Women should be taking high-dose vitamin D supplements to reduce the chances of their child developing asthma and wheezing.
Supplementing can halve the risk, especially in women with a family history of asthma and allergy, say researchers from Brigham and Women’s Hospital.
They recommend pregnant women take up to 150mg of the vitamin every day, which is 50 percent above the current recommended level for pregnant women.
Around 40 percent of small children suffer from wheezing problems, and around 20 percent have been diagnosed with asthma by the time they reach the age of six, and many cases can be traced back to a vitamin D deficiency in the mother, the researchers say.
Women should start supplementing at high levels from the time they know they are pregnant and continue taking daily supplements throughout the pregnancy, the researchers recommend.
They reanalysed data from the VDAART (Vitamin D Antenatal Asthma Reduction Trial), which published its findings in 2017. The original data showed a 20 percent reduction in asthma rates, but the Brigham discovered it was closer to 50 percent.
And the dose needs to be higher: the VDAART group recommended 4400 IUs (110 mg), but the new analyses has upped the dose to 6600 IUs, or 150 mg. Current guidelines recommend a daily dose of no more than 100 mg for pregnant women.
Most people living in the northern hemisphere are vitamin D deficient. The vitamin, which is mainly from strong sunlight, helps boost the immune system and protects against autoimmune problems like asthma and allergies.