In a large cross-sectional study of survey data from U.S. youth under age 17, increases in the antioxidants serum beta-carotene and vitamin C, along with the trace mineral selenium which is also considered an antioxidant, were associated with a lower risk of asthma prevalence. Even stronger asthma reduction associations for the three antioxidants were found in subgroups of young people exposed to passive smoke. The researchers studied data from 6,153 young persons from 4 to 16 years old who were a part of the Third National Health and Nutrition Survey (NHAMES III). A household youth questionnaire, answered usually by the mother, was used for participants less than 17 years old. The study included a comprehensive health examination, together with various laboratory measurements. Using separate antioxidant models, the researchers said that serum vitamin E had little or no association with asthma. However, a standard deviation increase in beta-carotene was associated with a 10 percent reduction in asthma prevalence in those not exposed to smoke and a 40 percent reduction in young persons who had passive smoke exposure. The pattern for vitamin C was similar to beta-carotene results, according to the researchers. An increase in selenium was associated with a 10 to 20 percent decrease in asthma prevalence. In youth with passive smoke exposure, investigators found a 50 percent reduction in asthma prevalence associated with selenium. (In the diet, a high percentage of the trace element selenium is found in cereal grains, fish, meat, and poultry. Toxic effects have been reported among individuals who consumed excessive selenium supplements.) The study appears in the first issue for February 2004 of the American Thoracic Society's peer-reviewed American Journal of Respiratory and Critical Care Medicine.