroglia, specialized cells that surround neurons to insulate and support them. An increase in this chemical was also recently found in patients who experienced severe brain injury, and the levels were linked to the patient's clinical outcome. Levels of all three chemicals were significantly higher in the seven boxers who had sustained more than 15 hits to the head or experienced grogginess during or after a bout, compared with those who had 15 or fewer hits to the head and no grogginess.

Compared with the non-boxers, immediately after a bout the boxers had higher levels of neurofilament light protein and glial fibrillary acidic protein. Three months later, the boxers still had higher levels of neurofilament light protein than the control subjects.

"Amateur boxing is associated with acute neuronal and astroglial injury," the authors conclude. "If verified in longitudinal studies with extensive follow-up regarding the clinical outcome, analyses of cerebrospinal fluid may provide a scientific basis for medical counseling of athletes after boxing or head injury."

JAMA and Archives Journals