A bidirectional association between cognitive ability in young adulthood and epilepsy: a population-based cohort study.

Aim: To investigate the bidirectional association between cognitive ability in young adulthood and epilepsy. Methods: This cohort study included 1 159 076 men enrolled in the mandatory conscription board examination from the Danish Conscription Database (DCD; 658 465 men examined 1957-84), the Danish Defence Personnel Organization Database (DPOD; 216 509 men examined 1987-2005) and the Danish Conscription Registry (DCR; 284 102 men examined 2006-15). A supplementary analysis included 14 814 female volunteers. Cognitive ability was measured at conscription, and epilepsy was ascertained by physician diagnoses in the Danish National Patient Registries 1977-2016 [using International Classification of Diseases (ICD) codes: ICD-8-345; ICD-10-G40-G41]. Differences in cognitive ability in relation to epilepsy status at the time of conscription (age 19) were calculated using linear regression. The risk of epilepsy associated with cognitive ability was estimated using Cox regression models, split at age at follow-up (40 and 60 years) and adjusted for year of birth, cerebrovascular disease, traumatic brain injury and education. Results: In all, 5097 (1.0%) men from the DPOD and DCR were diagnosed with epilepsy before conscription, and they had about 0.25 standard deviation (SD) lower cognitive scores than men without epilepsy. The largest difference in cognition was seen for those with the largest number of hospital contacts. A total of 22 364 (1.9%) men developed epilepsy, and cognitive ability was inversely associated with the risk of epilepsy. With the end of follow-up at age 40 years, the adjusted hazard ratio (HR)per SD increase was 0.75 (95% confidence interval = 0.73-0.77). The association attenuated with increasing age at diagnosis. The findings were replicated in female conscripts. Conclusions: The cognitive impairment seen in adults with epilepsy seems to reflect combined effects of epileptic processes and lower premorbid cognitive ability.

Cognitive ability and risk of post-traumatic stress disorder after military deployment: an observational cohort study.

BACKGROUND: Studies of the association between pre-deployment cognitive ability and post-deployment post-traumatic stress disorder (PTSD) have shown mixed results. AIMS: To study the influence of pre-deployment cognitive ability on PTSD symptoms 6-8 months post-deployment in a large population while controlling for pre-deployment education and deployment-related variables. METHOD: Study linking prospective pre-deployment conscription board data with post-deployment self-reported data in 9695 Danish Army personnel deployed to different war zones in 1997-2013. The association between pre-deployment cognitive ability and post-deployment PTSD was investigated using repeated-measure logistic regression models. Two models with cognitive ability score as the main exposure variable were created (model 1 and model 2). Model 1 was only adjusted for pre-deployment variables, while model 2 was adjusted for both pre-deployment and deployment-related variables. RESULTS: When including only variables recorded pre-deployment (cognitive ability score and educational level) and gender (model 1), all variables predicted post-deployment PTSD. When deployment-related variables were added (model 2), this was no longer the case for cognitive ability score. However, when educational level was removed from the model adjusted for deployment-related variables, the association between cognitive ability and post-deployment PTSD became significant. CONCLUSIONS: Pre-deployment lower cognitive ability did not predict post-deployment PTSD independently of educational level after adjustment for deployment-related variables. DECLARATION OF INTEREST: None. COPYRIGHT AND USAGE: © The Royal College of Psychiatrists 2017. This is an open access article distributed under the terms of the Creative Commons Non-Commercial, No Derivatives (CC BY-NC-ND) license.

Cognitive ability in young adulthood and risk of dementia in a cohort of Danish men, brothers, and twins.

INTRODUCTION: We examined the association between cognitive ability in young adulthood and dementia in Danish men, brothers, and male twins. METHODS: In total, 666,986 men born between 1939 and 1959 were identified for dementia diagnosis in national registries from 1969 to 2016. The association between cognitive ability from draft board examination and dementia was examined using Cox regression. RESULTS: During a 44-year follow-up, 6416 (0.96%) men developed dementia, 1760 (0.26%) and 970 (0.15%) of which were classified as Alzheimer's and vascular dementia, respectively. Low cognitive ability was associated with increased risk of dementia (hazard ratio [HR]per SD decrease 1.33 [95% confidence interval {CI} = 1.30-1.35]) with the strongest associations for vascular dementia (HRper SD decrease 1.47 [95% CI = 1.31-1.56]) and a weaker for Alzheimer's disease (HRper SD decrease 1.07 [95% CI = 1.03-1.13]). The intrabrother and twin analyses (taking shared family factors into account) showed attenuated risk estimates but with wide CIs. DISCUSSION: Low early-life cognitive ability increases the risk of dementia before the age of 78 years. The association is partly explained by shared family factors.