According to a study in the Journal of the American Medical Association (JAMA), vitamin D is not helpful for treating adult asthma. Study participants were given high levels of vitamin D over the course of 28 weeks. The vitamin D treatment did not improve asthma control, airway function, quality of life, or airway inflammation. Though vitamin D has not been previously associated with reducing asthma symptoms, this result is still surprising, since low vitamin D levels in asthma patients have been linked to worse symptoms and a double-blind study of Japanese children found that supplementation with vitamin D reduced the incidence of asthma attacks compared with a placebo.
Other research has suggested that adequate vitamin D is important for supporting health, including conditions affecting bone, immune function, skin, and mood.