A reanalysis of a pregnancy trial links higher vitamin D to modest improvements in children’s memory at 10, while specialists emphasise caution and adherence to existing guidance
Published: 16:00 BST, 18 May 2026 | Updated: 16:59 BST, 19 May 2026. A recent reanalysis of data from a prenatal supplement trial suggests that taking larger amounts of vitamin D during pregnancy may be associated with slightly better memory performance in children at age 10.
The investigation compared outcomes for children whose mothers received the standard UK-recommended dose with those given a substantially higher daily dose. The result was a modest advantage in some cognitive tests for the higher-dose group, prompting renewed interest in how prenatal nutrition might shape long-term neurodevelopment.
The original clinical trial randomized expectant mothers to receive either a daily 10mcg supplement — the current NHS recommendation — or a higher 70mcg dose. Follow-up assessments included approximately 500 children who completed memory testing at 10 years old. Researchers reported that, on average, children in the higher-dose group scored a little better on those memory measures.
It’s important to note that this analysis was not the trial’s pre-specified primary outcome and therefore has characteristics of an ad hoc analysis, which affects how confidently the findings can be interpreted.
Study design and what the results show
The trial underpinning this analysis was a randomized supplement study in pregnant women, with two distinct daily dosing regimens: the routine 10mcg and an experimental 70mcg. Approximately 500 children were available for cognitive testing at the 10-year mark, giving the team an opportunity to explore long-term outcomes beyond infancy. The reported differences in memory were modest rather than dramatic; children whose mothers had the higher intake performed slightly better on selected tests. Statistically significant or clinically meaningful thresholds were not broadly met across all assessments, which is why the authors and commentators urge careful interpretation.
Timing and persistence of effects
One striking aspect is that these patterns only emerged when children were assessed a decade after exposure, suggesting that any influence of maternal vitamin D may take years to appear in measurable ways. Animal research has previously hinted at links between prenatal vitamin D status and later cognitive traits, and investigators note the potential for a larger benefit in populations with poorer baseline nutrition. However, because the effect surfaces only after many years and the original trial participants generally had adequate vitamin D levels to start with, generalizing the findings to other groups requires caution.
Expert reactions and limitations
Researchers and clinicians have reacted with a mix of interest and restraint. Professor Andrew Shennan from King’s College London commented that, given the relative affordability and safety of vitamin D at these doses, a confirmed effect could have meaningful public health implications. He also emphasised that because this was an ad hoc analysis, the finding might be due to chance and should be replicated in other datasets before informing policy. The cautious endorsement highlights the potential but stops short of recommending immediate changes.
Methodological cautions
Other experts stressed the study’s limits. Lucía Iglesias Vázquez pointed out that the analysis was performed after the fact and involved modest effect sizes; many participants already had sufficient vitamin D at baseline, which limits how broadly the result can be applied. Professor Asma Khalil noted that while the findings add to evidence supporting the role of vitamin D in pregnancy, they do not justify altering clinical practice or implying that large doses will make children inherently ‘smarter.’ Both emphasised the need for replication and for trials designed with cognitive outcomes as primary endpoints.
What this means for pregnant women and public guidance
For now, health authorities continue to recommend the established regimen. The NHS advises that all pregnant and breastfeeding women take a daily 10-microgram vitamin D supplement to support maternal bone health and fetal development of bones, teeth, kidneys, heart and the nervous system. Clinicians urge women to follow current guidance and to discuss any intention to take higher doses with their healthcare provider. While the new analysis is intriguing and encourages long-term follow-up in nutritional studies, it does not replace carefully controlled trials designed to test cognitive outcomes as primary measures.
