title: Effects of vitamin C supplementation on blood pressure: a meta-analysis of randomized controlled trials.
abstract: BACKGROUND
  In observational studies, increased vitamin C intake, vitamin C supplementation, and higher blood concentrations of vitamin C are associated with lower blood pressure (BP). However, evidence for blood pressure-lowering effects of vitamin C in clinical trials is inconsistent.
  
  
  OBJECTIVE
  The objective was to conduct a systematic review and meta-analysis of clinical trials that examined the effects of vitamin C supplementation on BP.
  
  
  METHODS
  We searched Medline, EMBASE, and Central databases from 1966 to 2011. Prespecified inclusion criteria were as follows: 1) use of a randomized controlled trial design; 2) trial reported effects on systolic BP (SBP) or diastolic BP (DBP) or both; 3) trial used oral vitamin C and concurrent control groups; and 4) trial had a minimum duration of 2 wk. BP effects were pooled by random-effects models, with trials weighted by inverse variance.
  
  
  RESULTS
  Twenty-nine trials met eligibility criteria for the primary analysis. The median dose was 500 mg/d, the median duration was 8 wk, and trial sizes ranged from 10 to 120 participants. The pooled changes in SBP and DBP were -3.84 mm Hg (95% CI: -5.29, -2.38 mm Hg; P < 0.01) and -1.48 mm Hg (95% CI: -2.86, -0.10 mm Hg; P = 0.04), respectively. In trials in hypertensive participants, corresponding reductions in SBP and DBP were -4.85 mm Hg (P < 0.01) and -1.67 mm Hg (P = 0.17). After the inclusion of 9 trials with imputed BP effects, BP effects were attenuated but remained significant.
  
  
  CONCLUSIONS
  In short-term trials, vitamin C supplementation reduced SBP and DBP. Long-term trials on the effects of vitamin C supplementation on BP and clinical events are needed.
authors.affiliation: Johns Hopkins School of Medicine, Johns Hopkins Bloomberg School of Public Health, and Welch Center for Prevention, Epidemiology, and Clinical Research, Johns Hopkins Medical Institutions, Baltimore, MD 21205, USA.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Juraschek
authors.forename: Eliseo
authors.initials: E
authors.lastname: Guallar
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Appel
authors.forename: Edgar R
authors.initials: ER
authors.lastname: Miller
mesh_terms: D001205:Ascorbic Acid / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects*; D019587:Dietary Supplements; D006801:Humans; D006973:Hypertension; D016032:Randomized Controlled Trials as Topic; D014815:Vitamins / Q000494:pharmacology*
chemical_list: D014815:Vitamins; D001205:Ascorbic Acid