Can More Vitamin D During Pregnancy Make Children Smarter?
Vitamin D is an important nutrient during pregnancy, supporting normal bone development and overall health. But could taking more vitamin D while pregnant also influence a child’s brain development years later?
A new study from Denmark has raised that possibility. Researchers found that children whose mothers received a higher dose of vitamin D during the later stages of pregnancy performed slightly better on certain memory tests when they were around ten years old.
The results are interesting, but they do not mean that taking more vitamin D during pregnancy will make a child smarter.
The study found improvements in specific areas of memory, rather than overall intelligence or general cognitive ability. More research is needed before higher-dose vitamin D supplementation during pregnancy could be recommended for this purpose.
What did the vitamin D study find?
The research followed children whose mothers had previously participated in a randomised clinical trial.
During the original trial, women were given either the standard Danish vitamin D dose of 400 international units (IU), or 10 micrograms, per day, or a higher dose of 2,800 IU, equivalent to 70 micrograms, per day.
The supplementation began from the 24th week of pregnancy and continued until one week after delivery.
The original study was designed to investigate whether taking a higher dose of vitamin D during pregnancy could reduce the risk of persistent wheezing and asthma in children.
Years later, researchers invited the children back for cognitive testing.
Of the 623 children involved in the original study, 498 completed cognitive assessments at approximately ten years of age.
Children whose mothers had received the higher vitamin D dose performed slightly better on tests involving verbal and visual memory.
For example, they showed better ability to remember words, objects and the locations of visual patterns.
There was also an initial indication that children in the higher-dose group might perform better when switching between different rules or problem-solving strategies. However, this finding became less convincing after researchers adjusted their analysis to account for the large number of tests performed.
Does vitamin D make children smarter?
Not according to this study.
The researchers did not find convincing evidence that the higher dose of vitamin D improved children's overall intelligence.
There were also no clear improvements in several other cognitive areas, including attention, processing speed, planning, reasoning and working memory.
This distinction is important.
Memory is one part of cognitive development, but better performance on a few memory tests does not necessarily mean that a child has a higher IQ or will perform better at school.
The researchers also did not establish whether the differences in memory had any meaningful effect on the children's everyday lives, academic performance or long-term educational outcomes.
In other words, the study suggests a possible connection between higher vitamin D exposure during pregnancy and certain aspects of memory, but it does not prove that extra vitamin D produces smarter children.
Why should the findings be treated cautiously?
One of the strongest features of the research is that the mothers were randomly assigned to receive either the standard or higher vitamin D dose.
Randomised trials are valuable because they can reduce the influence of other factors that may affect children's development, such as family income, diet, health and lifestyle.
However, there are several important limitations.
First, cognitive development was not the original focus of the trial. The researchers examined cognition later as a secondary analysis. This is sometimes referred to as a post-hoc analysis.
When researchers examine many different outcomes, there is a greater possibility that some statistically significant findings could occur by chance.
The two memory findings remained significant after statistical adjustments, but the improvements were relatively small. They therefore need to be replicated in studies specifically designed to investigate vitamin D and childhood cognitive development.
Another limitation is that the children were assessed at only one point in time, around age ten.
The research cannot tell us whether the differences appeared during infancy, early childhood or later childhood. It also cannot show whether the observed differences will remain during adolescence and adulthood.
Was pregnancy definitely the important period?
Not necessarily.
Vitamin D exposure after birth can also be influenced by sunlight, diet and supplements. A child's vitamin D status may also be affected by factors relating to breastfeeding and maternal vitamin D levels.
Researchers measured vitamin D levels at certain points during childhood, but these measurements cannot capture a child's vitamin D exposure continuously over the first ten years of life.
As a result, the study cannot establish exactly when vitamin D may have influenced brain development.
It is possible that prenatal exposure played a role, but the findings cannot completely rule out the influence of vitamin D exposure during childhood.
What about vitamin D deficiency?
This is another important consideration.
Most of the mothers involved in the study did not have severely low vitamin D levels at the beginning of the trial. Only around 15% had vitamin D levels below 20 nanograms per millilitre.
Therefore, the results should not automatically be interpreted as evidence that women with vitamin D deficiency will have children with poorer memory.
The study also does not establish that treating vitamin D deficiency with high-dose supplements improves a child's cognitive development.
More research involving pregnant women with different vitamin D levels is needed.
The study population also lacked ethnic diversity. Approximately 96% of the children who completed the follow-up were white.
This matters because vitamin D production from sunlight can vary according to skin pigmentation. People with darker skin generally produce less vitamin D from sunlight than people with lighter skin.
Future research should therefore include participants from a wider range of ethnic backgrounds and more people who are at increased risk of vitamin D deficiency.
Should you take extra vitamin D during pregnancy?
For most people in the UK, the answer is to follow existing NHS advice rather than automatically taking a higher dose.
The NHS currently recommends that pregnant women take 10 micrograms, or 400 IU, of vitamin D each day from early October until the end of March.
People who spend little time outdoors, usually cover most of their skin when outside, or have black or brown skin may be advised to take vitamin D throughout the year.
Some people may need a different dose if they have been diagnosed with vitamin D deficiency or have another medical reason. This should be discussed with a healthcare professional.
The Danish study used 2,800 IU of vitamin D daily, which is seven times the routine UK recommendation.
Although this amount is below the established adult upper limit of 100 micrograms, that does not mean that everyone should take it.
Taking excessive amounts of vitamin D over a long period can increase calcium levels in the blood and potentially cause health problems, including damage to the kidneys and heart.
Pregnant women should therefore not increase their vitamin D intake simply in the hope of improving their baby's memory or intelligence.
It is also worth checking the labels of prenatal vitamins and other supplements to make sure vitamin D is not being taken from several products at the same time.
The bottom line
The Danish research provides an interesting clue about the possible relationship between vitamin D during pregnancy and children's brain development.
Children whose mothers took a higher dose of vitamin D during late pregnancy performed slightly better on some verbal and visual memory tests at around ten years old.
However, the study did not show that higher vitamin D intake makes children smarter.
There was no convincing evidence of improved overall intelligence, attention, processing speed, planning or several other cognitive abilities. The memory improvements were modest, and because cognition was assessed as a secondary outcome, the findings need to be confirmed by further research.
For now, pregnant women should follow established vitamin D guidance and speak to a GP, midwife or other qualified healthcare professional if they are concerned about deficiency or their supplement intake.
The most important message is simple: vitamin D is important during pregnancy, but more is not necessarily better.
Sources
- JAMA Network Open: Danish randomised clinical trial follow-up examining prenatal vitamin D supplementation and cognitive outcomes in children at approximately ten years of age.
- NHS: Pregnancy, vitamins and supplements, including current UK guidance on vitamin D during pregnancy.
- Scientific review: Evidence concerning vitamin D production, sunlight exposure and skin pigmentation.
Disclaimer
This article is intended for general information and educational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Pregnancy and nutritional needs vary from person to person. Do not change the dose of vitamin D or any other supplement during pregnancy without first speaking with a doctor, midwife, pharmacist or other qualified healthcare professional.