Low levels of vitamin D are linked to lower lung function and greater medication use in children with asthma, according to a study.
Researchers, led by Dr. Daniel Searing at National Jewish Health, also reported that vitamin D enhances the activity of corticosteroids, the most effective controller medication for asthma.
"Asthmatic children in our study who had low levels of vitamin D were more allergic, had poorer lung function and used more medications. Conversely, our findings suggest that vitamin D supplementation may help reverse steroid resistance in asthmatic children and reduce the effective dose of steroids needed for our patients," said Searing.
The researchers analysed electronic medical records of 100 pediatric asthma patients referred to National Jewish Health.
Overall, 47 percent of them had vitamin D levels considered insufficient, below 30 nanograms per milliliter of blood (ng/mL).
Seventeen percent of the patients had levels below 20 ng/mL, which is considered deficient.
The levels were similar to vitamin D levels found in the general population.
Patients low in vitamin D generally had higher levels of IgE, a marker of allergy, and responded positively to more allergens in a skin prick test. Allergies to the specific indoor allergens, dog and house dust mite, were higher in patients with low vitamin D levels.
Low vitamin D also correlated with low FEV1, the amount of air a person can exhale in one second, and lower FEV1/FVC, another measure of lung function.
Use of inhaled steroids, oral steroids and long-acting beta agonists were all higher in patients low in vitamin D.
"Our findings suggest two possible explanations. It could be that lower vitamin D levels contribute to increasing asthma severity, which requires more corticosteroid therapy. Or, it may be that vitamin D directly affects steroid activity, and that low levels of vitamin D make the steroids less effective, thus requiring more medication for the same effect," said senior author Dr. Donald Leung.
The researchers performed a series of laboratory experiments that indicated vitamin D enhances the action of corticosteroids.
"Our work suggests that vitamin D enhances the anti-inflammatory function of corticosteroids. If future studies confirm these findings vitamin D may help asthma patients achieve better control of their respiratory symptoms with less medication," said Leung.
The study has been published online this week in the Journal of Allergy n Clinical Immunology.