Vitamin D is known as the “sunshine” vitamin for the body’s ability to synthesize it from exposure to sunlight. It has also been linked to just about every health condition under the sun! In addition to having numerous benefits for bone, brain, cardiovascular, immune, metabolic, and respiratory health (check out “Don’t Forget Vitamin D this Cold and Flu Season”), vitamin D is a critical nutrient for a healthy pregnancy. Emerging evidence helps us understand the precise benefits of vitamin D during pregnancy, and while this research is fairly new, the evidence of vitamin D’s benefit is strong. 

Vitamin D, pregnancy benefits, and the consequences of deficiency

Research shows that vitamin D may benefit certain complications during pregnancy. For maternal health, these complications may involve blood pressure, blood sugar balance and cesarean section (c-section). For the baby’s health, they include preterm birth^2,3, low birthweight⁴, birth length, and head circumference at birth. Despite potential complications, an estimated 33% of pregnant women in the U.S. are deficient in vitamin D¹, and some research suggests that the percentage is even higher.^1,5 Below are examples of how vitamin D may reduce the risk of pregnancy complications.

Vitamin D’s prenatal benefits for mothers:

Vitamin D and Preeclampsia

This is one of the leading causes of maternal death.⁶ It occurs in about 3-6% of pregnancies⁷, including in the postnatal period. Deficiency in vitamin D may increase the risk of this complication.^2,8–13 Yet despite this evidence, the American College of Obstetricians and Gynecologists has not found sufficient evidence to advise supplemental vitamin D3 as a nutritional intervention to prevent preeclampsia.

Vitamin D and Gestational Diabetes

Fourteen percent of pregnancies in the U.S. are impacted by blood sugar complications, and research increasingly suggests that vitamin D deficiency may play a role.^14–16 Vitamin D insufficiency may impact blood sugar balance during pregnancy. One recent study shows that blood sugar balance was more easily achieved with sufficient blood levels of vitamin D.¹⁰ Another study reported that pregnant women who supplemented with 50,000 IU of vitamin D3 once every three weeks (about 2400 IU/day) significantly improved their metabolic status, including fasting blood sugar levels, and insulin levels.¹⁷

Vitamin D and C-Section 

Nearly 32% of births in the U.S. are delivered by this alternative delivery method.¹⁸ Complications that accompany blood pressure and blood sugar imbalances increase the chances of such a delivery.^19,20 Research shows an indirect link between vitamin D and this alternative delivery method. One study showed that pregnant women with deficient vitamin D blood levels were nearly twice as likely to deliver by this method compared to pregnant women with higher vitamin D levels. Other researchers reported that this was four times more likely.^21,22 Similarly, pregnant women who took 50,000 IU every three weeks (average of about 2400 IU/day along with calcium), were three times less likely to deliver via an alternative delivery method, compared to the placebo group.²³

Vitamin D’s prenatal benefits for infants:

Vitamin D and Preterm Birth

This is one of the leading causes of infant mortality, and represents an estimated 9.6% of infants born in the U.S. Vitamin D deficiency has been linked to this pregnancy complication^24–28, with a recent study suggesting that sufficient levels of vitamin D may decrease the likelihood by 40%.¹⁰ Similarly, in another study, researchers reported 60% fewer of these births in women with higher vitamin D levels (>40 ng/mL) compared to women with lower levels.¹³ It’s important to note that vitamin D and calcium supplementation may play a role in this potential complication.¹

Vitamin D and Size at birth

Low birthweight, birth length, and head circumference at birth are linked to the pregnancy complications discussed above, and they have also been linked to vitamin D status. Research shows that higher vitamin D levels are associated with higher infant birthweight and larger head circumference.²⁹ Further, vitamin D deficiency may be associated with low birthweight, smaller head circumference, and decreased birth length.^25,30,31

Vitamin D benefits beyond pregnancy

Maternal vitamin D status during pregnancy has clear effects on fetuses as well as on newborn infants, and even on the health of the child later in life. This is why supplementation during pregnancy is so critical. Researchers have reported clear associations between vitamin D and bone, respiratory and blood sugar health. 

• Insufficient amounts of vitamin D during pregnancy have been linked to a reduction in bone mass in infants that can persist for at least nine years after birth.^32–34
• Respiratory health in newborns to 3-year-olds have also been linked to maternal vitamin D intake during pregnancy.³⁵
• Researchers reported that in a cohort of ~30,000 pregnant women, children born to women with prenatal vitamin D levels of <54 nmol/L (21.6 ng/mL) were twice as likely to have blood sugar imbalance than children born to women with prenatal vitamin D levels of >89 nmol/L (35.6 ng/mL).³⁶

Although health complications from lack of vitamin D are a concern for both mom and baby, the good news is that it helps to simply include this vital nutrient in the diet. 

How much vitamin D should you get during pregnancy?

In short, it depends, but according to the Endocrine Society Clinical Practice Guidelines without proper sun exposure vitamin D supplementation is needed in order to get adequate amounts.⁵ Getting your vitamin D levels tested to determine if you are getting enough is ideal. Vitamin D testing requires a simple blood test that can be requested through your doctor. Outside of testing, there are standard guidelines that can help direct you to appropriate vitamin D supplementation which is based on clinical research and takes into consideration factors that increase the risks of vitamin D deficiency. 

Factors that contribute to vitamin D deficiency

Historically, most people relied on sun exposure to produce vitamin D.³⁷ However, due to modern indoor living and increased knowledge of the risks of skin cancers, for most, the limited sun exposure can limit vitamin D production.  Factors that contribute to vitamin D deficiency during pregnancy are mainly due to lack of direct sun exposure (for various reasons), lack of vitamin D in the diet (without supplementation), or genetic factors that limit the amount of vitamin D produced by the body.

Some major factors that increase the risk of vitamin D deficiency include limited sun exposure due to indoor working environments, sunscreen use, dietary choices, inadequate vitamin D3 supplementation, geographical location, time of year, darker skin pigmentation, etc.^38–41 For more information about vitamin D, refer to “An Introduction to Vitamin D”.

Recommended amounts of vitamin D

Typically, you don’t want to take too little or too much of anything during pregnancy. Recent research shows that taking enough vitamin D during pregnancy is very important, and that many pregnant women should take more depending on their risk of vitamin D deficiency. Below are some recommendations for vitamin D intake during pregnancy and lactation. Also included are amounts suggested by vitamin D clinicians and researchers based on clinical observation.⁴² Generally speaking, higher vitamin D intakes appear more effective and remain safe.

*For women ages 19-50 years; **For lactation 4000-6000 IU/day is mother’s required intake if infant is not receiving 400 IU/day.

[Table is modified from Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline https://www.ncbi.nlm.nih.gov/pubmed/21646368].

These values may seem high to some, but research strongly suggests that more vitamin D is needed than has been previously thought.

• Researchers report that even when pregnant women are taking 600 IU/day of vitamin D3 as part of their prenatal supplement, plus consuming two glasses of milk, 76% of moms and 81% of newborn babies were deficient in vitamin D, with levels of less than 20 ng/mL.⁵
• A similar result is seen when pregnant women take 400 IU vitamin D3 as part of their prenatal vitamins, as this amount may not be enough to obtain sufficient blood levels.⁴³
• Another study showed that when comparing doses of 400, 2000, and 4000 IU/ day from early pregnancy (12–16 weeks) to delivery, 4000 IU was the most effective at safely increasing vitamin D blood levels—no adverse events were reported in any group.⁴⁴

Interest in the impact of vitamin D during pregnancy is growing, and the evidence of its benefit is strong. Research shows that sufficient vitamin D levels can help support a healthy pregnancy. Taken together these studies suggest that it’s important to consider the factors that increase risks of vitamin D deficiency, get vitamin D levels tested when possible, and then adjust vitamin D intake accordingly. Supplementation of vitamin D3 is vital for most pregnant women and it’s likely more than what’s in a standard prenatal vitamin.