ASCORBIC-ACID AND DEHYDROASCORBIC ACID AS BIOMARKERS OF OXIDATIVE STRESS CAUSED BY SMOKING

Using a reliable, newly developed assay for ascorbic acid (reduced for m) and dehydroascorbic acid (DHAA; the oxidized form) in plasma, we st udied the influence of age, sex, and smoking on 219 healthy, age-strat ified, and randomly selected subjects representing the Danish populati on. The mean (+/- SD) plasma total ascorbic acid (ascorbic acid + DHAA ) concentration was lower in smokers (62.8 +/- 24.9 mu mol/L) than in nonsmokers (74.9 +/- 23.6 mu mol/L) (P < 0.001) and the DHAA content w as 1.8 +/- 4.0% of the total ascorbic acid in smokers compared with 0. 1 +/- 3.1% in nonsmokers (P < 0.001). A significant inverse correlatio n between the DHAA fraction and the total ascorbic acid concentration was found in smokers (P < 0.002) but not in smokers; the slopes of the linear regressions were significantly different in the two groups (P < 0.005). The mean plasma concentration of total ascorbic acid was hig her in females than in males (P < 0.005); this difference persisted in multivariate analysis when smoking was adjusted for. No age dependenc e could be identified. The data show that smoking results in severe ox idative stress, depletion of the ascorbic acid pool, and insufficient reduction capacity to maintain ascorbic acid in the reduced form in pl asma. We suggest that the additional analysis of DHAA allows further d ifferentiation in the assessment of oxidative stress and may provide a n objective way of determining vitamin C requirements in smokers. Prel iminary findings suggest that a vitamin C dose that results in a plasm a concentration of approximate to 70 mu mol/L or higher is required in smokers.