Vitamin C helps smokers maintain vitamin E levels
in smokers, a group at risk of low vitamin E levels due to higher
oxidative stress, by 45 per cent.
The results suggest smokers and non-smokers exposed to second-hand smoke could benefit from daily intake of vitamin C supplements although expert advice is clearly to avoid tobacco smoke altogether.
One in three Europeans are smokers, while the US figure is one in five. Tobacco smoke contains over 4,000 compounds, of which 60 are known carcinogens. The oxidative stress levels of smokers are significantly greater than non-smokers, and as such there is a bigger drain on the levels of antioxidants in the body.
Vitamin E, an antioxidant, actually refers to a group of eight compounds: four types of tocopherols and four tocotrienols. The most common form consumed in the diet is gamma-tocopherol, while alpha-tocopherol is the form mostly found in supplements.
"Supplementation with ascorbic acid [vitamin C] for two weeks effectively reduced the elevated plasma alpha- and gamma-tocopherol disappearance rate observed in cigarette smokers," wrote lead author Richard Bruno from Oregon State University.
The results of the double-blind, placebo-controlled randomized crossover study, published in the February issue of Free Radical Biology and Medicine (Vol. 40, pp. 689-697), followed eleven smokers and 13 non-smokers with an average age of 22, were assigned either a vitamin C supplement (500 mg, twice a day) or a placebo (70.5 per cent calcium phosphate, 29.5 per cent cellulose, and 0.5 per cent magnesium stearate for 17 days.
"During the placebo trial, smokers' alpha-tocopherol fractional disappearance rate were about 65 per cent faster than non-smokers," explained the researchers.
After about two weeks of vitamin C supplements the disappearance of alpha-tocopherol by 25 per cent, regaining vitamin E rates as those found in non-smokers.
"Thus, ascorbic acid supplementation restored smokers' alpha-tocopherol disappearance kinetics to "normal"," wrote Bruno.
The data adds to the understanding that increased levels of oxidative species in tobacco smoke increase the oxidative damage to tocopherols, and contribute to the significant disappearance.
The researchers suggest that the vitamin C works, not by preventing lipid peroxidation that would lead to oxidative stress, but by reducing an oxidized tocopherol moiety.
The study did not agree with previous reports that antioxidant supplements reduced the level of a marker of oxidative stress, F2-alpha-isoprostane. However, the researchers of the newer study proposed that the short duration, small sample size and younger participants may have affected this marker.
The overall picture from this small, short-term study does agree with the other studies in so far as vitamin C can help reduce the disappearance of vitamin E due to tobacco smoke.
"It would seem necessary for smokers to strive to consume a diet that contains at least the RDAs for vitamin E (15mg per day of alpha-tocopherol) and vitamin C (125 and 110 mg per day for male and female smokers, respectively).
In addition, further trials are warranted to determine if other dietary antioxidants can attenuate alpha- and gamma-tocopherol disappearance," concluded Bruno.
Vitamin E has been reported to protect against prostate cancer, although the evidence is sometimes contradictory and complicated by other reports linking the vitamin to increased risk of heart problems and all-cause mortality.