Many epidemiological studies and some clinical trials have indicated that dietary intake of or supplementation with vitamin C is associated with a reduction in the incidence of chronic disease morbidity and mortality, including cardiovascular diseases. Numerous epidemiological studies have shown a significantly decreased heart attack or stroke risk with increased vitamin C intake. Although this study indicated that vitamin C supplements provide cardiovascular benefits above and beyond the vitamin C obtained from the diet, two other large epidemiological studies published in 1996 found no effect on heart disease risk in people who take regular vitamin C supplements. However, not a single epidemiological study nor clinical trial has found an increased risk of heart attacks or strokes in people taking vitamin C supplements. Over twenty clinical studies since 1996 published primarily in Circulation have consistently found beneficial effects of vitamin C, administered either orally or by intra-arterial infusion, on the relaxation of arteries, or vasodilation.
Impaired vasodilation is an important risk factor for heart attacks and strokes.
Vasodilation in patients with heart disease is significantly improved following supplementation with 500 mg of vitamin C per day for 30 days, and is comparable to vasodilation seen in healthy people. Beneficial effects of vitamin C supplements leading to normalization of vasodilation were also observed in patients with angina, heart failure, high cholesterol levels, hypertension, diabetes, high homocysteine levels and in smokers. In addition, a recent study in Lancet has demonstrated that 500 mg of vitamin C per day given for 30 days lowers blood pressure in moderately hypertensive patients. High blood pressure is a major risk factor for heart disease. Several limitations of the study reported by Dwyer and colleagues need to be pointed out.