What a new randomized trial says about vitamin D in pregnancy and children's cognition at age 10

Prenatal vitamins are one of the few areas of medicine where almost everyone agrees something is worth taking, and almost no one agrees on how much. A new analysis just out in JAMA Network Open weighs in on one specific question: when pregnant women take a higher dose of vitamin D than the standard prenatal recommendation, can you measure a difference in their children a decade later? The answer the researchers reached is qualified, and the qualifications matter.

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What the research found

The study is a post hoc secondary analysis of a Danish randomized controlled trial called the Copenhagen Prospective Studies on Asthma in Childhood (COPSAC2010). Between 2009 and 2010, the trial enrolled 700 pregnant women and randomized 623 of them to take either 2,800 IU per day of vitamin D3 (the high-dose arm) or 400 IU per day (the standard-dose arm), starting at pregnancy week 24 and continuing through one week postpartum.

Years later, the team brought 498 of those children back at age 10 for a comprehensive neuropsychological test battery covering 11 cognitive functions. Children whose mothers had been in the high-dose arm scored modestly higher on verbal memory (0.17 standard deviations higher), visual memory (0.24 SD higher), and a measure of cognitive flexibility (0.19 SD higher). The cognitive flexibility result did not survive correction for multiple statistical comparisons. The two memory results did.

A few things to hold steady. This was a secondary analysis of a trial originally designed to study asthma. Effect sizes were small. The cohort was almost entirely Danish, where vitamin D status differs from sunnier latitudes. And both arms received vitamin D. The comparison is high-dose versus standard-dose, not supplement versus nothing. So the takeaway is not "vitamin D is essential," which we already knew. The takeaway is that within the range tested, more was modestly better for two cognitive domains a decade later.

The bigger picture

This is not the first paper to ask the question. According to PubMed-indexed work, dozens of cohort studies have looked at maternal vitamin D status and child neurodevelopmental outcomes, with mixed results.

A 2026 randomized trial out of Finland, also recently published, tested higher-dose versus standard-dose vitamin D in infants from birth to age 2 and looked at autism-related traits at ages 6 to 8. The headline finding was that higher supplementation did not change autism trait scores overall. A sex-stratified analysis suggested an association in boys, but the headline was negative for the full sample.

So the field, taken together, looks like this. Vitamin D is plausibly involved in brain development. Frank vitamin D deficiency in pregnancy is bad for many reasons, cognitive development among them. Whether pushing dose above current recommendations buys you measurable cognitive gain is still being worked out, and the answer probably depends on the woman's baseline status, her genetics, and the outcome being measured.

The dose used in the new Danish study, 2,800 IU per day, is higher than the 400 to 600 IU in most prenatal vitamins but well below thresholds linked to toxicity. The American College of Obstetricians and Gynecologists currently recommends 600 IU per day in pregnancy, with higher doses considered case-by-case when a woman is documented deficient.

The naturopathic lens

In clinic I see two opposite mistakes around vitamin D in pregnancy. The first is treating it like a multivitamin afterthought, with no testing and no thought beyond what the prenatal contains. The second is reaching for very large doses based on online recommendations without any blood level to anchor the choice.

What the new study supports, in my read, is the middle position. Vitamin D is a real signal in fetal brain development, not a wellness add-on. Worth measuring before pregnancy if possible, worth measuring early in pregnancy if not. Dose decisions belong in the conversation between a pregnant woman and her prescribing provider, with actual blood levels (25-hydroxyvitamin D) guiding the conversation rather than blanket recommendations.

The other thread I find interesting is what the supplement is not a substitute for. Pregnant patients who are vitamin D deficient often have other patterns alongside it: sparse sunlight, low fish intake, gut absorption issues, dark skin without adjusted supplementation guidance, or stress patterns that erode many micronutrients in parallel. Treating only the D number while ignoring the surrounding picture misses the point. Naturopathic care for pregnancy tries to look at the whole picture: micronutrient status, sleep, blood sugar, stress, gut health, thyroid, and the relational support a woman has around her.

How to apply this now

1. If you are pregnant or planning pregnancy, ask your provider for a 25-hydroxyvitamin D blood test. Many providers will test on request even if it is not routine.

2. Do not self-prescribe high-dose vitamin D in pregnancy based on a single study. The Danish trial used 2,800 IU per day under medical supervision. Dose decisions should account for your baseline level, your weight, your skin tone, your latitude, and your prenatal vitamin's existing content.

3. Look at the rest of the picture. Sun exposure when safe, fatty fish a couple of times a week if tolerated and clean, eggs, mushrooms exposed to UV light, and fortified foods all contribute. Supplements are one input among several.

4. If your prenatal vitamin contains only 400 IU of vitamin D, that is the floor, not necessarily the right number for you. Talk to your provider before adjusting.

A small but real cognitive signal in 10-year-olds, traced back to a maternal supplement choice in the third trimester, is exactly the kind of finding that earns its place in the pregnancy conversation without overpromising. It is not a guarantee. It is one more reason to pay attention.

References

1. Frederiksen OF, Jepsen JRM, Brustad N, et al. High-dose vitamin D3 supplementation during pregnancy and test-based cognitive performance at age 10 years: a post hoc secondary analysis of a randomized clinical trial. JAMA Netw Open. 2026;9(5):e2611464. PMID: 42149595. doi:10.1001/jamanetworkopen.2026.11464.

2. Sandboge S, Seppälä V, Lintula S, et al. Vitamin D supplementation in the first 2 years and autism spectrum traits at 6-8 years - a randomized clinical trial. J Child Psychol Psychiatry. 2026;67(7):1004-1014. PMID: 41486975. doi:10.1111/jcpp.70110.

Disclaimer

This article is for educational purposes only. It is not medical advice, does not create a clinician-patient relationship, and is not a substitute for individualized prenatal care. Do not start, stop, or change any supplement, especially in pregnancy, based on what you read here. Pregnancy care belongs with a qualified prenatal provider who knows your full medical history.

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