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Review
. 2012 May;95(5):1079-88.
doi: 10.3945/ajcn.111.027995. Epub 2012 Apr 4.

Effects of Vitamin C Supplementation on Blood Pressure: A Meta-Analysis of Randomized Controlled Trials

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Free PMC article
Review

Effects of Vitamin C Supplementation on Blood Pressure: A Meta-Analysis of Randomized Controlled Trials

Stephen P Juraschek et al. Am J Clin Nutr. .
Free PMC article

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.

Design: 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.

Figures

FIGURE 1.
FIGURE 1.
Flow diagram of the trial selection process. Medline (www.pubmed.org); EMBASE (http://www.embase.com/home); Central (http://onlinelibrary.wiley.com/o/cochrane/cochrane_clcentral_articles_fs.html). BP, blood pressure; ESRD, end-stage renal disease.
FIGURE 2.
FIGURE 2.
Net changes in systolic BP (A) and diastolic BP (B) in randomized trials of vitamin C supplementation. The area of each square is proportional to the study weight in the analysis. Horizontal lines represent 95% CIs. Diamonds represent pooled estimates. Galley et al (36) included 2 distinct trial populations: hypertensives (H) and normotensives (N). Keith included 2 distinct trial populations: smoking (S) and nonsmoking (NS). BP, blood pressure; T/C, treatment group/control group.

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