Two new trials have found no significant statistical reduction in cases of persistent wheezing and asthma where the mother had taken additional vitamin D supplements during pregnancy. For one of the trials, conducted by researchers at the University of Copenhagen, two groups were assigned either daily vitamin D (2,400 IU/day; n=315) or a placebo (n=308) from pregnancy Week 24 to 1 week postpartum. This was in addition to 400 IU/day of vitamin D3, which was a part of their usual pregnancy regimen.

Upon follow-up at the children turning age 3, no significant reduction of persistent wheezes in the supplemental vitamin D group was evident. Cases of persistent wheezing were diagnosed in 47 children (16%) in the regular vitamin D group and 57 children (20%) in the control group. Although there was no difference in persistent wheezing, the authors did note a reduction in the number of episodes of troublesome lung symptoms. Authors suggest that further studies be conducted using a larger sample size and earlier treatment intervention to test the effects of vitamin D supplementation and wheezing reductions.

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In a separate trial, doctors at Brigham and Women’s Hospital in Boston randomized 881 pregnant women at f 10 to 18 weeks’ gestation. The women in this study were also considered to be at ‘high risk’ of having children with asthma. They were assigned 4,000 IU vitamin D plus a prenatal vitamin containing 400 IU vitamin D (n=440), or a placebo plus a prenatal vitamin containing 400 IU vitamin D (n=436).

Again, an analysis was conducted after 3 years. Of the 806 children who were still part of the study, 218 were diagnosed with asthma or recurrent wheeze; 98 of 405 (24%) in the 4,400-IU group and 120 of 401 (30%) in the 400 IU group. The absolute difference of 6% between both groups was not statistically significant regarding efficacy of vitamin D supplementation.

The conclusion of the two separate studies was similar; both authors called for further studies that contained larger samples to be conducted. And while the results did not show significant reduction inrates of respiratory problems, the authors speculate that the inexpensive intervention of vitamin D supplementation could be substantial.  

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