BALTIMORE—Vitamin C supplementation reduced both systolic and diastolic blood pressure, at least in short-term trials, according to a new meta-analysis from Johns Hopkins School of Medicine (Am J Clin Nutr. 2012 Apr 4).

The systematic review and meta-analysis included clinical trials researchers found by searching Medline, EMBASE and Central databases from 1966 to 2011. To be included in the analysis, studies must have been randomized controlled trials at least two weeks long focusing on effects on systolic blood pressure or diastolic blood pressure or both using oral vitamin C and concurrent control groups.

The researchers included 29 trials tfor the primary analysis with a median dose of 500 mg/d (about five times the recommended daily requirement), a median duration of eight weeks, and trial sizes ranging from 10 to 120 participants.

The pooled changes in systolic blood pressure and diastolic blood pressure were -3.84 mm Hg (P<0.01) and -1.48 mm Hg (P=0.04), respectively. In trials with hypertensive participants, corresponding reductions in systolic blood pressure and diastolic blood pressure were -4.85 mm Hg (P<0.01) and -1.67 mm Hg (P=0.17). By comparison, author leader Edgar “Pete” R. Miller III, M.D., Ph.D.,  said patients who take blood pressure medication such as ACE inhibitors or diuretics can expect a roughly 10 millimeter of mercury reduction in blood pressure.

After the inclusion of nine trials with imputed blood pressure effects, blood pressure effects were attenuated, but remained significant.

“Although our review found only a moderate impact on blood pressure, if the entire U.S. population lowered blood pressure by 3 ml of mercury, there would be a lot fewer strokes,” said Miller, associate professor in the division of general internal medicine at the Johns Hopkins University School of Medicine. Miller cautioned, however, that none of the studies his team reviewed show that vitamin C directly prevents or reduces rates of cardiovascular disease (CVD), including stroke.

“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,” Miller said.

Roughly 30 percent of adults in the United States have high blood pressure, or hypertension, an important risk factor for heart disease and stroke.