Previous population studies have found an association between with decreased intakes of antioxidants such as vitamin C and incidence of asthma although follow-up studies looking particularly at vitamin C have produced conflicting results.
The new study, published in the August issue of the European Respiratory Journal (vol 26, no2), investigated the possibility that decreased levels of antioxidants may also contribute to the development of severe asthma.
Neil Misso from the Asthma & Allergy Research Institute in Australia and his colleagues compared the dietary intakes and blood concentrations of antioxidants, including vitamin C, in 28 patients with severe asthma compared with 53 mild asthmatic patients and 43 subjects without asthma.
Among all subjects the dietary intakes of vitamin C and carotene, which are mainly derived from fruit and vegetables, were lower in males than in females.
Men with severe asthma had a particularly low intake of these antioxidants.
The blood concentrations of vitamin C were markedly lower in patients with severe asthma compared to subjects with mild asthma or those without asthma, and this difference was observed in both males and females, said the researchers.
The study also identified patients with severe asthma as being more overweight, with a higher intake of fat and a higher blood cholesterol concentration compared with the other subjects.
In addition, lung function was better in subjects with high blood vitamin C and low blood cholesterol concentrations.
The study suggests that patients, and particularly males, with severe asthma may benefit from making sure they have an adequate intake of antioxidants such as vitamin C in their diet.
The researchers noted that in a recent trial, children with mild asthma found no benefit from taking vitamin C.
But they write that "the results of the present study, together with recent evidence that the beneficial effects of antioxidants may be influenced by polymorphisms in the glutathione S-transferase gene, indicate that there is a need for further trials of vitamin C supplementation in patients with more severe asthma".
If confirmed in future trials, taking supplements or vitamin-rich foods could be a relatively easy strategy to help decrease the morbidity and socioeconomic burden associated with severe asthma, said the researchers.
In the UK, one in eight children has asthma and this figure has increased six-fold in the last 25 years, according to Asthma UK.