How Does Lack of Vitamin D During Pregnancy Affect a Child?

Some evidence suggests a lack of vitamin D can affect a child’s mental health, but the number of children affected is small. Here's what you should know.

If you are pregnant, your doctor probably told you to take folic acid. You might also ask to be checked for adequate vitamin D and consider taking supplements for the sake of your child’s mental health.

A child born with low blood levels of vitamin D is 33 percent more likely to develop autism spectrum disorder (ASD), compared to infants on the other side of the range, according to results described at the 2018 International Society for Autism Research annual meeting in Rotterdam, the Netherlands.

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The results came from almost 3,400 infants born in Sweden between 1996 and 2000, including nearly 1,400 who later got an ASD diagnosis.

In a 2019 study of mothers and children in Spain, researchers found the more vitamin D in a mother’s blood during pregnancy, the better her child did on a test of social skills five years later. This team didn’t see an impact on the children’s behavior past that age.

In a larger, 2017 study of more than 4,000 children in the Netherlands, they were twice as likely to have an autism diagnosis by the age of six if their mother was short of vitamin D while pregnant. Only 68 of the children had an ASD diagnosis, however. As lead researcher John McGrath, professor at Aarhus University in Denmark and the Queensland Brain Institute in Australia, pointed out, “Mothers with vitamin D deficiency during pregnancy need not panic about the mental health of their children.”

We get vitamin D mainly from sunlight, although oily fish and fortified margarines, eggs, and milk provide some of the vitamin. In 2008, a psychiatrist noticed that ASD rates went up around the time more women were worrying about sun damage and wearing sunscreen. A study of 800,000 children in Scotland concluded that ASD was more likely among children conceived in the winter, when Scotland is a dark place. Researchers calculated that a winter conception explained 11.4 percent of cases of ASD and other kinds of mental disability or learning difficulties like dyslexia.

Some people with ASD have low levels of vitamin D5, but it’s not clear when the deficiency began.

In both northern and southern latitudes many women are deficient in vitamin D, both before and during pregnancy. Using sunscreen, having dark skin, or covering yourself up with clothing all are factors. Deficiencies are more common for dark-skinned people who live far from the equator.

Lack of vitamin D in the womb would need to combine with other factors. After all, children with ASD are born to mothers who don’t have vitamin D deficiency, and not all children born to mothers who do end up having ASD. There may be a key window — somewhere mid-way in a pregnancy — when adequate vitamin D is most required for normal brain development. Vitamin D affects almost all areas of the central nervous system, and it controls the way brain cells develop and some brain chemicals express themselves.

Since nutrients often come together, it could be that another nutrient linked to vitamin D is significant. We also don’t know what effect supplements might have. To be sure, we’d need to analyze ASD rates among children born to mothers who took vitamin D supplements to see if they were lower than in a control group.

Talk to you doctor if you think supplements could help you.

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