Taking Vitamin D supplements in addition to asthma medication appears to cut the risk of severe asthma attacks, a review of evidence suggests. An independent review by the Cochrane research body of nine clinical trials found it also cut the rate of asthma attacks needing steroid treatment. But researchers say it is unclear whether it only helps patients who are vitamin D deficient. They say more studies are needed before they can give patients official advice. They recommend talking to a GP or pharmacist to get advice before taking a vitamin D supplement. The Cochrane review’s lead author, Professor Adrian Martineau, said they found vitamin D “significantly reduced the risk of severe asthma attacks, without causing side effects”. They found taking vitamin D reduced the risk of severe asthma attacks requiring a hospital admission or a visit to A&E from 6% to 3%. They also found the rate of asthma attacks needing steroid treatment dropped from 0.44 to 0.28 attacks per person per year.