The researchers looked at seven studies of vitamin D’s effect on asthma involving 435 children and two studies involving 658 adults. They found that oral vitamin D reduced the risk of asthma attacks requiring hospitalization from six percent to three percent, and they also found that vitamin D reduced the likelihood of asthma attacks requiring treatment with steroids.
The studies that showed best effects were mostly the ones that involved adults with mild or moderate asthma, so the effect of vitamin D in children and in adults with severe asthma is not yet known. And it’s unclear whether vitamin D is only useful in those who are deficient in it. But because it may also help in staving off respiratory infections, it might be worthwhile to use it while further research is carried out over the coming months.