title: Removing confounders from the relationship between mortality risk and systolic blood pressure at low and moderately increased systolic blood pressure.
abstract: OBJECTIVE
  To assess the relationship between mortality risk and systolic blood pressure (SBP) at low and moderately increased SBP (less than the 70th percentile) before and after correcting for the regression-dilution bias and J-curve effects.
  
  
  METHODS
  Cohort study.
  
  
  METHODS
  The First National Health and Nutrition Examination Survey Epidemiologic Follow-Up Study.
  
  
  METHODS
  The 6839 individuals who participated in the 1982-1984 survey for whom there were no missing data (age range 34-87 years).
  
  
  METHODS
  Cardiovascular disease mortality (n = 678) during a 9-year follow-up.
  
  
  METHODS
  Corrections were made for the regression-dilution bias by using average SBP during the decade before baseline as the mortality predictor, and for J-curve effects by excluding individuals who exhibited high age-stratified mortality rates and a decrease in SBP. Cox's regression was used to analyse the follow-up relationship between mortality risk and SBP.
  
  
  RESULTS
  The corrected relative cardiovascular disease mortality risk was 1.23 (95% confidence interval (CI), 1.16 to 1.31) for a 10 mmHg increase in SBP. The relationship was monotonically positive starting at the lowest SBP category in the analysis (< 115 mmHg), and robustly so above about the 32nd percentile (120 mmHg). The equivalent uncorrected result was 1.08 (95% CI, 1.05 to 1.13), and the relationship was J-shaped and became positive above about the 68th percentile (135 mmHg). Below the 70th percentile of SBP, individuals in the corrected analysis were 89% of all individuals.
  
  
  CONCLUSIONS
  These two corrections transformed the relationship between mortality risk and SBP at low and moderately increased SBP from no association to a robustly positive association starting at 120 mmHg, for the majority of individuals.
authors.affiliation: Department of Health and Nutrition Sciences, Brooklyn College of the City University of New York, 2900 Bedford Avenue, Brooklyn, NY 11210, USA. jamesg@brooklyn.cuny.edu
authors.forename: James A
authors.initials: JA
authors.lastname: Greenberg
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002318:Cardiovascular Diseases / Q000401:mortality*; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D007022:Hypotension / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D018570:Risk Assessment; D013599:Systole