New Study Suggests Higher Vitamin D Doses During Pregnancy May Aid Child Memory

Women who are pregnant are routinely advised to take prenatal vitamins for their health and fetal development.

A new study published in JAMA Network Open on Monday found that children whose mothers took higher doses of Vitamin D supplements during pregnancy performed better on some memory tests by the age of 10.

But what exactly did the study find? How significant are these differences? Should pregnant women start taking higher doses of Vitamin D? What do experts say about the risks of taking too much?

CNN spoke with health and wellness expert Dr. Liana Wen, an emergency physician and associate professor at George Washington University School of Medicine. She is also a former Baltimore City Health Commissioner.

CNN: What is the takeaway from this new study about Vitamin D supplements during pregnancy and children's cognition?

Dr. Liana Wen: This study is a randomized clinical trial conducted in Denmark that followed about 500 children until they were 10 years old. Researchers studied whether taking higher doses of Vitamin D3 during pregnancy was associated with improved cognitive performance later in childhood.

The trial involved hundreds of women who were randomly assigned during pregnancy to receive either a high dose of Vitamin D3 or a standard dose. The high-dose group received an additional 2,400 international units (IUs) daily on top of the usual amount in prenatal vitamins, while the other group received the recommended dose of 400 IUs daily.

When the children reached age 10, the offspring of mothers who participated in the Vitamin D3 trial underwent a series of neurocognitive tests. Researchers found that children in the higher-dose group performed slightly better on some measures of verbal memory, visual memory, and cognitive flexibility, which is the ability to switch attention or adapt to changing tasks. However, the study did not find significant differences in overall IQ scores.

The recorded improvements were statistically significant but limited. These findings suggest a potential for subtle effects of prenatal Vitamin D exposure on certain aspects of brain development, but they do not mean that high doses of the vitamin during pregnancy significantly boost intelligence or academic performance.

CNN: What distinguishes it from previous research on Vitamin D and brain development?

Dr. Liana Wen: One of the strongest points of this study is that it was a randomized controlled clinical trial. Participants did not know which group they were in at the start, which is important because many previous studies on Vitamin D and neurodevelopment have been observational, meaning they can spot associations but cannot prove cause and effect, due to many other factors that could explain the results.

Participants were randomly assigned to different doses of Vitamin D during pregnancy, which helped reduce bias and confounding factors. Researchers also followed the children for a long period, as many previous studies focused on developmental outcomes in infancy or early childhood, while this trial studied cognition at age 10, a stage where more advanced cognitive functions like memory and executive functions can be tested.

Another notable finding was that the study did not find a clear effect associated solely with the mother's blood Vitamin D levels. In other words, there was no specific level of the vitamin after which children's outcomes clearly started to improve. A commentary accompanying the study noted that Vitamin D may function more like an "evolutionary signaling molecule," meaning its effects are complex and not tied to a single precise threshold for benefit.

CNN: Researchers found benefits in some memory tests, but not in general intelligence. How do you interpret these findings?

Dr. Liana Wen: I think it's important here to clarify what the study showed and what it did not show. The study did not prove that Vitamin D supplements make children generally smarter, as there were no differences in IQ scores or overall cognitive indicators.

She added that the improvements appeared in more specific areas, particularly some aspects of memory. The commentary accompanying the study explained that this pattern might be biologically plausible, especially since Vitamin D receptors are present in areas of the brain associated with memory and executive functions.

However, these differences were relatively small, and the results should not lead to broad conclusions or major changes in behavior, but rather are part of a wider scientific discussion about the impact of nutrition during pregnancy on long-term child development.

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

Dr. Liana Wen: According to the American College of Obstetricians and Gynecologists, routine screening for Vitamin D deficiency during pregnancy is not recommended for all women. However, screening may be considered for pregnant women who are at higher risk of deficiency, including those with limited sun exposure, those with darker skin, or those with gastrointestinal disorders or obesity.

Most prenatal vitamins contain Vitamin D, usually at a dose of around 400 IUs daily. Recommendations suggest that when Vitamin D deficiency is diagnosed during pregnancy, supplementation at a dose of 1,000 to 2,000 IUs daily is generally considered safe.

However, the dose used in this study was much higher than the usual doses in pregnancy supplements, explaining that this "does not mean that it is dangerous, but that pregnant women should not automatically start taking higher doses on their own."

CNN: Can excessive Vitamin D be harmful during pregnancy?

Dr. Liana Wen: Yes. Especially since Vitamin D is fat-soluble. Excess amounts can build up in the body, and very high levels of the vitamin can lead to high blood calcium, which can cause nausea, vomiting, kidney stones, and kidney damage. In severe cases, high calcium can affect the heart and other organs.

Pregnancy often involves taking many supplements at once, and a woman may already be getting Vitamin D from her prenatal vitamins and then add other high-dose supplements without realizing the total amount she is taking. For this reason, I strongly caution against taking large doses without medical supervision. Nutritional interventions during pregnancy should be individualized and discussed with an obstetrician-gynecologist.

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

Dr. Liana Wen: Again, I do not recommend it based on this study alone. The results are interesting and may be important, but the cognitive differences observed were limited.

I believe the study raises important scientific questions and may contribute to a future re-evaluation of current recommendations. However, we are not yet at a stage where medical organizations advise all pregnant women to routinely take high doses of Vitamin D.

In my opinion, it is most appropriate for pregnant women to discuss their individual circumstances with their obstetrician-gynecologist. A woman who has a Vitamin D deficiency or is at higher risk for it may benefit from supplementation, but this decision should be made carefully and as part of comprehensive prenatal care.

CNN: What are the most important things pregnant women can do to support their children's long-term health and development?

Dr. Liana Wen: One of the most important things is to focus on the basics that we already know help improve maternal and child health. These steps include getting regular prenatal care, taking prenatal vitamins as recommended, eating a balanced diet, avoiding smoking and alcohol, managing chronic conditions, and staying physically active.

Sleep and mental health are also very important and often overlooked, even though chronic stress, untreated depression, and lack of sleep can all affect maternal health and pregnancy outcomes. Nutrition during pregnancy is important, but factors after birth also play a role, including having a stable home environment, early learning opportunities, sleep, nutrition, and emotional support.

It is important for pregnant women to remember that a child's healthy development is influenced by many factors that extend over many years.