Edgar "Pete" Miller III, MD, PhD, Associate Professor of Internal Medicine at the Johns Hopkins University School of Medicine and colleagues made a systematic review of vitamin C trials published between 1966 and 2011. They found that supplementation with the vitamin produces a modest but consistent and measurable reduction in blood pressure.
An essential micronutrient acquired primarily from fruit, vegetables or supplements, vitamin C is a powerful aqueous-phase antioxidant that reduces oxidative stress and enhances endothelial function through the effects on nitric oxide production. Oxidative stress has been linked to certain cardiovascular diseases, playing a role in both strokes and heart attacks. These correlations have led some researchers to postulate that supplementation may reduce CVD.
Dr. Miller's review showed that supplementation with 500 milligrams of vitamin C daily – about five times the recommended daily requirement – reduced systolic and diastolic blood pressure by -3.84 millimeters and -1.48 millimeters of Hg, respectively, in the short term. Though small, these changes were statistically significant (Juraschek SP, et al. Am J Clin Nutr. 2012; 95(5): 1079-88)
By comparison, Dr. Miller says patients who take medications such as ACE inhibitors or diuretics, can expect BP reductions in the range of 10 mmHg.
The mechanistic studies showed that ascorbate (Vitamin C), increases intracellular concentrations of tetrahydrobiopterin, a cofactor of endothelial nitric oxide synthase, which enhances production of nitric oxide – a potent vasodilator. Vitamin C supplementation appears to improve endothelial function of both brachial and coronary arteries.
Though the findings are intriguing, Dr. Miller said it is premature to say that vitamin C has a definite role in treatment of hypertension. The data should not be construed to mean that vitamin C supplementation could be a substitute for hypertensive medications.
A healthy diet is still a patient's best bet for reducing blood pressure and consequent CVD risk. Dr. Miller noted that patients who improved their diets had more success in lowering their blood pressure than those who didn't.
A diet high in fruits and vegetables with the right amount of protein, such as the DASH Diet, is an effective way to add necessary nutrients. Adding foods with high amounts of calcium, potassium and magnesium has been proven to lower blood pressure and cholesterol.
Though moderate supplementation may confer some benefit, too much vitamin C can cause a build up of uric acid in the kidneys, which can cause kidney stones.
"With respect to Vitamin C, the jury is still out," Dr. Miller told Holistic Primary Care. More long-term trials on the effects of vitamin C on BP and clinical events are needed." Vitamin C can, however, be recommended for the prevention of hypertension or as adjuvant antihypertensive therapy.
Vitamin C supplementation---just like drug therapy--will be most effective when combined with dietary changes, exercise, and when appropriate, a weight loss program.