Vitamin D—The magical vitamin that our body makes when we bask in the sunshine. In an ideal world, every pregnant woman would soak up vitamin D by relaxing her nine months away somewhere tropical and warm.
But if you can’t pass your pregnancy at the beach and, like most of us, only manage to squeeze in a brief babymoon, then you might want to consider taking supplemental vitamin D, because your prenatal vitamin almost surely does not contain enough of this critical vitamin.
Why? Well, chances are you are not lying at the beach most days. And likely, you aren’t doing all those outdoor, hunter-gatherer activities we performed in our evolutionary past. And when we do venture outdoors, reasonable concerns about skin cancer and skin damage lead us to cover up and wear sunscreen.
But all of these lifestyle changes and safe sun practices have an unfortunate downside. They have led to epidemic levels of vitamin D deficiency, especially among pregnant women.
Vitamin d is critical to prenatal development, but many pregnant women are NOT GETTING ENOUGH.
Studies find that about half of pregnant women are insufficient or frankly deficient in the vitamin. This is true not just in Northern countries like the United States, Canada, and Europe, but even in sun-drenched regions like the Middle East, India, and Brazil.
How much vitamin D do pregnant women need?
Nearly all prenatal vitamins contain vitamin D, usually between 400 and 800 IU (International Units).
Unfortunately, for us mostly indoor, sunscreen wearing pregnant ladies, this amount is only a fraction of what we need.
According to the latest research, pregnant women need at least 2000 IU/day to ensure sufficiency–more than double the amount commonly contained in prenatal vitamins.
I know what you’re wondering. Is that amount safe? Yes.
bottom line…you need more vitamin D for pregnancy.
While you can overdose on vitamin D—it’s fat-soluble so we don’t excrete excessive amounts–overdosing requires huge intakes, usually from very high dose supplements.
Recent studies show that pregnant women can safely consume up to 4000 IU/day without any adverse effects. And fortunately, you cannot overdose on vitamin D from sun exposure. The body limits its sun-based synthesis once you have enough.
What is Vitamin D?
Vitamin D is sometimes called the sunshine vitamin because our skin generates vitamin D when exposed to strong sunlight (think UV index of 3 or above). A few foods, like fatty fish and cod liver oil, also provide vitamin D, but most of us cannot meet our need through diet alone.
We used to worry about getting enough vitamin D to grow and maintain strong bones because it helps us absorb calcium from the food we eat.
But we now know that vitamin D is a potent regulator of the immune system. A majority of immune cells carry receptors for vitamin D, meaning that vitamin D changes how active these cells are.
What are the health benefits in pregnancy?
Epidemiological studies have long shown links between vitamin D and major health benefits like a lower risk of preterm labor and preeclampsia, but it was unclear whether vitamin D caused these benefits.
But in the last five years, numerous randomized clinical trials support the idea the vitamin D actually causes some major health benefits.
There are many benefits of Vitamin D for Pregnancy.
The Known benefits of vitamin D for pregnancy include:
A lower risk of preeclampsia.
Affecting between 4-8% of all pregnancies, preeclampsia is one of the most common and serious disorders of pregnancy. Mild preeclampsia causes high blood pressure and protein in the urine. Uncontrolled, the condition is life threatening. It can rapidly progress to seizures, strokes, liver failure, coma and death. Worldwide, hundreds of thousands of women die from preeclampsia-associated complications every year.
Several randomized clinical trials have found that supplemental vitamin D lowers the risk of preeclampsia, especially when combined with supplemental calcium.  One small randomized trial found that for women who had preeclampsia in a prior pregnancy, high dose supplemental vitamin D cut their risk in half.
Researchers believe that poor blood flow across the placenta, potentially caused by impaired embryo implantation, helps trigger preeclampsia. Vitamin D appears to boost early placental cells’ ability to burrow into the uterine lining, which may be why it lowers the risk of this serious condition. 
And a lower risk of asthma in early childhood.
Two randomized trials found that children whose mothers took vitamin D during pregnancy were less likely to become allergic to dust mites or other common air allergens and had a lower risk of asthma by age 3.
The potential benefits include:
Lower risk of having a small for gestational age (SGA) baby.
A meta-analysis of 13 prospective studies found that being deficient in vitamin D was associated with a 60% greater odds of giving birth to a baby who was SGA .
Lower risk of gestational diabetes.
Deficiency has been linked with a higher chances of gestational diabetes [8,9].
Potential lower risk of preterm birth.
Occurring in roughly 10% of all pregnancies in the United States, preterm birth, or birth before 37 weeks, is the leading cause of infant mortality and morbidity.
Compared to women deficient in vitamin D, women with adequate levels had a 60% lower chance of preterm birth, according to a 2016 meta-analysis. A second meta-analysis found vitamin D supplementation lowered the risk of preterm birth by 40%.
Higher live birth rates among women undergoing fertility treatments.
A meta-analysis of observations studies found that among women undergoing fertility treatments, those with higher levels of vitamin D were more likely to achieve a live birth.
Lower risk of a first trimester miscarriage.
Severe vitamin D deficiency in early pregnancy, defined as blood levels lower than <20 ng/mL, is linked with two-fold greater odds of a first trimester miscarriage .
Given that vitamin D supplements, up to 4000 IU/day, appear to be safe, pregnant women may want to discuss getting some extra vitamin D with their doctors. They need only be aware of one potential issue: the upper limit of 4000 IU/day refers to vitamin D from all food sources and supplements. Prenatal vitamins contain some vitamin D, as does fatty fish and fortified margarine. So women need to keep an eye on all their potential sources.
Learn more about the when, why and how of adding more Vitamin D to your diet with this post from Baby Building Blocks.
- Hollis BW, Johnson D, Hulsey TC, Ebeling M, Wagner CL. Vitamin D Supplementation during Pregnancy: Double Blind, Randomized Clinical Trial of Safety and Effectiveness. J Bone Miner Res. 2011;26: 2341.
- Bodnar LM E al. Maternal vitamin D status and the risk of mild and severe preeclampsia. – PubMed – NCBI [Internet]. [cited 12 Jun 2018]. Available:
- van der Pligt P E al. Associations of Maternal Vitamin D Deficiency with Pregnancy and Neonatal Complications in Developing Countries: A Systematic Review.
- Khaing W E al. Calcium and Vitamin D Supplementation for Prevention of Preeclampsia: A Systematic Review and Network Meta-Analysis.
- Behjat Sasan S E al. The Effects of Vitamin D Supplement on Prevention of Recurrence of Preeclampsia in Pregnant Women with a History of Preeclampsia.
- Kim RH E al. Vitamin D facilitates trophoblast invasion through induction of epithelial-mesenchymal transition.
- Santamaria C E al. Prenatal vitamin D status and offspring’s growth, adiposity and metabolic health: a systematic review and meta-analysis.
- Amraei M E al. Effects of Vitamin D Deficiency on Incidence Risk of Gestational Diabetes Mellitus: A Systematic Review and Meta-analysis.
- Zhang Y E al. Vitamin D and gestational diabetes mellitus: a systematic review based on data free of Hawthorne effect.
- Zhou SS E al. Vitamin D and risk of preterm birth: Up-to-date meta-analysis of randomized controlled trials and observational studies.
- 11. Roth DE E al. Vitamin D supplementation during pregnancy: state of the evidence from a systematic review of randomised trials.
- Zhao J E al. Whether vitamin D was associated with clinical outcome after IVF/ICSI: a systematic review and meta-analysis.
- Zhang H E al. Meta-analysis of the effect of the maternal vitamin D level on the risk of spontaneous pregnancy loss.