title: Methodological issues in cohort studies that relate sodium intake to cardiovascular disease outcomes: a science advisory from the American Heart Association.
abstract: BACKGROUND
  The results of cohort studies relating sodium (Na) intake to blood pressure-related cardiovascular disease (CVD) are inconsistent. To understand whether methodological issues account for the inconsistency, we reviewed the quality of these studies.
  
  
  RESULTS
  We reviewed cohort studies that examined the association between Na and CVD. We then identified methodological issues with greatest potential to alter the direction of association (reverse causality, systematic error in Na assessment), some potential to alter the direction of association (residual confounding, inadequate follow-up), and the potential to yield false null results (random error in Na assessment, insufficient power). We included 26 studies with 31 independent analyses. Of these, 13 found direct associations between Na and CVD, 8 found inverse associations, 2 found J-shaped associations, and 8 found null associations only. On average there were 3 to 4 methodological issues per study. Issues with greater potential to alter the direction of association were present in all but 1 of the 26 studies (systematic error, 22; reverse causality, 16). Issues with lesser potential to alter the direction of association were present in 18 studies, whereas those with potential to yield false null results were present in 23.
  
  
  CONCLUSIONS
  Methodological issues may account for the inconsistent findings in currently available observational studies relating Na to CVD. Until well-designed cohort studies in the general population are available, it remains appropriate to base Na guidelines on the robust body of evidence linking Na with elevated blood pressure and the few existing general population trials of the effects of Na reduction on CVD.
authors: Laura K
authors: LK
authors: Cobb
authors: Cheryl A M
authors: CA
authors: Anderson
authors: Paul
authors: P
authors: Elliott
authors: Frank B
authors: FB
authors: Hu
authors: Kiang
authors: K
authors: Liu
authors: James D
authors: JD
authors: Neaton
authors: Paul K
authors: PK
authors: Whelton
authors: Mark
authors: M
authors: Woodward
authors: Lawrence J
authors: LJ
authors: Appel
mesh_terms: D000572:American Heart Association; D002318:Cardiovascular Diseases / Q000453:epidemiology*; D015331:Cohort Studies; D006801:Humans; D015994:Incidence; D012307:Risk Factors; D012982:Sodium, Dietary / Q000009:adverse effects*; D014481:United States
chemical_list: D012982:Sodium, Dietary
keywords: AHA Scientific Statements; cardiovascular diseases; coronary diseases; diet; sodium; stroke