Study finds vitamin C lowers blood pressure

In the May 2012 issue of The American Journal of Clinical Nutrition, Hopkins researchers led by Stephen Juraschek from the School of Medicine found another benefit of vitamin C that gives the little molecule an even better name.

Vitamin C is an organic compound derived from glucose and is an essential nutrient for almost all animals. Most people know it can be found readily in fruits such as oranges and grapefruits and has roles as an antioxidant and booster of the immune system. Because of its many benefits, the compound has been widely studied in the past and people often take vitamin C supplements on a regular basis.

However, there has been controversy about the vitamin’s ability to lower blood pressure. “Over the past 50 years over 30 randomized, clinical trials have examined the effect of vitamin C on blood pressure with mixed results,” Juraschek wrote in an e-mail to The News-Letter.

“Many of the trials were small and of short duration. By summarizing the trial findings our hope was to help clarify whether or not vitamin C could be used to lower blood pressure.”

Based on their findings after reviewing 29 previously published studies on vitamin C intake, Juraschek and his team found that taking about 500 milligrams of vitamin C a day could reduce blood pressure by 3.84 mmHg.

While the number seems small, a blood pressure level of 140/90 mmHg is considered high, meaning vitamin C could lower it by 2-4%. Comparatively speaking, medications meant to lower blood pressure typically reduce pressure by about 10 mmHg. The relative low cost and ease of taking vitamin C supplements therefore offers a small step towards building a healthier lifestyle.

As the team from Hopkins began to assemble their findings, the data truly surprised them. “Although as we went through the trials it seemed probable that vitamin C exerted a blood pressure reducing effect, we did not anticipate it would be so robust,” Jurascheck wrote. “Even after conservatively imputing effects of trials that did not report their vitamin C findings, we still found a significant overall reduction in systolic and diastolic blood pressure.”

It is believed that vitamin C lowers blood pressure by acting as a diuretic, aiding the kidneys in removing water from blood and allowing the vessels to relax.

Despite the positive findings, Juraschek urges that his work should not be taken out of context and become a new marketing tool for companies looking to sell vitamin C supplements. He is quick to point out that many of the studies failed to control for other factors such as the use of other antioxidants or blood pressure medications in conjunction with vitamin C.

“Prior to conducting our systematic review, we agreed as a research team on a number of trial characteristics that we thought should not be pooled together. The presence or absence of additional supplements in the intervention was not one of these characteristics,” Jurascheck wrote, when asked why these factors were included in the study.

However, to ensure a more accurate and complete study, Jurasheck and his team expanded their research by narrowing the field of studies included.

“We did explore this design issue in a stratified analysis and did not see a significant difference between trials that gave vitamin C alone or in combination with other agents,” he wrote.

Juraschek acknowledged that the topic certainly requires more research before any definitive conclusions can be made. In the future, he and his team will be looking to conduct their own research in order to paint a clearer picture on the various effects vitamin C can have on the body.