The problem of head injuries in sports like ice hockey and American football has increased markedly in the last ten years. Thus far so-called retrospective (“looking back”) studies have examined individuals who have already had a mild head injury, finding impairments of the brain’s cognitive function, that is, its ability to interpret and comprehend the surrounding world through memory and learning, for instance, several years after the injury.
The Umeå scientists’ study is prospective (“looking forward”), meaning they have followed a large group of individuals over time and noted the injuries that have been incurred and their consequences. The study covers more than 300,000 young men who took part in the cognitive tests for entering national military service in 1989 and 1994. Among them, 4,713 had incurred a mild traumatic head injury prior to this test, while 11,217 suffered such a head injury after the testing.
The study showed that those individuals who had experienced a mild traumatic brain injury before the test of their cognitive function when signing up for service had 5-percent lower test scores than those who never incurred such a brain injury. On the other hand, the more than 11,000 young men who, according to medical statistics, had had a mild traumatic brain injury after the test for military service had 6-percent lower scores.
Furthermore, the 795 men who had suffered at least two mild traumatic brain injuries after the tests for military service had scores that were fully 15 percent lower. Moreover, a number of sets of twins were identified where only one twin had had a mild traumatic brain injury before the cognitive tests for military service. Both twins turned out to have lower test scores when entering military service.
Independent risk factors for a mild traumatic brain injury in the entire group under study were, besides low cognitive function, also hospital-treated alcohol poisoning, low level of education, and earlier brain injuries.
The results show that low cognitive function is probably a risk factor for, and not a long term result of, mild traumatic brain injury. The lower test scores in sets of twins when one of the twins had incurred a mild traumatic brain injury before the cognitive tests indicate that there are hereditary causes of the lower cognitive capacity. The research team has previously shown that low cognitive function is also a risk factor for severe traumatic head injuries in young men.
In an editorial response to the article authored by researcher at Umeå University, two researchers at Cambridge University in the UK proclaim that the study provides unique insights into patterns of disease in mild traumatic brain injury, and therefore, the results are important for several reasons. However, they point out that further studies are needed to confirm the findings and to increase awareness of this type of problem.
A Nordström, BB Edin, S Lindström, P Nordström: Cognitive function and other risk factors for mild traumatic brain injury in young men: nationwide cohort study. British Medical Journal, 21 February 2013 doi=10.1136/bmj.f723