Increasing vitamin C levels may have a favorable effect on high blood pressure. According to research appearing in the American Journal of Clinical Nutrition (1993;57:213-7), the concentration of vitamin C in the blood was inversely related to blood pressure. The higher the amount of vitamin C, the less likely the subject was to have high blood pressure. Smokers had significantly lower levels of vitamin C than non-smokers.
In the Journal of Hypertension (1991;9(11):1076-1077) an article noted that some epidemiologic studies have shown an inverse relationship between vitamin C intake and blood pressure. Vitamin C supplementation has lowered blood pressure in borderline hypertensive patients.
In a small study appearing in the journal Nutrition Research (2007; 27(2): 119-123), supplementation with vitamin C and garlic was able to lower blood pressure. There were only six subjects, with mildly elevated (140/90) blood pressure; but the supplementation was able to reduce blood pressure to normal. The subjects were treated for periods of ten days, then given a week off, before changing regimens. During one ten-day period they were given a placebo. Another ten-day period they were given 2000 mg per day of vitamin C. The other two ten day periods saw the subjects being supplemented with garlic and a vitamin C and garlic combination. Garlic lowered systolic blood pressure, but not diastolic pressure; while the combination of garlic and vitamin C lowered both. In this small study, vitamin C supplementation alone did not affect the blood pressure.