Pregnancy The Science of Nutrition

How Risky Is Vitamin D Deficiency in Pregnancy?

Hillary Bennetts

How Risky Is Vitamin D Deficiency in Pregnancy?

Table of contents

  • Intro
  • Why Vitamin D is Needed
  • The Risks of Deficiency
  • Risks to Pregnancy Outcomes
  • Risks to Baby’s Short- and Long-Term Health
  • Prevalence of Deficiency
  • How Much Do You Need?
  • Types of Vitamin D
  • Sources of Vitamin D
  • The Bottom Line

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You might have noticed that there has been a lot of talk about Vitamin D lately. Thanks to its immune boosting benefits and research linking adequate Vitamin D levels to more mild COVID cases, Vitamin D is finally starting to get the spotlight it deserves. 

We want to shine that same spotlight on Vitamin D in pregnancy, because research shows that the risks of deficiency during pregnancy have long lasting effects on mama and baby’s health. 

So we’re taking a look at the risks of Vitamin D deficiency in pregnancy. But first, why do mama and baby need it? How much is needed? What happens when you’re deficient? How common is deficiency? Where can you get it? And are all supplements the same? 

Vitamin D is crucial for postpartum too. Read about its role in postpartum health here.

Why Vitamin D is Needed

Vitamin D is often referred to as a fat-soluble nutrient, but it is technically a prohormone (a precursor or building block of a hormone). It helps regulate hundreds of genes throughout the body and is critical to the maintenance of healthy bones, muscles, teeth, immune and cardiovascular health, a balanced mood, and cognitive function.

In addition to these important functions for all individuals, Vitamin D is particularly essential during pregnancy for both mama and baby. Mama needs Vitamin D to support her immune function, for the absorption of calcium and phosphorus to maintain bone health, to assist in binding and eliminating toxins, and to support healthy blood pressure. Vitamin D is even essential in preconception and early pregnancy as it is needed to support embryo implantation and pregnancy viability.

Mama’s Vitamin D levels directly affect baby’s Vitamin D levels since Vitamin D is passed via the placenta. Baby needs Vitamin D to help support the formation of bones and teeth, immune system development, proper cell division, and maturation of lungs. Vitamin D can also support pregnancy outcomes, including carrying baby to full term and baby’s adequate birth weight.

Related Reading: Pregnancy Immune Support

The Risks of Deficiency

There is a wide body of recent research indicating that sufficient Vitamin D levels can reduce the risk of numerous pregnancy complications. In addition, research shows that a Vitamin D deficiency can have both short- and long-term effects on baby’s health.

Risks to Pregnancy Outcomes

Research has shown that those who maintain adequate Vitamin D levels during pregnancy have a lower risk of many pregnancy complications, including gestational diabetes, preeclampsia, preterm birth, and bacterial vaginosis.

In fact, one study showed that mothers with adequate blood levels of Vitamin D (>40 ng/mL) had a 60% lower risk of preterm birth. This finding held true even after adjusting for other confounding factors, including race. In women of color, the reduced risk of preterm birth was even higher, at 78%. 

Risks to Baby’s Short- and Long-Term Health

When baby doesn’t get enough Vitamin D in the womb, they can experience short term consequences of Vitamin D deficiency, like low birth weight, low blood calcium levels, and poor growth after birth. 

The risks of deficiency in the womb can permanently impact long term health too. Vitamin D deficiency in the womb can cause dental enamel defects (and increased rates of cavities and dental issues) and lower bone density (and higher rates of fractures). Vitamin D also helps to regulate genetic expression in baby, meaning it can influence what genes are “activated” later in life. Deficiency in the womb can have long-term effects on your baby’s risk of developing insulin resistance and Type 1 Diabetes.

In a 2019 double-blind, randomized controlled trial published in the Journal of the American Medical Association (JAMA) Pediatrics, researchers found that children of mothers who supplemented with a higher dose of Vitamin D (more than three times higher than the current recommended intake) in the third trimester had a 50% lower incidence of enamel defects as measured at age 6 years old. These are referred to as “dental enamel defects of developmental origin,” because they begin in utero and are apparent when the tooth first erupts. The researchers refer to these findings on Vitamin D as “a breakthrough in understanding and prevention of the disease.”

Prevalence of Deficiency

Given the importance of Vitamin D and the risks of deficiency, it’s unfortunate that Vitamin D deficiency in pregnancy is extremely common. 

You might think you eat a pretty balanced diet and spend a decent amount of time in the sun, so you’re probably within reasonable levels. However, research shows that 69% of American women, 65% of Canadian women, 77% of German women, 91% of Chinese women, 96% of Indian women, and 67% of Iranian women have inadequate Vitamin D levels. Plus, these estimates are likely low, as they tend to use standard reference ranges rather than optimal ranges when gathering data. In fact, several of our practitioner partners have reported rates of deficiency in pregnant and lactating women in their practice of over 90%, even in sunny Southern California! 

Even if you’re lucky enough to get sun daily, the amount of UV exposure available for the synthesis of Vitamin D depends on many factors other than just time spent outdoors, including the amount of skin pigmentation you have, your body mass, the latitude and altitude at which you live, the season, the amount of cloud cover, the extent of air pollution, the amount of skin exposed, and how much sunscreen you use.

How Much Do You Need?

Currently, the recommended daily allowance RDA for Vitamin D is set at 600 IU per day for pregnancy. However, numerous studies have shown that this amount is too low and consistently results in Vitamin D deficiency, particularly in women of color.

Unfortunately, despite a wide body of recent research indicating that sufficient Vitamin D levels can reduce the risk of pregnancy complications and promote optimal fetal development, official recommendations for Vitamin D requirements in pregnancy have not been updated.

In fact, several studies conducted on Vitamin D supplementation in pregnant women show that an amount closer to 4,000 IU daily is not only safe, but optimal during pregnancy and that the current RDA of 600 IU is insufficient.  

For example, in one double-blind, randomized controlled trial, pregnant women received either 400 IU, 2,000 IU, or 4,000 IU of Vitamin D3 daily starting between 12 and 16 weeks gestation until delivery. Only 50% of mothers in the group that received the lowest dose (400 IU) had sufficient Vitamin D levels at delivery (and only 20% of Black women in this group had sufficient levels. At the other end of the spectrum, of the women who received the highest dose (4,000 IU), 82% had adequate Vitamin D levels at delivery. In addition, adequate maternal vitamin D levels predicted newborn vitamin D levels (meaning higher dose supplementation significantly reduced the risk of newborn vitamin D deficiency). The researchers found no adverse events linked to any level of Vitamin D supplementation tested and concluded that 4,000 IU per day for pregnant women is safe and was the most effective in achieving Vitamin D sufficiency in all pregnant women and their newborns, regardless of race. We’re proud to say that we considered the most recent research available when formulating our Prenatal Multi Powder and Pills, and both contain the suggested optimal amount of 4,000 IU.

However, while research suggests 4,000 IU likely provides a sufficient amount for pregnancy, just as with other recommendations, this isn’t a foolproof or one-size-fits-all amount. This is because a number of factors affect how much Vitamin D a woman needs, including her Vitamin D levels prior to becoming pregnant, as well as a number of lifestyle factors:

  • where we live (latitude, altitude, pollution)
  • how much sun we get (how much we’re outside each day, how much skin is exposed, how much sunscreen we use)
  • the pigment of our skin (The darker your skin - the more melanin it contains - the more effective it is at blocking UV-B rays and the less vitamin D you’ll absorb

In other words, a dose of 4,000 IU comes much closer to meeting your needs during pregnancy than the current RDA of 600 IU, but the only way to truly know what your levels are and how much more you may need is to test (lots more on that here!). Many healthcare providers can order this test for you, or you can get a simple at-home test to check for yourself.

The recommended intake for postpartum breastfeeding women is 6,000IU. Read more about the role of Vitamin D for postpartum health here.

Types of Vitamin D

When comparing supplement labels, it’s important to understand that there are two different types of Vitamin D - Vitamin D2 and Vitamin D3. 

Vitamin D2

      Vitamin D2, also called ergocalciferol, is a form of Vitamin D made by some plants, mushrooms, and yeast. 

      Vitamin D3

      Vitamin D3, or cholecalciferol, is produced in our skin when the sun’s rays shine on it. We can also get Vitamin D3 by eating egg yolks and fatty fish like salmon, mackerel, or sardines.

      Before our bodies can use either form, they need to be converted into the active form of Vitamin D, calcitriol, by our liver and kidneys.

      Research is clear that Vitamin D3 is more effective at boosting calcitriol levels in the body. In other words, Vitamin D3 is converted into a usable form more efficiently than D2. 

      We include only Vitamin D3 in our Prenatal Multi to support optimal absorption. 

      A Note on Vitamin K2

      In addition, we pair Vitamin D3 with Vitamin K2 (the more absorbable form of Vitamin K). We do this to support optimal bone and heart health, because the interaction between Vitamin D, Vitamin K, and Calcium matters. 

      While Vitamin D helps your intestines efficiently absorb calcium, Vitamin K2 helps direct Calcium into your bones. This ensures that the Calcium you consume is used to strengthen bones (boosting bone health) and does not end up lining the walls of your arteries (damaging cardiovascular health). Yes, this means that even if you consume plenty of Calcium, it will not be properly absorbed without the help of Vitamins D3 and K2.

      Sources of Vitamin D

      Part of the reason for such prevalent Vitamin D deficiency is the lack of availability of Vitamin D in food. For many, the sun is a bigger contributor to Vitamin D status than food. But in almost all cases, it still isn’t enough.

      Vitamin D is found in eggs and fatty fish, and in very small quantities in some mushrooms. Some people obtain Vitamin D from cod liver oil, but the amount (400 IU/teaspoon) is still far from sufficient to meet daily needs.

      While we are proponents of obtaining nutrition from food first, Vitamin D is a prime example of a nutrient that requires supplementation. It’s clear that the vast majority of time, relying on diet and sun exposure alone, particularly in pregnancy, is not enough.

      The Bottom Line

      It’s clear that Vitamin D is essential to mama and baby’s health during and after pregnancy and that the effects of deficiency can have lasting impact on baby’s health. Unfortunately, it’s also clear that the RDA for Vitamin D is woefully understated. We hope this information empowers you to seek the testing and supplementation you need for you and baby to thrive!

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      Hillary Bennetts, Nutritionist

      Hillary Bennetts is a nutritionist and business consultant focusing on prenatal and postpartum health. In addition to nutrition consulting, she provides business consulting and content creation for companies in the health and wellness industry. Hillary spent almost a decade in corporate consulting before shifting gears to combine her lifelong passion for health and wellness with her business background and nutrition education.