Dec. 10, 1999 (Indianapolis) -- Studies have shown that increased dietary intake of vitamin C is related to lower blood pressure (BP) readings. A new study in the Dec. 11 issue of the journal The Lancet shows similar results.
"We are interested in the effects of vitamin C on coronary heart disease," says author Joseph A. Vita, MD, who is associate professor of medicine at the Boston University School of Medicine, in an interview with WebMD. "We published another study earlier this year that observed some beneficial effects, including dilation of the blood vessels, in people taking vitamin C. We were also intrigued by the literature that suggests the amount of vitamin C in the diet actually influences blood pressure, with the more vitamin consumed, the lower the blood pressure."
Forty-five otherwise healthy patients with a history of high blood pressure were enrolled in the study. Following a 2 g dose of vitamin C on the first visit, they were given either placebo or 500 mg a day of vitamin C. Medications to treat high BP were withheld for either 12 or 24 hours prior to two visits, one month apart. Otherwise, regular medications were continued through the time period. Patients were told to fast overnight and not smoke for 24 hours prior to the visits.
Systolic BPs (the higher number) in the two groups were similar in the beginning and at two hours after the initial dose. Following one month of vitamin C use, average systolic pressure had fallen for the subjects who were taking the vitamin C, whereas the placebo had no effect. Vitamin C concentrations in the blood were similar at the beginning of the study between the two groups and increased in the vitamin C group at both two hours and one month. There was an inverse correlation between the change in average BP and the change in vitamin C concentrations. This means that as the amount of vitamin C in the blood goes up, the person's BP goes down.
"Vitamin C is a safe medicine with almost no known side effects," says Vita. "This is potentially a new treatment that people with high blood pressure might add under the direction of their doctor. Since we do yet know if this effect can be sustained for periods longer than 30 days, I certainly would not want any patients to stop taking their blood pressure medicines based on this report."
William G. Haynes, MD, assistant professor of internal medicine at the University of Iowa, says in an interview with WebMD that while BP was reduced, other major concerns in hypertension care, such as impact on the risk of death or stroke, were not measured. He also is concerned about how little is known about the long-term consequences of taking vitamin C at levels several times the adult recommended daily requirement.
"They are giving doses that are much higher than the recommended daily requirement of vitamin C and more than eight times that seen in a standard multivitamin," says Haynes, who was asked to give an independent view of the study. "We just don't know yet what the side effects might be at that level."
- A new study shows that taking vitamin C supplements, in the form of ascorbic acid, can lower blood pressure.
- The trial lasted only 30 days, so it is unknown whether vitamin C could be an effective long-term treatment.
- One criticism of the study is that the dose of vitamin C used to lower blood pressure is several times the recommended daily allowance, so side effects at that level are not known.