Objectives: To investigate the association of concussion with cognitive ability (CA) and educational level (EL).
Design: Epidemiological-cross-linkage of national computer registers.
Setting: Denmark.
Participants: 130 420 young men appearing before the Danish draft board during the period 2006-2010.
Primary and secondary outcome measures: CA test scores, EL and occurrence of concussion during the period 2004-2009, treated either in an A&E unit or upon admission to a hospital ward.
Results: The 3067 men who had suffered a concussion had lower CAs (mean=96.5, SD=15, 95% CI 95.0 to 97.0) than the total cohort and they were lower for 1452 who were admitted to a hospital ward (mean CA=95.8, SD=15, 95% CI 95.1 to 96.6) than for 1615 who were treated only at an A&E unit (mean CA=97.1, SD=15, 95% CI 96.3 to 98.0). Multiple logistic regressions revealed that the effects for EL were stronger than those for CA. Among 127 353 men not sustaining a concussion, 48% attended a 'gymnasium' (sixth-form college), among men treated for a concussion at an A&E unit, this falls to 36% and among men hospitalised for a concussion to 30%. Transfer to a gymnasium, if it happens, almost invariably does so before the 18th birthday. Among 701 men suffering a concussion and admitted to a hospital department after this date, only 26% (n=182) were previously transferred to a gymnasium. Among the 804 men treated at an A&E unit after their 18th birthday, 33% (n=265) had done so. These two percentages are significantly below the corresponding non-concussed population (48%).
Conclusions: Taken together, the results suggest that lower CA and, in particular, lower EL are risk factors for sustaining a concussion, the risk increasing with the severity of the injury.