title: Cognitive ability in Swedish conscripts and future risk of venous thromboembolism: A co-relative prospective national study.
abstract: OBJECTIVE
  Cognitive ability measured via an IQ-test (intelligence quotient) has been associated with cardiovascular (CVD) incidence. Whether cognitive ability is associated with risk of venous thromboembolism (VTE) is unknown. The present nationwide co-relative study aims to determine whether cognitive ability in male conscripts is a predictor of VTE.
  
  
  METHODS
  A Swedish cohort of male conscripts (n=940,964) born in 1954-1970 with no history of previous VTE were followed from enlistment (1972-1990) until 2010. Data on cognitive ability, using an IQ-test at conscription, were linked with national hospital register data to calculate future risk of VTE requiring in-patient care. Using the Swedish Multi-Generation Register, we identified all full-siblings, half-siblings and first-cousin pair discordant for IQ. This co-relative design allows for adjustment for unmeasured shared genetic or environmental factors.
  
  
  RESULTS
  A total of 5110 (0.54%) males were affected by VTE. IQ was associated with risk for VTE (hazard ratio=HR 0.87 95% confidence interval 0.84-0.89 per standard deviation [SD] increment). The association was highly time dependent with attenuation of effect over time and significant interaction between time and IQ. IQ was also associated with VTE in first-cousin pairs (HR=0.74, 0.69-0.79) but not when examining discordant half-sibling pairs (HR=0.94, 0.82-1.08), and only weakly in full-sibling pairs (HR=0.91, 0.84-0.98).
  
  
  CONCLUSIONS
  The present study suggests that familial-shared environmental factors linked to cognitive ability might be involved in the etiology of VTE. However, it is unlikely that IQ by itself causes VTE.
authors.affiliation: Center for Primary Health Care Research, Lund University/Region Skåne, Malmö, Sweden. Electronic address: bengt.zoller@med.lu.se.
authors.forename: Bengt
authors.initials: B
authors.lastname: Zöller
authors.affiliation: Center for Primary Health Care Research, Lund University/Region Skåne, Malmö, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Ohlsson
authors.affiliation: Center for Primary Health Care Research, Lund University/Region Skåne, Malmö, Sweden; Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, CA, United States.
authors.forename: Jan
authors.initials: J
authors.lastname: Sundquist
authors.affiliation: Center for Primary Health Care Research, Lund University/Region Skåne, Malmö, Sweden.
authors.forename: Kristina
authors.initials: K
authors.lastname: Sundquist
mesh_terms: D003071:Cognition; D005192:Family Health; D020022:Genetic Predisposition to Disease; D006801:Humans; D015994:Incidence; D007361:Intelligence Tests; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012042:Registries; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D054556:Venous Thromboembolism / Q000453:epidemiology*
keywords: Cognitive ability; Epidemiology; Family study; IQ; Pulmonary embolism; Thrombosis