LONDON, 13 September (SPIS MedWire). The pro-oxidant effect of cigarette smoke extends to the coronary microcirculation, thereby reducing myocardial blood flow, concludes a multicenter clinical trial published 12 September (Circulation 2000, 102:1233-1238). A second finding from the same study is that coronary flow is restored by administration of the antioxidant vitamin C. The researchers used positron emission tomography to measure coronary flow reserve – an integrated measure of coronary flow – in 11 smokers and eight control subjects before and after administration of vitamin C. At baseline, coronary flow reserve was reduced by 21% in smokers compared with control subjects (p<0.05) but was normalized after vitamin C, whereas the drug had no effect in control subjects. Short-term infusion of vitamin C, the team reports, "almost completely reverses microcirculatory dysfunction in asymptomatic smokers." These results suggest that increased productivity or activity of oxygen-derived free radicals contributes to vascular damage and heart disease in chronic smokers. The team say their finding that vitamin C restores coronary microcirculatory responsiveness and impaired coronary flow reserve in smokers "provides evidence that the damaging effect of smoking is at least in part accounted for by an increased oxidative stress." They also suggest that the larger amount of vitamin C in the Mediterranean diet "could contribute to the fact that in northern Europe the absolute risk of coronary artery disease is higher than in the Mediterranean area, despite the higher prevalence of smoking among Mediterranean populations." The present study sheds no light on the long-term effects of vitamin C, or on whether oral vitamin C supplementation has preventive effects on the development of coronary artery disease, and the authors call for large-scale trials to investigate these unknowns.