Nearly 2,000 mothers and their babies participated in the study, which found that inadequate vitamin D is linked to poorer mental and movement skills in infants.
“This study is really going to open the door for those of us who have been advocating a stronger stance on vitamin D recommendations for pregnancy and pre-pregnancy,” says Valencia Walker, MD, a neonatologist at Mattel Children’s Hospital UCLA. She reviewed the study for WebMD. “This study helps prove that D matters, and that pregnant women should not be vitamin D deficient.”
For the study, researchers measured the vitamin D levels of pregnant women mainly during their second trimester. At 14 months, their babies underwent an approximately hour-long battery of standardized tests that measured their mental development and their psychomotor skills, or their ability to control their physical movements.
In all, 1,820 mother-infant pairs took part in the study, which is published in the journal Pediatrics.
The research team found that, for both measures, babies whose mothers had an optimal level of vitamin D scored slightly higher than babies of mothers who were D deficient.
Such a small difference in scores may not make any noticeable difference for individual babies, says researcher Eva Morales, MD, PhD, MPH, of the Centre for Research in Environmental Epidemiology in Barcelona.
But because so many women don't get enough vitamin D, those small differences may translate into a large societal impact when the number of babies at risk of poorer development is taken into consideration.
“Further studies are needed to conclude if these scores can predict future neuropsychological development later in life,” Morales says.
Majority of Women Get Inadequate Amounts of Key Vitamin
Walker says certain groups have a higher risk of missing out on adequate levels of vitamin D. Those groups include women who are overweight or obese, women from lower socioeconomic backgrounds, and women with darker skin.
Geography also plays a role. People from northern states, which don’t get much sun during wintertime, often have lower levels of vitamin D.
“Even here in L.A., where it’s often sunny, people don’t get enough sun, because of smog, because they stay indoors, or because they use a lot of sunblock,” Walker says.
How Much D Is Enough?
Access to vitamin D -- whether through sunlight, food sources, dietary supplements, or a combination -- is not the only issue. It’s not clear how much vitamin D is enough to ensure healthy development, says Morales, who adds that trials are under way to determine just that.
Walker says that prenatal vitamins taken by pregnant women often provide 400 IU (international units) of D. Regardless, there's not enough research yet to say whether supplementing with more vitamin D would help.
“This study shows a relationship, not cause and effect,” says Leonardo Pereira, MD. “Would supplements improve development? We don’t know.”
Pereira, head of maternal-fetal medicine at Oregon Health and Science University in Portland, says this study “supports a role for vitamin D in neurological development, but it is not definitive evidence that should change how we practice.”
Pereira, who was not involved in the study, does not test his pregnant patients for vitamin D deficiency. But if a patient is known to have a deficiency, he will make sure to get them up to adequate levels.
“What will this mean for pregnancy outcomes? Again, we don’t know,” he says.
Walker says that although the study will not change what doctors tell their patients, it should serve as a reminder of the importance of optimizing health and nutrition.
“Being healthy matters for your pregnancy and for how well your child does later on,” she says. “Nutrition is absolutely critical to how well children do.”