Background: There are few identified risk factors for traumatic brain injuries such as subdural hematoma (SDH). The aim of the present study was to investigate whether low cognitive performance in young adulthood is associated with SDH later in life. A second aim was to investigate whether this risk factor was associated with education and physical fitness.
Methods and findings: Word recollection, logical, visuospatial, and technical performances were tested at a mean age of 18.5 years in a prospective nation-wide cohort of 440,742 men. An estimate of global intelligence was calculated from these four tests. Associations between cognitive performance, education, physical fitness, and SDH during follow-up were explored using Cox regression analyses. During a median follow-up of 35 years, 863 SDHs were diagnosed in the cohort. Low global intelligence was associated with an increased risk of SDH during follow-up (hazard ratio [HR]: 1.33, per standard deviation decrease, 95% CI = 1.25-1.43). Similar results were obtained for the other measures of cognitive performance (HR: 1.24-1.33, p<0.001 for all). In contrast, a high education (HR: 0.27, comparing more than 2 years of high school and 8 years of elementary school, 95% CI = 0.19-0.39), and a high level of physical fitness (HR: 0.76, per standard deviation increase, 95% CI = 0.70-0.83), was associated with a decreased risk of suffering from a SDH.
Conclusions: The present findings suggest that reduced cognitive function in young adulthood is strongly associated with an increased risk of SDH later in life. In contrast, a higher level of education and a higher physical fitness were associated with a decreased risk of SDH.