Effects of vitamin C supplementation on essential hypertension A systematic review and meta-analysis

Background: Vitamin C as a supplement to treat hypertension has been proposed. However, it remains controversial whether vitamin C can improve blood pressure in patients with primary hypertension. Objectives: To analyze the effect of vitamin C (VitC) supplementation on systolic (SBP) and diastolic (DBP) blood pressure in patients with essential hypertension. Methods: We searched the Chinese Knowledge Infrastructure, VIP Database for Chinese Technical Periodicals, WANFANG Data, Cochrane Library, National Library of Medicine's PubMed, EMBASE, and other databases until June 2019. Eight RCTs involving 614 participants were analyzed. SBP and DBP before and after VitC supplementation were compared between the intervention and control groups. The risk of bias of individual studies was assessed using the Cochrane Collaboration risk of bias tool. Two reviewers selected studies independently of each other. The Cochrane Collaboration Review Manager 5.3 was used to perform the meta-analysis. Results: There was a significant difference in the change of SBP (weighted mean difference [WMD] = -4.09; 95% confidence interval [CI] -5.56, -2.62; P < .001) and DBP (WMD = -2.30; 95% CI -4.27, -.331; P = .02) between the groups. Further, there was a significant difference in the SBP (WMD = -3.75, 95% CI -6.24, -1.26, P = .003) and DBP (WMD = -3.29, 95% CI -5.98, -.60, P = .02) for the subgroup with an age >= 60 years and that with >= 35 participants. In the subgroup analysis, result for SBP with a study duration >= 6 weeks was statistically significant different (WMD = -4.77; 95% CI -6.46, -3.08; P < .001). For an intervention dose of VitC >= 500 mg daily, SBP was statistically significant (WMD = -5.01; 95% CI -8.55, -1.48; P = .005). Conclusion: VitC supplementation resulted in a significant reduction of blood pressure in patients with essential hypertension.