Children with severe therapy-resistant asthma may have worse symptoms due to lower levels of vitamin D in their blood, researchers in London say. Dr. Atul Gupta, a researcher at Royal Brompton Hospital and the National Heart and Lung Institute at Imperial College and King\'s College London, said lower levels of vitamin D may cause structural changes in the airway muscles of children with severe asthma. While most children with asthma can be successfully treated with low doses of corticosteroids, about 5 percent to 10 percent do not respond to standard treatment, Gupta said. Those with severe therapy-resistant asthma, experience more asthma episodes and asthma-related illnesses, and require more healthcare services, than their treatment-receptive peers, Gupta said. \"This study clearly demonstrates that low levels of vitamin D are associated with poorer lung function, increased use of medication, worse symptoms and an increase in the mass of airway smooth muscle in children with severe therapy-resistant asthma,\" Gupta said in a statement. \"It is therefore plausible that the link between airway smooth muscle mass and lung function in severe asthma may be partly explained by low levels of vitamin D.\" The findings are published in the Journal of Respiratory and Critical Care Medicine.