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Taking Vitamin D While Pregnant May Not Lower Baby's Risk of Asthma

New studies show vitamin D does not lower the odds for asthma in babies, contrary to previous belief.

Vitamin D bottle Karen Desjardin/Getty Images
We've previously been told that taking a daily vitamin D supplement during pregnancy may lower the odds for asthma in babies. But now two new studies say that's not the case.

It's been speculated that Vitamin D deficiency during pregnancy may affect immune system development in the fetus, leading to an increased risk of asthma in childhood. So in order to try to clarify a link, Dr. Hans Bisgaard led a study that tracked outcomes for more than 600 pregnant women and their children, who were then followed until 3 years of age.

Bisgaard and his team found that taking vitamin D supplements during pregnancy did not reduce the children's risk of asthma, chronic wheezing, upper and lower respiratory tract infections, or the autoimmune skin disorder eczema. But the researchers said further studies—with more participants, a higher vitamin D dose, and beginning earlier in pregnancy—may be required to reach a final conclusion

The second study involved close to 900 pregnant women at high risk of having children with asthma. Beginning at 10 to 18 weeks, the women took either 4,000 IU of vitamin D plus a prenatal multivitamin containing 400 IU of vitamin D, or a placebo plus the same prenatal vitamin. According to the researchers, by age 3, 24 percent of the children in the 4,400-IU group and 30 percent of those in the 400-IU group developed asthma or chronic wheezing

That 6 percent difference, experts said, is not statistically significant. But while there's no apparent benefit to using vitamin D supplementation for reduction of asthma, there doesn't seem to be any harm in taking it if you're pregnant either.

"Certainly the benefit of vitamin D to bone growth in the fetus is understood," Dr. Len Horovitz, a pulmonary specialist at Lenox Hill Hospital, told Health Day. "And we know that vitamin D helps the immune system and wound healing."

"So what should our current recommendations be?" postulated Dr. Alan Mensch, chief of pulmonary medicine at Northwell Health's Plainview Hospital. He told Health Day that "larger and modified studies are required before firm recommendations can be made for pregnant women."

Hollee Actman Becker is a freelance writer, blogger, and a mom. Check out her website holleeactmanbecker.com for more, and follow her on Twitter at @holleewoodworld.