Several studies have found that vitamin C over several years does seem to slowly lower blood pressure. It doesn’t seem to have much effect over the short term, but over years it may make a difference. I’ve studied the history of Linus Pauling promoting vitamin C as wonder drug, and life extension for cancer patients. Shortly after NCI (National Cancer Institute) declared that Vit. C. was a bust a careful study by Japanese researchers (Morishige & Murate) found that cancer patients on Vit. C. mega doses lived more than 5 times longer than the controls. Thus, I consider the Vit C issue still very much an open medial question. Most of the convincing studies on Vit C effectiveness against infection and cancer involve intravenously given Vit C — which raises the question Does oral vitamin C have much effectiveness? And does oral Vitamin C in low doses work against colds, infections and high blood pressure? Personally I try to eat foods that are high in natural vitamin C, and in times of illness (cold or flu) often take oral vitamin C. It seems to help — perhaps it is Placebo effect, perhaps it is something more real.
http://www.sciencedaily.com/releases/1999/12/991221080724.htm
http://www.yourhealthbase.com/hypertension.html
http://www.healthy.net/Health/Article/Linus_Pauling_and_Vitamin_C_Therapy_for_Breast_Cancer/1243/1