About a third of pregnant women in the US lack sufficient vitamin D to support healthy pregnancies − new research

Children whose mothers had higher vitamin D levels during pregnancy scored better on tests of memory, attention and problem-solving skills at ages 7 to 12 compared with those whose mothers had lower levels. That is a key finding of a new peer-reviewed study that my colleagues and I published in The American Journal of Clinical Nutrition.

While vitamin D has long been known for its role in maintaining bone health, scientists have since uncovered its importance in regulating immune function, reducing inflammation and protecting the nervous system. Now, growing evidence – including our new findings – suggest it may also support brain development beginning in the womb.

My team and I found that the link between prenatal vitamin D levels and childhood cognition was strongest among Black families, who also face higher rates of vitamin D deficiency.

This suggests that vitamin D supplementation may be a promising, low-cost strategy to support brain development while reducing racial disparities. Our study also suggested that vitamin D levels early in pregnancy may be most important for childhood cognitive development, highlighting the importance of early action by health care providers.

We analyzed more than 900 mother-child pairs across the U.S. who participated in a large national study called ECHO, short for Environmental influences on Child Health Outcomes. We measured vitamin D in the mothers’ blood during pregnancy and assessed children’s cognitive abilities using a standardized test battery. We also accounted for other important factors that shape childhood development such as the mother’s education, neighborhood conditions and the child’s age and sex.

This new study builds on our earlier findings that higher vitamin D levels during pregnancy are linked to higher IQ in early childhood and with reduced behavioral problems in middle childhood.

Collectively, these studies suggest that vitamin D plays a crucial role in brain development during pregnancy, with lasting benefits for children’s cognitive and behavioral outcomes.

Why it matters

Vitamin D deficiency is a common global problem.

In the U.S., about 42% of adults have vitamin D levels below 20 nanograms per milliliter, or ng/ml, a commonly used cutoff for deficiency. About a third of U.S. pregnant women are deficient, and the rates are even higher among Black pregnant women, with 80% found to be deficient. This racial difference is partly due to differences in skin pigmentation, as melanin pigment reduces the skin’s ability to produce vitamin D from sunlight.

Although we can get vitamin D both from sun exposure and our diets, deficiency is common because these sources don’t meet everyone’s needs. Sunlight isn’t always a reliable source, especially for people with darker skin, those living in northern climates or those who often wear sunscreen or sun-protective clothing. Natural food sources such as fatty fish, egg yolks and certain mushrooms contain some vitamin D, and fortified products such as milk and breakfast cereals help, but not everyone eats enough of these foods to maintain healthy vitamin D levels.

That’s why supplements are often necessary and are recommended in many cases by the Dietary Guidelines for Americans.

Although current guidelines recommend that pregnant women consume 600 international units, or IUs, of vitamin D daily, higher doses of at least 1,000 to 2,000 IU are often needed to correct deficiency. On average, U.S. women consume only 168 IU from food and beverages, and many prenatal vitamins provide just 400 IU. This highlights an important opportunity for clinicians to improve screening and support around vitamin D supplementation both before and during pregnancy.

If a simple, low-cost strategy such as prenatal vitamin D supplementation can help support brain development, it may yield lasting benefits for children. Long-term studies have shown that higher cognitive scores in childhood are linked to better memory and reasoning in older age, as well as longer lifespan.

What still isn’t known

While our studies have linked higher vitamin D levels in pregnancy to improved cognitive and behavioral development in children, we cannot yet prove that vitamin D is the direct cause.

Therefore, studies called randomized controlled trials – the gold standard of research – are needed to confirm these findings and determine how best to translate them into clinical practice. These studies will be essential for determining the optimal target levels for vitamin D to support brain development in pregnancy.

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