In a study of over one thousand children with mild to moderate asthma, children with relatively low blood levels of vitamin D were more likely to experience severe asthma attacks.
Currently, people with less than 11 nanograms (ng) per ml vitamin D in the blood are considered vitamin D deficient. Some experts believe that this value is too low and that a blood level above 30 ng/ml is required for good health. They consider a blood level of vitamin D between 11 and 30 ng/ml to be vitamin D "insufficient."
The researchers found no association between vitamin D level and protection from mild to moderate asthma attacks. The protection only extended to severe attacks.
Over the four-year course of the study, 38% of the children with insufficient vitamin D experienced an asthma attack severe enough to require a trip to the hospital. This rate was about 20% higher than that seen in children with sufficient vitamin D, 32% of whom experienced a severe asthma attack. After adjusting for age, sex, weight, income, and the initial severity of a child's asthma, this difference rose to 50%: vitamin D insufficiency made a child 50% more likely to experience an asthma attack severe enough to require a trip to the hospital.
Overall, the researchers found no association between vitamin D level and protection from mild to moderate asthma attacks. The protection only extended to severe attacks.
The study information came from a clinical trial testing two inhaled asthma medications, budesomide and nedocromil. The beneficial effect of vitamin D on asthma attacks was mainly seen in children who were using budesomide.
While vitamin D is mainly known as necessary for proper bone development, it also plays a role in nerve, muscle and immune system function. Many different studies conducted over the past decade suggest that vitamin D plays a much broader role in metabolism than was once thought. This study suggests that increased vitamin D consumption might lessen the frequency of severe asthma attacks.
An ahead-of-print version of an article detailing the asthma study was published online by the Journal of Allergy & Clinical Immunology on June 10, 2010.
It is often hard to obtain 400 IU per day of vitamin D from food alone. Fatty fish contain fairly high amounts of Vitamin D. Most of the rest of dietary vitamin D comes from fortified milk, which contains 400 IU vitamin D per quart. Certain other foods, such as orange juice and breakfast cereals, also contain some added vitamin D.
Vitamin D is also produced in the skin upon exposure to sunlight. The modern emphasis on minimizing exposure to direct sunlight coupled with the fact that little vitamin D is made by people with darker skin means that sunlight is not a significant source of vitamin D for many people in the U.S.