title: School Achievement and Risk of Eating Disorders in a Swedish National Cohort.
abstract: OBJECTIVE
  High achievement in school has been associated with increased risk of eating disorders, including anorexia nervosa (AN) and bulimia nervosa (BN), but causality of these relationships is unclear. We sought to examine the association between school achievement and AN or BN in a national cohort and to determine the possible contribution of familial confounding using a co-relative design.
  
  
  METHODS
  This national cohort study involved 1,800,643 persons born in Sweden during 1972 to 1990 who were still living in Sweden at age 16 years and were followed up for AN and BN identified from inpatient and outpatient diagnoses through 2012. We used Cox regression to examine the association between school achievement and subsequent risk of AN or BN, and stratified Cox models to examine the gradient in this association across different strata of co-relative pairs (first cousins, half siblings, full siblings).
  
  
  RESULTS
  School achievement was positively associated with risk of AN among females and males (hazard ratio [HR] per additional 1 standard deviation, females: HR = 1.29; 95% CI = 1.25-1.33; males: HR = 1.29; 95% CI = 1.10-1.52), and risk of BN among females but not males (females: HR = 1.16; 95% CI = 1.11-1.20; males: HR = 1.05; 95% CI = 0.84-1.31). In co-relative analyses, as the degree of shared genetic and environmental factors increased (e.g., from first-cousin to full-sibling pairs), the association between school achievement and AN or BN substantially decreased.
  
  
  CONCLUSIONS
  In this large national cohort study, high achievement in school was associated with increased risk of AN and BN, but this appeared to be explained by unmeasured familial (genetic and environmental) factors.
authors.affiliation: Lund University, Center for Primary Health Care Research, Malmö, Sweden.
authors.forename: Jan
authors.initials: J
authors.lastname: Sundquist
authors.affiliation: Lund University, Center for Primary Health Care Research, Malmö, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Ohlsson
authors.affiliation: Stanford University, Stanford Prevention Research Center, Stanford, CA.
authors.forename: Marilyn A
authors.initials: MA
authors.lastname: Winkleby
authors.affiliation: Lund University, Center for Primary Health Care Research, Malmö, Sweden.
authors.forename: Kristina
authors.initials: K
authors.lastname: Sundquist
authors.affiliation: Stanford University. Electronic address: kccrump@stanford.edu.
authors.forename: Casey
authors.initials: C
authors.lastname: Crump
mesh_terms: D000293:Adolescent; D000328:Adult; D000856:Anorexia Nervosa / Q000453:epidemiology*; D052018:Bulimia Nervosa / Q000453:epidemiology*; D015331:Cohort Studies; D004522:Educational Status; D005190:Family / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D016016:Proportional Hazards Models; D012042:Registries; D012307:Risk Factors; D012574:Schools; D035781:Siblings / Q000523:psychology*; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
keywords: achievement; anorexia nervosa; bulimia nervosa; eating disorders; schools