Association between Serum Vitamin C and the Blood Pressure: A Systematic Review and Meta-Analysis of Observational Studies

BACKGROUND: Hypertension is regarded as a major and independent risk factor of cardiovascular diseases, and numerous studies observed an inverse correlation between vitamin C intake and blood pressure. AIM: Our aim is to investigate the relationship between serum vitamin C and blood pressure, including the concentration differences and the correlation strength. METHOD: Two independent researchers searched and screened articles from the National Library of Medicine, Cochrane Library, Web of Science, China National Knowledge Infrastructure, VIP databases, and WANFANG databases. A total of 18 eligible studies were analyzed in the Reviewer Manager 5.3 software, including 14 English articles and 4 Chinese articles. RESULTS: In the evaluation of serum vitamin C levels, the concentration in hypertensive subjects is 15.13 μmol/L lower than the normotensive ones (mean difference = −15.13, 95% CI [-24.19, -6.06], and P = 0.001). Serum vitamin C has a significant inverse relation with both systolic blood pressure (Fisher′s Z = −0.17, 95% CI [-0.20, -0.15], P < 0.00001) and diastolic blood pressure (Fisher′s Z = −0.15, 95% CI [-0.20, -0.10], P < 0.00001). CONCLUSIONS: People with hypertension have a relatively low serum vitamin C, and vitamin C is inversely associated with both systolic blood pressure and diastolic blood pressure.