NEW YORK (Reuters Health) - Smokers who take vitamin C can restore their blood levels of the antioxidant, but taking the vitamin does not reverse the abnormal blood vessel function seen in tobacco-users, researchers report.

Smoking disrupts the normal function of the lining of arteries, known as the endothelium, which must contract and relax to regulate blood flow. This abnormal function can promote atherosclerosis, thereby increasing the risk of heart attack and stroke, according to Dr. Olli T. Raitakari from Royal Prince Alfred Hospital in Sydney, Australia, and colleagues. Because vitamin C has been shown to reduce some of the damage to the arteries caused by cigarette smoke, the researchers randomly assigned 20 otherwise-healthy cigarette smokers to take vitamin C or an inactive (placebo) pill daily for 8 weeks. All 20 smokers had abnormal endothelial function at the beginning of the study, according to the report in the May issue of the Journal of the American College of Cardiology. During the study, smokers who took vitamin C doubled their blood level of the antioxidant from an abnormally low level to a mid-normal range. When it came to endothelial function, the investigators found that a single dose of vitamin C doubled the response of blood vessels to a blood vessel-dilating drug. However, after 8 weeks of vitamin C treatment, the blood vessel response had returned to its abnormally low level. ``In summary, short-term oral administration of antioxidant vitamin C markedly improved endothelial function in smokers, but there was no significant beneficial effect observable after a further 8 weeks of treatment,'' Raitakari and colleagues conclude. ``The lack of sustained effect,'' the authors add, ''...discourages the daily use of vitamin C for vascular protection in smokers with established endothelial dysfunction.''

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