Serum levels of vitamin D in more than 600 Costa Rican children were inversely linked to several indicators of allergy and asthma severity, including hospitalizations for asthma, use of inhaled steroids and total IgE levels, according to a study that will appear in the first issue for May of the American Journal of Respiratory and Critical Care Medicine.
While previous in vitro studies have suggested that vitamin D may affect how airway cells respond to treatment with inhaled steroids, this is the first in vivo study of vitamin D and disease severity in children with asthma.
Juan Celedon, M.D., Dr. P.H. and Augusto Litonjua, M.D., M.P.H. of Harvard Medical School and colleagues recruited 616 children with asthma living in the Central Valley of Costa Rica, a country known to have a high prevalence of asthma. Each child 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 percent of the predicted value were also tested for airway reactivity.
They found 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 signifying 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 Drs. Celedon 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 suggests that there may be added health benefits to vitamin D supplementation" said Dr. Celedon. Current recommendations for optimal vitamin D levels geared toward preserving bone health, such as preventing rickets in children and osteoporosis in adults.