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Are pregnant women reaching optimal vitamin D status during peak vitamin D season?

Posted on: October 4, 2017   by  Riley Peterson & John Cannell, MD.


Much research has identified that vitamin D status is associated with the changing seasons. However, even at peak vitamin D season, are individuals reaching optimum status?

A recent study published by the International Journal of Environmental Research and Public Health discovered that although season does correlate with vitamin D status in pregnant women and cord blood, but overall, pregnant women were still vitamin D deficient.

Researchers from this study included a total of 100 pregnant women from Warsaw, Poland. Half of the women were considered the ‘winter’ group, and were due to give birth between December and February. The other half were identified as the ‘summer’ group, and were due to give birth between July and August. Blood was drawn from all participants and cord blood was drawn at birth to determine vitamin D levels. Vitamin D levels above 30 ng/ml were considered optimal for the pregnant women, and vitamin D levels above 20 ng/ml were considered optimal for newborn infants.

This is what the researchers found:

  • The winter group’s average vitamin D levels were 16.5 + 8.2 ng/mL,  and the summer group’s average vitamin D levels were 22.2 + 6.5 ng/mL (p < 0.001).
  • Only 16% of the summer group and 6% of the winter group were reached optimal vitamin D status.
  • Cord blood vitamin D levels were lower among infants born in winter compared to summer (22.7 ± 11.2 ng/mL vs. 31.3 ± 9.4 ng/mL, respectively; p < 0.0001).
  • A total of 82% of infants born in summer were considered to have optimal vitamin D status compared to 62% of the infants born in winter months.

The researchers concluded:

“During the summer season, even despite visible improvement, a large group of women still remains at risk for vitamin D deficiency.”

They continued:

“However, the conclusions about neonates are more favorable due to both, higher umbilical cord blood levels as compared to maternal concentration and a lower criterion of normal vitamin D levels for fetuses (by 10 ng/mL).”


Wierzejska, R. Vitamin D Concentration in Maternal and Umbilical Cord Blood by Season. International Journal of Environmental Research and Public Health, 2017.

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