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Prenatal vitamin D supplementation helps strengthen bones for babies born in winter

Posted on: March 9, 2016   by  Amber Tovey


As if there isn’t enough reasoning for pregnant women to supplement with vitamin D, researchers have now discovered that prenatal vitamin D supplementation benefits babies born in winter by increasing bone mass at birth.

Nutrition plays a vital role throughout life, beginning in the fetus. Therefore, researchers have conducted research to illustrate the importance of maintaining a healthy vitamin D status throughout pregnancy.

Randomized controlled trials (RCTs) are considered the gold standard of research due to their ability to prove causation. One of the most meaningful RCTs for vitamin D was conducted by Professors Carole Wagner and Bruce Hollis, along with their colleagues, in 2012. They compared maternal and birth complications between pregnant women who were administered 2000 IU of vitamin D3 daily and women who were given 4000 IU daily.

In the end, the researchers discovered that women who supplemented with 4,000 IU of vitamin D daily were more likely to have an uncomplicated birth. Whereas, women taking less vitamin D than this were more likely to have a baby born early and to develop gestational diabetes, preeclampsia or infections.

Recently, researchers conducted yet another RCT to assess whether babies born to mothers who supplemented with vitamin D during pregnancy have greater bone mass at birth than those of pregnant mothers who did not supplement. The researchers randomly assigned 569 pregnant women to placebo and 565 women to receive 1000 IU of vitamin D3 daily. All women were between 14-17 weeks pregnant and had low to normal levels of vitamin D.

Here is what the researchers found:

  • The bone mass did not differ between the infants born to mothers in the vitamin D group and the infants born to mothers in the placebo group.
  • After adjusting for season of birth in the analysis, the babies who were born in winter to mothers from the vitamin D group had greater bone mass than babies born to mothers from the placebo group (p = 0.04).
  • Women in the placebo group experienced an increased rate of severe post-partum hemorrhage than those from the vitamin D group (p = 0.01).

Why does this matter? Evidence suggests that early growth and factors in utero can affect bone mass later in life. Thus, weaker bones in infancy may predispose individuals to osteoporosis at an older age. With the rising prevalence of osteoporosis, targeting interventions early in life to improve bone mass are needed.

The researchers concluded,

“[The results] suggest the potential for beneficial effects of supplementation in pregnant women due to deliver in winter months.”

The researchers may have not found a significant effect of vitamin D supplementation on bone mass among all infants due to the relatively small dosage. Perhaps 5,000 IU daily would have made a difference in bone mass for all infants. In addition, the researchers had to exclude women with very low vitamin D levels (< 10 ng/ml), because it would be unethical to assign them to the placebo group. However, the most significant results are produced by the repletion of severely deficient individuals.

For more information about vitamin D and pregnancy, visit our page, “Vitamin D during pregnancy and breastfeeding.”


Tovey, A. & Cannell, JJ. Prenatal vitamin D supplementation helps strengthen bones for babies born in winter. The Vitamin D Council Blog & Newsletter, March, 2016.


Cooper, C. et al. Maternal gestational vitamin D supplementation and offspring bone health (MAVIDOS): a multicentre, double-blind, randomised placebo-controlled trial. Lancet Diabetes Endocrinology, 2016.

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