You may see media coverage about a study at Johns Hopkins that says people may be able to reduce blood pressure by taking large doses of vitamin C. However, the researchers stopped short of recommending starting large supplementation of vitamin C.
Edgar R. Miller III, associate professor and lead author of the study published in the American Journal of Clinical Nutrition, says the research suggests a modest blood pressure lowering effect with vitamin C supplementation. He says he will hold off recommending supplements as a treatment for high blood pressure until more research is done to understand the implications.
About 30 percent of adults in the United States have high blood pressure, or hypertension, an important risk factor for heart disease and stroke. Successful treatment may include drugs, exercise, weight loss and dietary changes such as reducing salt intake.
Miller’s team wants to find evidence-based guidance about whether supplements help or actually do harm.
Scientists have focused on vitamin C’s potential role in blood pressure reduction because of the nutrient’s biological and physiological effects. For example, vitamin C may act as a diuretic, causing the kidneys to remove more sodium and water from the body, which helps to relax the blood vessel walls, thereby lowering blood pressure.
Five hundred milligrams of vitamin C is the amount in about six cups of orange juice. The recommended daily intake of vitamin C for adults is 90 milligrams.
Some experts believe that large amounts of vitamin C, an essential micronutrient found primarily in fruits and vegetables, could lower pressure as well, but randomized, controlled dietary intervention studies — the gold standard of nutrition research — have produced mixed results.
Miller reviewed and analyzed data from 29 randomized, controlled, previously published clinical trials that reported systolic and/or diastolic blood pressure values and also compared vitamin C intake to a placebo. What they found is that taking an average of 500 milligrams of vitamin C daily — about five times the recommended daily requirement — reduced blood pressure by 3.84 millimeters of mercury in the short term. Among those diagnosed with hypertension, the drop was nearly 5 millimeters of mercury.
By comparison, Miller says, patients who take blood pressure medication such as ACE inhibitors or diuretics can expect a roughly 10 millimeter of mercury reduction in blood pressure.
Miller cautions, however, that none of the studies his team reviewed show that vitamin C directly prevents or reduces rates of cardiovascular disease, including stroke.