Smoking away vitamin C.

Cigarette smoking seems to deplete vitamin C levels in the blood. Realizing this, the National Research Council in 1989 revised smokers' recommended daily allowance (RDA) for vitamin C, raisinsg it from 60 milligrams--the RDA for the general population--to 100 mg. But a new study suggests the revised RDA for this vitamin still falls far short of providing smokers the same benefits that non-smokers get from the general RDA.

As the body's premier scavenger of potentially damaging oxidants and highly reactive molecules called free radicals (SN: 8/26/89, p. 133), vitamin C may assist in such important functions as protecting against carcinogens, boosting immunity and preventing heart-disease-fostering changes in fats.

Two years ago, a team led by Gordon Schectman at the Medical College of Wisconsin in Milwaukee published findings suggesting that more than one-quarter of U.S. smokers suffer marginal to severe vitamin C deficiencies. The same team has now studied data on 11,582 people who participated in the second National Health and Nutrition Examination Survey, comparing diets with blood levels of vitamin C. The new findings indicate smokers need more than 200 mg of vitamin C daily in order to lower their risk of deficiency (less than 23 micromoles of vitamin C per liter of blood serum) to the same level as that of nonsmokers consuming 60 mg.

The data show that about 57 percent of nonsmokers eat diets that fulfill their RDA from vitamin C. However, only 27 percent of smokers meet the revised, 100-mg RDA, and only 9 percent consume more than 200 mg per day, the researchers report in the June AMERICAN JOURNAL OF CLINICAL NUTRITION.

For smokers, they conclude, "vitamin supplementation may be necessary to reduce the prevalence of low serum concentrations of vitamin C to rates acceptable in nonsmokers."