A dose of vitamin C may give a quick boost to the poorer-than-average blood circulation seen in healthy young smokers, a study suggests. The study of 25 healthy men found that although smokers initially showed poorer results on a test of blood flow to the heart that changed after they took a large dose - 2 grams - of vitamin C.

Shortly after taking the vitamin, the 13 smokers showed blood circulation on par with that of the 12 non-smokers, according to findings published in a leading heart journal.

However, lest smokers think they can undo heart damage by chasing a cigarette with a vitamin C pill, the researchers say their findings underline the dangers of smoking.

Vitamin C is a potent antioxidant, a substance that helps clear the body of cell-damaging molecules called oxygen free radicals. Because of this, it's thought that the vitamin may counter the "oxidative stress" that smoking puts on the lining of the blood vessels - a mechanism by which smoking leads to artery disease.

The new study looked at the effect of oral vitamin C on coronary flow velocity reserve (CFVR), a measure of how well blood flow speeds up to help the heart when it's under high demands. Past research has shown that smokers show poorer blood-vessel dilation in response to blood flow, and have a diminished CFVR.

The research team used a non-invasive ultrasound technique to measure CFVR in smokers and non-smokers, before and after they took vitamin C. They found that before taking the vitamin, smokers had a lower CFVR than non-smokers did. Two and four hours after the dose of vitamin C, however, smokers' average CFVR was "restored" to a more-normal level.

Though the men in the study were given a large dose of vitamin C, researchers pointed out that it's probably useless to take doses beyond 200 milligrams, because the body will excrete the excess.

Moreover, it's not clear that loading up on vitamin C can benefit smokers. Some trials have found that taking C supplements does not improve smokers' blood vessel function, at least in the short term.

Researchers said further, large-scale trials should look at whether daily vitamin C supplements cut smokers' long-term risk of coronary artery disease.

Tanya Roberts is research associate, www.onlinesmoker.com