Cognitive function and other risk factors for mild traumatic brain injury in young men: nationwide cohort study.

OBJECTIVE: To investigate cognitive function and other risk factors for mild traumatic brain injury in young men.

DESIGN: Nationwide prospective cohort study.

SETTING: Sweden.

PARTICIPANTS: 305 885 men conscripted for military service from 1989 to 1994.

MAIN OUTCOME MEASURE: mild traumatic brain injuries in relation to cognitive function and other potential risk factors assessed at conscription and follow-up.

RESULTS: Men with one mild traumatic brain injury within two years before (n=1988) or after cognitive testing (n=2214) had about 5.5% lower overall cognitive function scores than did men with no mild traumatic brain injury during follow up (P<0.001 for both). Moreover, men with at least two mild traumatic brain injuries after cognitive testing (n=795) had 15% lower overall cognitive function scores compared with those with no such injury (P<0.001). Independent strong risk factors (P<1×10(-10)) for at least one mild traumatic brain injury after cognitive testing (n=12 494 events) included low overall cognitive function, a previous mild traumatic brain injury, hospital admission for intoxications, and low education and socioeconomic status. In a sub-cohort of twin pairs in which one twin had a mild traumatic brain injury before cognitive testing (n=63), both twins had lower logical performance and technical performance compared with men in the total cohort with no mild traumatic brain injury (P<0.05 for all).

CONCLUSION: Low cognitive function, intoxications, and factors related to low socioeconomic status were strong independent risk factors for mild traumatic brain injuries in men. The low cognitive function in twin pairs discordant for mild traumatic brain injury suggests a genetic component to the low cognitive function associated with such injuries. The study included only men, so inferences to women should be made with caution.