In observational studies, increased vitamin C intake, vitamin C supplementation, and higher blood concentrations of vitamin C are associated with lower blood pressure (BP). This systematic review and meta-analysis evaluated clinical trials that examined the effects of vitamin C supplementation on BP. Twenty-nine trials were included and the median vitamin C dose was 500 mg per day, the median duration was 8 weeks, and trial sizes ranged from 10 to 120 participants. The results showed that vitamin C supplementation reduced systolic and diastolic BP. The authors conclude "Long-term trials on the effects of vitamin C supplementation on BP and clinical events are needed".
Juraschek SP, Guallar E, Appel LJ, Miller ER 3rd. Effects of vitamin C supplementation on blood pressure: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2012 May;95(5):1079-88.