Low Vitamin C May Up Asthma Risk

Children with low levels of vitamin C may be more likely to develop asthma, researchers report.

In a nationwide study, children with asthma tended to have lower blood levels of the vitamin than children with healthy lungs. Despite this association, however, it is too soon to say that a lack of adequate vitamin C causes asthma, the study's lead author told Reuters Health.

"These results, along with results from other studies, support the hypothesis that certain vitamins may prevent or ameliorate asthma," Dr. Robert A. Wise of Johns Hopkins University School of Medicine in Baltimore told Reuters Health.

But Wise cautioned that the findings do not prove that vitamin supplements can prevent or treat asthma.

"Vitamin C may only be a marker for other unmeasured micronutrients or exposures," he said. Clinical trials will be necessary to determine whether vitamin C can prevent or treat asthma.

Vitamin C and other antioxidants target a process called oxidation in which cell-damaging substances called free radicals accumulate. Scientists have been interested in finding out whether antioxidants influence the effect of oxidation and inflammation in the lungs and airways.

To investigate a possible link between antioxidants and asthma, Wise's team evaluated information from more than 4,000 children in a national health survey. Results of the study appear in the American Journal of Epidemiology.

All children in the study underwent testing to measure blood levels of vitamins A, C and E. Levels of antioxidants called carotenoids, a group of compounds that produce the red, yellow and orange colors found in many fruits and vegetables, were also measured.>

Wise's team found that children with lower levels of vitamin C and carotenoids were more likely to have asthma. Only vitamin C and a carotenoid called alpha-carotene were associated with asthma risk, however, once researchers accounted for things that are known to influence asthma risk, such as age, obesity, socioeconomic level, parental asthma and exposure to secondhand smoking.

Despite the association between blood levels of vitamin C and asthma risk, children with and without asthma did not differ significantly in the amount of vitamin C they consumed, according to the report.

One possible explanation, the authors suggest, is that the surveys used to measure vitamin intake were not accurate. Another possibility is that vitamin C may be processed differently in children with asthma, which may lead to reduced blood levels of the vitamin.

SOURCE: American Journal of Epidemiology, February 15, 2004.