Women taking daily vitamin D supplements during pregnancy had children with stronger bones, with benefits lasting into mid-childhood, a new study has found.

The randomized controlled trial established a causal link, suggesting that vitamin D supplementation during pregnancy directly strengthens children’s bones.

Rebecca Moon, study investigator and clinical lecturer in child health at the University of Southampton in England, said in a statement, “This early intervention represents an important public health strategy.”

Vitamin D testing is not part of universal screenings in the United States, and prenatal vitamins do not provide enough vitamin D for many women.

Strong Bones, Strong Start

Children born to mothers who took vitamin D supplements during pregnancy had bones that were 18 percent denser, on average, than those whose mothers did not take the supplement. This difference may help reduce the risk of fractures and other bone problems later in life.

Vitamin D—the “sunshine vitamin”—is essential for bone health because it helps the body absorb calcium, which is needed to build strong bones and teeth. The baby’s skeleton forms rapidly during pregnancy, and having enough vitamin D helps support this growth.

In the new study, published in the November issue of The American Journal of Clinical Nutrition, the researchers tracked pregnant women who took 1,000 international units (IUs) of vitamin D daily from the 14th to 17th week of pregnancy until delivery and followed up with 454 children aged 6 to 7.

Vitamin D “strengthens children’s bones and reduces the risk of conditions like osteoporosis and fractures in later life,” Moon said in the statement.

The findings build on previous research showing vitamin D’s ability to regulate calcium and phosphate levels, two essential minerals for developing robust bones and teeth.

Osteoporosis, a common bone disease affecting an estimated 44 million Americans, develops when the structure and strength of the bone change.

Vitamin D’s Broader Benefits for Mothers and Children

The new research builds on previous evidence from a 2018 randomized, placebo-controlled trial known as MAVIDOS (Maternal Vitamin D Osteoporosis Study), conducted by researchers from the universities of Southampton, Oxford, and Sheffield.

The MAVIDOS study followed nearly 1,000 pregnant women, all receiving 1,000 IU of vitamin D daily between 11 and 14 weeks of pregnancy.

According to the results, vitamin D supplementation during pregnancy improved bone mineral density in children at age 4.

The MAVIDOS team also demonstrated that vitamin D supplementation could alter gene activity, aiding specific genes that regulate growth and mineralization. This helps explain why children born to mothers who took vitamin D have better bone health.

The new study also supports earlier findings from a large study in Denmark, which showed that vitamin D supplementation led to stronger bones, fewer fractures in early childhood, and reduced tooth enamel defects.

Together, these studies show the importance of ensuring adequate vitamin D intake during pregnancy to promote long-term health for both mother and child, the authors wrote. They noted that follow-up studies are necessary to determine whether these early improvements in bone health persist into adulthood.

Prenatal Vitamins Not a Reliable Source

“It is unlikely your prenatal vitamin provides enough vitamin D,” according to the American Pregnancy Association. The average prenatal vitamin contains only 400 IU of vitamin D, which is insufficient for many women, making additional supplementation necessary.

While vitamin D can also be obtained through sun exposure, fatty fish, mushrooms, and certain fortified foods such as milk and eggs, many pregnant women find it difficult to get enough vitamin D from diet and sunlight alone.

“People think that if they are in the sun daily, they have adequate vitamin D levels,” William B. Grant, director of the Sunlight, Nutrition and Health Research Center in San Francisco, told The Epoch Times. “However, vitamin D is made most efficiently only when one’s shadow is shorter than one’s height, which is not the case in winter in the United States or early morning, late afternoon.”

As a result, supplements are a crucial recommendation for achieving optimal levels during pregnancy.

Grant’s research suggests that most pregnant women should aim for 2,000 IU of vitamin D per day. A recent review he co-authored recommends this dose for the general population, but some groups may need more. African American and Hispanic women, as well as those who are very overweight or obese, may need 4,000 IU per day to achieve optimal levels.

Women need to have their vitamin D levels checked at the start of pregnancy and again after three months of supplementation to see if they are on track, according to Grant. Women should consult with health care providers to ensure they are getting the appropriate amount during pregnancy, especially if they are at risk of deficiency, he noted.

More Than Bone Health

Vitamin D’s benefits extend far beyond bone health, according to Grant, who was not involved in the study. Vitamin D plays a critical role in preventing serious pregnancy complications, including gestational diabetes, preeclampsia, and preterm delivery.

Reducing these pregnancy complications is actually the more compelling reason to supplement with vitamin D during pregnancy, Grant said in an email.

Vitamin D testing is currently not included in routine prenatal screening in the United States.

“Vitamin D testing of all pregnant women would be very useful,” Grant said.

Other research shows even more benefits: Vitamin D supplementation during pregnancy reduces the likelihood of infants developing atopic eczema in their first year. In addition, women who take extra vitamin D are more likely to have natural deliveries.

Ensuring adequate vitamin D levels during pregnancy may also help prevent conditions such as autoimmune diseases, such as multiple sclerosis and Type 1 diabetes, and neurodevelopmental disorders, such as autism spectrum disorder and attention-deficit/hyperactivity disorder, later in life.