Lack of Vitamin D May Aggravate Asthma

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.

About 35% of the children in the trial had vitamin D insufficiency.

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.

There is controversy over what the recommended daily intake of vitamin D should be. The Institute of Medicine recommends 200 International Units (IU) per day for people aged 14-50, 400 IU/day at ages 51-70, and 600 IU/day for people over 70. These values were established in 1997 and since that time, many studies have suggested that they may be too low. A committee was set up to re-evaluate these values in 2008 and is expected to offer its report later this year. In the meantime, the American Academy of Pediatrics recommends that children and adolescents who drink less than a quart of fortified milk daily should take a 400 IU vitamin D supplement daily. Breastfed infants or any infants who do not consume at least one liter of vitamin D fortified formula daily should also take a 400 IU vitamin D supplement daily.

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.