PhotoThere are several things, besides medication, that can help you control your blood pressure. You can reduce sodium intake, get plenty of exercise and maintain a healthy weight.

There may be another, say researchers at Johns Hopkins: an increased intake of vitamin C. But while taking large doses of vitamin C may moderately reduce blood pressure, the researchers stopped short of suggesting people load up on supplements.

Modest effect

“Our research suggests a modest blood pressure lowering effect with vitamin C supplementation, but before we can recommend supplements as a treatment for high blood pressure, we really need more research to understand the implications of taking them,” said Edgar “Pete” R. Miller III, M.D., Ph.D., an associate professor in the division of general internal medicine at the Johns Hopkins University School of Medicine and leader of the study published in the American Journal of Clinical Nutrition.

Roughly 30 percent of adults in the United States have high blood pressure, or hypertension, an important risk factor for heart disease and stroke. Any new method of reducing, or moderating blood pressure would be viewed as a significant contributor to improved health. Randomized, controlled dietary intervention studies — the gold standard of nutrition research — have produced mixed results.

Reviewed 29 randomized trials

Miller and his colleagues reviewed and analyzed data from 29 randomized, controlled, trials that measured vitamin C's impact on blood pressure. 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.

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.

“Although our review found only a moderate impact on blood pressure, if the entire U.S. population lowered blood pressure by 3 milliliters of mercury, there would be a lot fewer strokes,” Miller said.

Controversy

The findings are not without some controversy. Nutritional supplements are a $28 billion-a-year industry, and marketing claims, newspaper stories and testimonials often make them hard to resist, Miller says.

People often view supplements as a “natural alternative” and preferable to drugs for high blood pressure or other ailments, he adds, despite mounting evidence that many supplements don’t work and in some cases may cause harm.

That's why Miller and his colleagues are advocating a cautious approach, with additional research to explore just how effective loading up on vitamin C really is.

“People love to take vitamins regardless of the evidence or lack of it,” Miller said. “We’re trying to raise the bar and provide evidence-based guidance about whether supplements help or actually do harm.” With respect to vitamin C, he says, the jury is still out.


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