Vitamin D reduced the risk of emergency department visits or hospitalisation for asthma from 6% to 3% over six to twelve months, and also reduced the risk of less serious asthma attacks from 29% to 18%. These results are illustrated in the Cates plots shown below:
People with an asthma attacks leading to ED visit or hospitalisation
In the control group 6 out of 100 people had a visit to ED or hospitalisation over 8 months, compared to 3 (95% CI 1 to 5) out of 100 on vitamin D (mostly evidence from trials on 658 adults).
People with one or more asthma attacks (as defined in each trial)
In the control group 29 out of 100 people had a study-defined exacerbation over 7 months, compared to 18 (95% CI 10 to 29) out of 100 on Vitamin D (from trials in 658 adults and 341 children).
For full details of the review please follow this link. The evidence from children is still rather limited and we do not know for sure what dose of Vitamin D is needed or what blood level of Vitamin D determines whether people benefit. Vitamin D is not a substitute for normal preventer treatment.