Q. Will taking vitamin D prevent or improve my asthma symptoms?
A. High-quality evidence suggests that taking vitamin D along with standard asthma medication can reduce the number of severe asthma exacerbations.
However, it does not appear to improve lung function or day-to-day asthma symptoms. The findings were published in September 2016 in the Cochrane Database of Systematic Reviews.
Researchers looked at nine randomized controlled trials—two involved 658 adults and seven involved 435 children. Most people continued to take their usual asthma medication while participating in the studies, which lasted for four to 12 months.
Use of an oral vitamin D supplement cut the risk of severe asthma attacks requiring hospitalization or an emergency department from 6 percent to around 3 percent. Use of a vitamin D supplement also reduced the rate of asthma attacks requiring an oral steroid.
Keep in mind that the findings relating to severe asthma attacks come from just three of the nine trials. And most of those study participants were adults with mild or moderate asthma.
Further studies are needed to learn whether people with severe asthma will also benefit. Another question: Is vitamin D beneficial for all asthma patients or just those with low vitamin D levels?
In the meantime, adequate vitamin D consumption is important for your overall health. The recommended dietary allowance for healthy adults is 600 international units (IU) per day. Your doctor can perform a simple blood test to determine if you are vitamin-D deficient and need a higher dose.