The Association between Infections and General Cognitive Ability in Young Men – A Nationwide Study

Abstract

BackgroundInfections and activated immune responses can affect the brain through several pathways that might also affect cognition. However, no large-scale study has previously investigated the effect of infections on the general cognitive ability in the general population.MethodsDanish nationwide registers were linked to establish a cohort of all 161,696 male conscripts during the years 2006–2012 who were tested for cognitive ability, which was based on logical, verbal, numerical and spatial reasoning at a mean age of 19.4 years. Test scores were converted to a mean of 100.00 and with a standard deviation (SD) of 15. Data were analyzed as a cohort study with severe infections requiring hospitalization as exposure using linear regression.ResultsAdjusted effect sizes were calculated with non-exposure to severe infections as reference, ranging from 0.12 SD to 0.63 SD on general cognitive ability. A prior infection was associated with significantly lower cognitive ability by a mean of 1.76 (95%CI: -1.92 to -1.61; corresponding to 0.12 SD). The cognitive ability was affected the most by the temporal proximity of the last infection (P<0.001) and by the severity of infection measured by days of admission (P<0.001). The number of infections were associated with decreased cognitive ability in a dose-response relationship, and highest mean differences were found for ≥10 hospital contacts for infections (Mean: -5.54; 95%CI: -7.20 to -3.89; corresponding to 0.37 SD), and for ≥5 different types of infections (Mean: -9.44; 95%CI: -13.2 to -5.69; corresponding to 0.63 SD). Hospital contacts with infections had occurred in 35% of the individuals prior to conscription.ConclusionsIndependent of a wide range of possible confounders, significant associations between infections and cognitive ability were observed. Infections or related immune responses might directly affect the cognitive ability; however, associated heritable and environmental factors might also account for the lowered cognitive ability.

Integrative Analysis of Disease Signatures Shows Inflammation Disrupts Juvenile Experience-Dependent Cortical Plasticity

“…In fact, childhood infections and inflammation are associated with subsequent diagnoses of autism, depression, and schizophrenia as well as declines in cognitive capacity (Dalman et al, 2008; Atladóttir et al, 2010; Khandaker et al, 2014; Benros et al, 2015). The elevated incidence rate of infections during childhood neurodevelopment (relative to older ages) and the association of childhood infection with subsequent neurodevelopmental disorder may indicate a partial explanation for the observed onset of psychiatric disorders in childhood and adolescence (Lee et al, 2014).…”

A large population-based investigation into the genetics of susceptibility to gastrointestinal infections and the link between gastrointestinal infections and mental illness

“…All infection cases requiring hospital contact were identified in the Danish National Hospital Registry. All hospital contacts for infections were included with ICD-8 and ICD-10 codes listed in Supplementary Table S1, as used in previous studies (Benros et al 2013(Benros et al , 2015(Benros et al , 2016Nudel et al 2019), and each person may have had a history of more than one infection. We omitted all diagnoses with the modification code "suspected" or "not found".…”

Association of Childhood Infection With IQ and Adult Nonaffective Psychosis in Swedish Men

“…Third, prenatal/childhood infections can alter neurodevelopment as measured by IQ, school grades, or neurologic soft signs. 14,[16][17][18][19] However, there are also 3 important questions regarding the association of childhood infections with IQ and risk of psychosis. First, is there a sensitive period in development during which exposure to a serious infection is more harmful?…”