Children with asthma are often deficient in vitamin D and more likely to suffer asthma attacks, which are typically triggered by respiratory tract infections. Researchers said that vitamin D stimulates the immune system to produce peptides, which help protect against bacteria and viruses. In one study, doctors measured vitamin D blood levels in 1,024 children with mild to moderate persistent asthma and found 35 percent had low vitamin D; less than 30 nanograms per milliliter of blood.
Children then took an asthma steroid inhalant, a non-steroidal anti-inflammatory inhalant, or a placebo. Doctors wanted to see which children would need additional medical attention and found those with good vitamin D levels were 33 percent less likely to need a hospital visit for asthma.