This article is from the In-Depth Report The Science of Concussion and Brain Injury

Head Injury May Cause Mental Illness

A single blow to the head may increase the risk of subsequently developing a disorder
biker face planting

Credit: KIRK MASTIN Aurora

The safety of football continues to be a heated topic for players and parents, with mixed evidence regarding the effect of head injuries on mental illness. Past studies on the connection have often been methodologically flawed or yielded ambiguous results. Now a paper in April in the American Journal of Psychiatry, the largest study yet to investigate the link, finds that even a single head injury indeed increases the risk of later mental illness, especially if the injury occurs during adolescence.

Using Danish medical registries, researchers led by physician Sonja Orlovska of the University of Copenhagen studied 113,906 people who had been hospitalized for head injuries over a 23-year period. They discovered that in addition to cognitive symptoms caused by structural damage to the brain (such as delirium), these people were subsequently more likely than the general population to develop several psychiatric illnesses. Risk increased by 65 percent for schizophrenia and 59 percent for depression. Risk was highest in the first year postinjury but remained significantly elevated throughout the next 15 years. After the team controlled for several potential confounders, such as accident proneness and a family history of psychiatric problems, they found the strongest injury-related predictor for later onset of schizophrenia, depression and bipolar disorder was a head trauma experienced between the ages of 11 and 15.

“Previous studies have shown that head injury induces inflammation in the brain, which causes several changes—for example, an increased permeability of the blood-brain barrier,” Orlovska says. Normally the barrier protects the brain from potentially harmful contents in the bloodstream, but injury-induced inflammation may allow these substances access to the brain. “For some individuals, this might initiate damaging processes in the brain,” she says.

Because the exact mechanisms that lead from head injury to mental illness are still unknown, it is not clear whether there are specific ways to reduce the risk of mental illness after such an injury. For now the best a patient can do is follow established postinjury guidelines, such as getting plenty of rest and avoiding physically and mentally demanding activities for a specified period depending on the severity of the injury. Early detection can help improve the prognosis for mental illness, so Orlovska also recommends seeing a doctor as soon as any symptoms appear.

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