Vitamin C levels associated with asthma risk

Further evidence suggests that deficiency in vitamin C could
increase the likelihood of children developing asthma.

Higher levels of the vitamin, as well as the antioxidant beta-carotene and trace mineral selenium, were associated with a lower risk of asthma in a large study by Cornell researchers published earlier this year.

The new study by a team at Johns Hopkins University School of Medicine in Baltimore shows that children with asthma tended to have lower blood levels of vitamin C than children with healthy lungs.

But the team cautioned that antioxidant levels may be surrogate markers for socioeconomic variables such as race, poverty, tobacco exposure, or general nutritional status.

The study, published in the February 15 issue of the American Journal of Epidemiology, is based on data from the Third National Health and Nutrition Examination Survey (NHANES III), conducted in the United States between 1988 and 1994. The authors selected 4,093 children (aged 6-17 years), with 9.7 per cent of these diagnosed with asthma.

Initial analyses showed that asthma was associated with lower levels of serum vitamin C, beta-carotene, and beta-cryptoxanthin. But in logistic models that included age, body mass index, socioeconomic variables, antioxidant levels, parental asthma, and household smoking, the only antioxidants significantly associated with asthma were vitamin C and beta-carotene.

The odds ratio for asthma in the highest quintile of serum vitamin C relative to the lowest was 0.65, whereas it was 0.74 for beta-carotene.

Vitamin C and other antioxidants are thought to fight oxidation, thought to be a factor in disease.