Some Antioxidants Higher, Lower in Hypertensives

Fri Jan 3, 2003

By Natalie Engler

NEW YORK (Reuters Health) - People with hypertension tend to have higher blood levels of vitamins A and E and lower levels of antioxidants such as vitamin C and beta carotene when compared with those without high blood pressure, US researchers report.

The results support other studies that found that vitamin E does not reduce the risk of blood pressure or heart disease, according to the report, but contradicts two others that suggested vitamin A might be helpful.

The large national study found that blood pressure rose in tandem with blood levels of vitamins A and E regardless of age, gender, race and lifestyle.

Taken together, the research raises questions about the widespread use of supplements, study author Dr. Jiang He told Reuters Health in an interview.

"We should not recommend that patients (who already have high blood pressure) take vitamins A and E," he said.

However, vitamin C, alpha carotene and beta carotene, which the body converts to vitamin A, were associated with a lower risk of high blood pressure, researchers report in the December issue of Hypertension: Journal of the American Heart Association (news - web sites).

Antioxidants neutralize cell-damaging compounds called free radicals, which have been linked to the development of heart disease and cancer. Some experts believe these nutrients could help fend off such conditions.

In the current study, investigators at Tulane University in New Orleans, Louisiana examined levels of antioxidants in the blood in relation to blood pressure among more than 15,000 adults participating in the Third National Health and Nutrition Examination Survey.

People who reported taking vitamin supplements showed higher blood levels of the vitamins they consumed.

Dr. Jeffrey Blumberg, an antioxidant researcher at Tufts University School of Medicine in Boston, notes that the study is the first to find an association between blood pressure and alpha and beta carotene, "so if this is real or significant then it needs to be replicated."

It's possible that carotenes, which are found in fruits and vegetables, are simply a proxy measure for some other dietary factor that could influence blood pressure, said Blumberg, who was not involved in the study. Other studies have shown a link between vitamin C and blood pressure, so "it's a confirmation of what we already know," he said.

"Obviously there are other factors going on. It would be conservative to say that there does appear to be a role of antioxidants in blood pressure regulation but we're not quite clear what it is or what dose or what diet is the optimal for doing this," said Blumberg.

"I would point out importantly that none of these are huge increases or decreases, I mean the impact of antioxidants on blood pressure whether up or down, real or not, are pretty modest," he said.

"In my view these findings suggest that they play some role, but probably not wildly important, I think they will probably be found to contribute modestly."

SOURCE: Hypertension 2002;40:810-816.

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