CORVALLIS, Ore. - Researchers have discovered that a 500 milligram daily supplement of vitamin C can significantly reduce high blood pressure in hypertensive patients.
The study, published this month in the medical journal Lancet, was done by scientists at the Boston University School of Medicine and the Linus Pauling Institute at Oregon State University. It was supported by the National Heart, Lung and Blood Institute of the National Institutes of Health.
"Hypertension is a serious health problem in much of the world," said Balz Frei, professor and director of the Linus Pauling Institute, and a co-author of the research along with principal investigator Dr. Joseph Vita at Boston University. "It's a key risk factor in heart disease and strokes."
"We believe this is a significant finding that may be of considerable value to patients who have moderately elevated blood pressure," Frei said. "Working with their doctors, it may provide a way to bring their blood pressure back within acceptable levels without the cost or possible side effects of prescription drugs."
The amount of vitamin C used to produce the blood pressure reductions found in the study - 500 milligrams per day - would be without any side effects, very inexpensive as a dietary supplement, and could yield blood pressure reductions comparable to those of some prescription drugs used to reduce hypertension, the researchers said.
The vitamin C intake might also produce other health benefits as well, Frei said, especially if it was at least partially obtained by eating an improved diet rich in fruits and vegetables.
In this placebo-controlled, double-blind study, scientists worked with 45 patients with differing characteristics - different age, sex, race, smoker status, etc. - but who all had high blood pressure, defined as a diastolic blood pressure of more than 90 and a systolic blood pressure of more than 140 mm Hg. Some people who had more serious health problems such as diabetes or coronary artery disease were excluded. Patients who were taking medications to control their blood pressures discontinued those prescriptions long enough before tests were made so that they wouldn't seriously interfere with the results of the study.
An "acute" dosage of 2,000 milligrams of vitamin C was not found to have a significant immediate impact on blood pressure when it was measured two hours after the dose.
However, with the long term dosages of 500 milligrams of vitamin C per day, the systolic, diastolic and mean blood pressures all declined about 9 percent, measured one month after the vitamin C intake began. In general terms, this meant systolic pressure dropped from 155 to 142; diastolic from 87 to 79; and mean blood pressure from 110 to 100 mm Hg.
The drop in diastolic blood pressure was less statistically significant, Frei said, because in that measurement people taking placebo pills also had a modest drop in blood pressure. And intakes of vitamin C do not appear to have any effect in lowering the blood pressure of people whose levels are already normal.
In their report, the scientists said the mechanisms for the drop in blood pressure is still not certain.
"One theory that could explain the results is that vitamin C works as an antioxidant in the human body," Frei said. "In doing that, it would help protect the body's level of nitric oxide, which is important to blood vessel function."
Nitric oxide, he said, is a natural compound in the body that relaxes blood vessels and contributes to the body maintaining a normal, healthy blood pressure, Frei said. But under oxidative stress, nitric oxide may become inactivated or inhibited. An intake of vitamin C somewhat higher than normal may help protect the levels of nitric oxide and allow it to perform its natural functions, Frei said.
Other metabolic mechanisms may also be at work in this process which are not yet fully understood, the scientists said. And they caution that people with more seriously elevated blood pressure still need to incorporate medications or other lifestyle changes in close consultation with their doctors.
Confirmation of these findings in larger studies is recommended, the researchers said, although there already appears to be solid evidence from studies such as this and epidemiological analysis that vitamin C may have value in the clinical treatment of high blood pressure.
Related studies were also published last year in Circulation and other professional journals. In them, Frei, Vita and other scientists found that moderate daily supplements of vitamin C could improve endothelial function - the "relaxation" state of blood vessels - and thereby help prevent the chest pains of unstable angina pectoris and reduce the risk of heart attack and stroke. The dosage in that case - 500 milligrams per day - was the same as in the current research.
Frei and other experts at OSU's Linus Pauling Institute have also recently called for the recommended dietary allowance of vitamin C, even for healthy individuals, to be officially doubled to 120 milligrams per day, as evidence continues to emerge about the important health benefits it may have at higher levels than those once considered adequate to prevent the disease of scurvy.
A federal panel is at the moment considering these proposed changes for RDAs of vitamin C and other antioxidant vitamins.