Source: The Conversation – UK
Vitamins in pregnancy are usually discussed in terms of a baby’s health at birth. But could the amount of vitamin D taken during pregnancy also influence how a child’s brain works many years later?
A recent Danish study suggests that it might. Children whose mothers received a higher dose of vitamin D during late pregnancy performed slightly better on tests of verbal and visual memory at age ten than children whose mothers received the standard dose.
The findings are intriguing, but they need to be kept in perspective. The differences were small, and the higher dose was not linked to better intelligence, attention, thinking speed, planning or working memory. The researchers also did not examine whether the memory differences affected schoolwork or daily life.
The study followed children whose mothers had taken part in a randomised trial originally designed to determine whether high-dose vitamin D supplementation during pregnancy reduced the risk of persistent wheeze and asthma in offspring. From the 24th week of pregnancy until one week after birth, one group received 2,800 international units (IU), or 70 micrograms, of vitamin D each day. The other received the standard Danish dose of 400 IU, or 10 micrograms.
Of the 623 children in the original trial, 498 returned for cognitive testing at around ten years old. After accounting for factors that might have influenced the results, the researchers found that children in the higher-dose group performed slightly better at recalling words and objects and remembering where visual patterns had appeared.
They also initially appeared better at switching between different rules or ways of solving a problem. However, that result could no longer be distinguished confidently from chance once the researchers accounted for the number of tests they had carried out.
Why the findings need caution
An important strength of the study is that the mothers were randomly assigned to receive either the higher or standard dose. This makes it less likely that differences in income, diet, health or lifestyle explain the results.
However, the original trial was designed to investigate childhood wheeze and asthma. Cognition was analysed later and was not one of the study’s original outcomes.
Researchers call this a “post-hoc secondary analysis”. Testing many possible outcomes increases the chance that some apparent differences will arise by coincidence. The two memory findings survived the researchers’ statistical checks, but the improvements were modest and need to be confirmed in trials designed specifically to study cognitive development.
The number of children who returned for testing also needs to be considered. If those who returned differed from those who did not, the findings may be less representative of the original group.
The children were tested only once, at age ten. The research cannot show when the differences appeared, whether they will continue into adolescence or whether a higher dose earlier in pregnancy would have the same effect.
A child’s vitamin D level after birth is influenced by sunlight, food and supplementation, as well as maternal factors such as breastfeeding, and maternal vitamin D status. The researchers measured blood levels at six months and six years, but two tests cannot show a child’s vitamin D exposure throughout the first decade of life. The study therefore cannot establish precisely when vitamin D might have influenced development. For example, it is unclear whether the effects were caused by vitamin D exposure during pregnancy, after birth, or by vitamin D supplements taken during childhood up to the age of ten.
Most of the mothers did not have low vitamin D levels when the trial began. Only 15% had levels below 20 nanograms per millilitre, although definitions of deficiency vary. The findings tell us more about giving extra vitamin D to women whose levels were already relatively high than about treating a clear deficiency.
The researchers found no convincing evidence that the higher dose worked differently according to the mother’s starting vitamin D level. However, the unplanned analysis, small improvements and study population mean that this study alone is unlikely to justify changing UK guidance.
Around 96% of the children who completed the follow-up were white. This limits how confidently the findings can be applied to more diverse populations or groups at greater risk of low vitamin D.
This is particularly relevant in the UK because people with darker skin generally produce less vitamin D in response to sunlight. Future trials should include participants from a wider range of ethnic backgrounds and more women with low vitamin D levels.
Should pregnant women take a higher dose?
Current NHS guidance recommends that pregnant women take 10 micrograms, equivalent to 400 IU, of vitamin D each day from early October to late March.
People who spend little time outdoors or usually cover most of their skin should take this amount throughout the year. People with black or brown skin should also consider taking vitamin D all year. A doctor may recommend a different dose when blood tests show a deficiency or there is another medical reason.
The dose used in the Danish trial was seven times the routine NHS recommendation, although it remained below the adult upper limit of 100 micrograms a day. That does not show that the higher dose offers extra benefits or suits every pregnancy.
Taking too much vitamin D over time can cause calcium to build up in the body, potentially damaging the kidneys and heart. Pregnant women should not increase their dose in the hope of improving their child’s memory without first speaking to a midwife, GP or another healthcare professional. They should also check whether vitamin D is included in more than one of the supplement they are taking.
The study offers tentative evidence that taking more vitamin D during late pregnancy may have a small effect on verbal and visual memory at age ten. Further trials should make cognition a planned outcome, test children at several ages and include a more diverse group of participants.
Until stronger evidence is available, pregnant women should follow current guidance and seek individual medical advice when deficiency is suspected.
Dr Hamid A. Merchant (@HamidMerchant) is Head of Biosciences at the University of East London and has held adjunct professorships at the Health Services Academy, Ministry of National Health Services, Regulations and Coordination, Government of Pakistan, and at Dow Life Sciences, Dow University of Health Sciences. He is also an Advisory Board Member of the Association of Pharmaceutical Sciences of Great Britain. Dr Merchant has extensive experience collaborating with and undertaking projects for the pharmaceutical industry through previous academic and professional roles and have previously worked for Abbott Laboratories Ltd before joining academia. No funding was received to commission, support, or influence the preparation of this work. Dr Merchant declares that he has no financial, personal, or professional competing interests directly related to these vaccines or to the opinions, comments, and responses presented herein. Apart from the affiliations and professional experience disclosed above, there are no other conflicts of interest to declare.
Original source: https://analysis1.mil-osi.com/2026/08/07/does-more-vitamin-d-in-pregnancy-make-children-smarter/