Serum levels of vitamin D were inversely linked to several indicators of allergy and asthma severity, including hospitalizations for asthma, use of inhaled steroids, and total IgE levels in more than 600 Costa Rican children in a recent study.

Previous in vitro studies have suggested that vitamin D may affect how airway cells respond to treatment with inhaled steroids, but, this is the first in vivo study of vitamin D and disease severity in children with asthma.

Researchers Juan Celedón, MD, Dr PH and Augusto Litonjua, MD, MPH of Harvard Medical School and colleagues conducted their research in Central Valley of Costa Rica because the country is known to have a high prevalence of asthma. The study included 616 children with asthma living in the area. Each participant was assessed for allergic markers, including both allergen-specific and general sensitivity tests, and assessed for lung function and circulating vitamin D levels. Children whose forced expiratory volume in one second (FEV1) exceeded 65% of the predicted value were also tested for airway reactivity.

According to a release on the study, results showed that children with lower vitamin D levels were significantly more likely to have been hospitalized for asthma in the previous year, tended to have airways with increased hyperreactivity, and were likely to have used more inhaled corticosteroids: all indicators of higher asthma severity. These children were also significantly more likely to have several markers of allergy, including dust-mite sensitivity.

"To our knowledge this is the first study to demonstrate an inverse association between circulating levels of vitamin D and markers of asthma severity and allergy," wrote Celedón and Litonjua. "While it is difficult to establish causation in a cross-sectional study such as this, the results were robust even after controlling for markers of baseline asthma severity."

"This study also provides epidemiological support for a growing body of in vitro evidence that vitamin D insufficiency may worsen asthma severity, and we suspect that giving vitamin D supplements to asthma patients who are deficient may help with their asthma control," wrote Celedón and Litonjua, noting that a clinical trial should be the next step in this research. "Whether vitamin D supplementation can prevent the development of asthma in very young children is a separate question, which will be answered by clinical trials that are getting under way.”

"This study suggests that there may be added health benefits to vitamin D supplementation," said Celedón.

Currently, recommendations for optimal vitamin D levels are geared toward preserving bone health, such as preventing rickets in children and osteoporosis in adults.

The study appears in the first issue for May of the American Journal of Respiratory and Critical Care Medicine.