Higher vitamin D intake in pregnancy linked to some cognitive benefits in children

By Katia Hetter, CNN

(CNN) — Pregnant women are routinely advised to take prenatal vitamins for their health and their baby’s development. Now, a new study published Monday in JAMA Network Open concluded that children whose mothers received higher-dose vitamin D supplements during pregnancy performed better on certain memory tests at age 10.

What exactly did the study find? How meaningful were the differences? Should pregnant women start taking higher doses of vitamin D? And what do experts say are the risks of taking too much?

To help us with these questions, I spoke with CNN wellness expert Dr. Leana Wen, an emergency physician and adjunct associate professor at George Washington University. She previously served as Baltimore’s health commissioner.

CNN: What did this new study find about vitamin D supplementation during pregnancy and children’s cognition?

Dr. Leana Wen: This study was a randomized clinical trial conducted in Denmark that followed nearly 500 children until age 10. Researchers examined whether higher-dose vitamin D3 supplementation during pregnancy was associated with cognitive performance later in childhood.

The trial included hundreds of women who were randomly assigned during pregnancy to receive either a higher dose of vitamin D3 or a standard-dose supplement. The higher-dose group received 2,400 international units daily in addition to the standard prenatal amount, while the comparison group received the standard recommended dose of 400 international units daily.

At age 10, the children whose moms participated in the vitamin D3 trial underwent a series of neurocognitive tests. The researchers found that children in the higher-dose group performed modestly better on certain measures of verbal memory, visual memory and cognitive flexibility, which refers to the ability to shift attention or adapt to changing tasks. However, there were no significant differences in overall intelligence scores.

The improvements seen were statistically significant but modest. This research suggests there may be subtle effects of prenatal vitamin D exposure on certain aspects of brain development, but it does not mean that higher-dose vitamin D during pregnancy dramatically boosts intelligence or academic performance.

CNN: How was this study conducted, and what makes it different from prior research on vitamin D and brain development?

Wen: One major strength is that this was a randomized controlled clinical trial. Participants were initially blinded, meaning that they did not know which group they were assigned to. That matters because many prior studies on vitamin D and neurodevelopment have been observational, meaning they can identify associations but not cause and effect because many other factors could explain the findings.

In this study, participants were randomly assigned to different vitamin D doses during pregnancy, which helps reduce bias and confounding factors. The researchers also followed the children for a long time. Many earlier studies examined developmental outcomes in infancy or early childhood, whereas this study looked at cognition at age 10, when testing for more advanced cognitive functions such as memory and executive functioning can be conducted.

One notable finding is that the study did not find a clear threshold effect based on maternal vitamin D blood levels alone. In other words, there was not a specific vitamin D level above which children clearly performed better. That was a key point raised in an accompanying commentary, which argued that vitamin D may function more like a developmental signaling molecule whose effects are complex rather than something with one precise cutoff for benefit.

CNN: The researchers found benefits in certain memory tests but not in overall intelligence. How should people interpret those findings?

Wen: I think this is where clear communication of what the study shows and doesn’t show is important. The study did not show that vitamin D supplementation makes children broadly “smarter.” There were no differences in overall IQ scores or global intelligence measures.

Instead, the improvements were seen in more specific domains, particularly certain aspects of memory. The commentary accompanying the study pointed out that this pattern may actually make biological sense because vitamin D receptors are found in areas of the brain involved in memory and executive functioning.

At the same time, these differences were relatively small. This finding should not prompt sweeping conclusions or dramatic changes in behavior. It is one piece of evidence that contributes to a broader scientific discussion about how nutrition during pregnancy may affect long-term child development.

CNN: What are the current recommendations for vitamin D during pregnancy?

Wen: According to the American College of Obstetricians and Gynecologists, routine screening for vitamin D deficiency during pregnancy is not recommended for everyone. However, testing may be considered for pregnant individuals at increased risk of deficiency, including those people with limited sun exposure, darker skin pigmentation, certain gastrointestinal disorders or obesity.

Most prenatal vitamins already contain vitamin D, typically around 400 international units daily. ACOG’s recommendations state that when vitamin D deficiency is identified during pregnancy, supplementation of 1,000 to 2,000 international units daily is generally considered safe.

We should note that the dose used in this study was substantially higher than standard prenatal supplementation. That does not mean it is problematic, but it also does not mean pregnant women should automatically start taking higher doses on their own.

CNN: Can too much vitamin D be harmful during pregnancy?

Wen: Yes. Because vitamin D is fat-soluble, excessive amounts can accumulate in the body. Very high vitamin D levels can lead to elevated calcium levels, which may cause nausea, vomiting, kidney stones and kidney damage. In severe cases, excess calcium can affect the heart and other organs.

Pregnancy is also a period when people are often taking multiple supplements simultaneously. Someone may already be getting vitamin D through a prenatal vitamin and then take additional high-dose supplements without realizing how much they are consuming overall.

This is why I would strongly caution against self-prescribing large doses.
Nutritional interventions during pregnancy should be individualized and discussed with your obstetrician.

CNN: Should pregnant women start taking high-dose vitamin D supplements based on these findings?

Wen: Again, I would not make that recommendation based on this study alone. The findings are interesting and potentially important, but the cognitive differences observed were modest.

I do think the study raises important scientific questions and may eventually contribute to reassessment of recommendations. But we are not at the point where professional organizations are advising all pregnant women to take high-dose vitamin D supplements routinely.

For now, I think the appropriate message is that pregnant women should discuss their individual circumstances with their obstetrician. Someone who is deficient in vitamin D or at high risk for deficiency may benefit from supplementation, but that decision should be made thoughtfully and in the context of overall prenatal care.

CNN: Beyond vitamin D, what are the most important things pregnant women can do to support their baby’s long-term health and development?

Wen: One of the most important things is to focus on the fundamentals that we already know improve maternal and child health outcomes. Those steps include obtaining regular prenatal care, taking a prenatal vitamin as recommended, eating a balanced diet, avoiding tobacco and alcohol, managing chronic medical conditions and maintaining physical activity. Sleep and mental health are also extremely important and sometimes overlooked. Chronic stress, untreated depression and inadequate sleep can affect both maternal well-being and pregnancy outcomes.

It’s also important for pregnant women to remember that healthy child development is influenced by many factors over many years. Nutrition during pregnancy matters, but so do factors after birth, including a stable home environment, early learning opportunities, sleep, nutrition and emotional support. There is rarely one single nutrient or intervention that determines a child’s future cognitive outcomes on its own.

The-CNN-Wire
™ & © 2026 Cable News Network, Inc., a Warner Bros. Discovery Company. All rights reserved.