Did you know that children might be twice as likely to develop ASDs (autism spectrum disorders) if their moms had vitamin D deficiency during pregnancy? (1)
Considering that as many as 50% of pregnant women in the US may be deficient in vitamin D, that’s a cause for concern. Also, the number goes as high as 98% in some areas of the world. (2)(3)
Moreover, 28% of pregnant women with vitamin D deficiency may have a higher risk of cesarean section and higher risk of preeclampsia (a serious pregnancy complication involving high blood pressure and other symptoms) than women with adequate levels. (4)
With vitamin D deficiency also linked to rickets (soft, weakened bones) in babies and birth defects, you need to have adequate levels of this essential vitamin throughout your pregnancy.
Did you know that we get most of our vitamin D from the sun? But is that enough, or should we get more from food and supplements? Read on to find out.
Why is Vitamin D Important in Pregnancy?
Vitamin D is important for bone development, bone health, and muscle contraction in our bodies.
It regulates calcium homeostasis (for stable levels) by promoting its absorption in the intestines, reabsorption in the kidneys, and movement to and from the bones.
Our bodies produce vitamin D in the form of 25(OH)D or what is known as vitamin D3 (calcifediol). Just like many other essential nutrients, this vitamin crosses the placenta to reach your baby.
Because your baby needs this nutrient for proper development even in the first trimester, you should have good maternal vitamin D status throughout pregnancy.
Adequate levels of maternal and placental vitamin D have plenty of benefits for you and your baby. (5)
Benefits of Vitamin D In Pregnancy – Mothers (Obstetrics)
With increased demands in vitamin D from your baby, your serum vitamin D might become lower than normal.
Having enough vitamin D may help ensure that you’ll have strong muscles and bones throughout your pregnancy.
Studies show that vitamin D may also improve your immune system and help you have better pregnancy outcomes. (6)(7)(8)
Moreover, because vitamin D influences insulin secretion, it may decrease your risk of GD (gestational diabetes) or diabetes in pregnancy, especially during the third trimester. (9)(10)
What Does Vitamin D Do To A Fetus? (Pediatrics)
During the first and second trimesters, your baby’s bone development is at its crucial stage because it develops the collagen matrix for its skeleton.
As your baby’s collagen skeleton begins to develop into bones during the third trimester, there’s also a corresponding increase in the demand for maternal vitamin D. (11)
Neonates (newborn babies) born to mothers with sufficient vitamin D have a bigger size at birth and a reduced risk of preterm birth than those whose moms suffered from deficiency. (12)
But the benefits appear to go beyond the baby’s development.
Higher maternal vitamin D levels during pregnancy may lead to greater IQ scores in their offspring. (13)
While the direct link between asthma and vitamin D remains unclear, a 2007 study found a reduced risk of recurrent wheezing (a symptom of asthma) in young children whose moms had a higher vitamin D intake during pregnancy. (14)
Why is the Sun Important in Vitamin D Production?
Our bodies make vitamin D from cholesterol when our skin is exposed to sunlight. The UV (ultraviolet) rays of the sun activate the production of this vitamin on the skin.
Without the sun’s help, our bodies can’t produce vitamin D. Moreover, the sun’s UV rays should touch the skin before the production starts.
That’s why factors such as clothing (wearing long sleeves), seasons (less sun in winter), and substances (use of sunscreen) affect vitamin D production in our bodies.
Although some food sources are rich in vitamin D, dietary intake only provides around 10% of our body’s reserves.
How Much Vitamin D Should You Take In Pregnancy?
The Endocrine Society recommends at least 1500–2000 IU/d of vitamin D to maintain adequate 25(OH)D levels (above 75 nmol/L) for pregnant and lactating moms. (11)
Effects of Vitamin D Deficiency in Gestation
The WHO (World Health Organization) and IOM (Institute of Medicine) define vitamin D deficiency as 25(OH)D serum levels lower than 50 nmol/L or below 20 ng/mL.
RCT (randomized controlled trials) show that vitamin D deficiency may have plenty of adverse effects in moms during gestation, including increased risks of: (15)(16)
- Repeated pregnancy loss
- Cesarean section
- Gestational diabetes mellitus (diabetes during pregnancy)
- Pregnancy-induced hypertension (high blood pressure)
- Preterm delivery (premature birth)
- Postpartum depression
Pregnant moms may also have a higher risk for severe postpartum hemorrhage if they have low vitamin D. (17)
Children are also affected by vitamin D deficiency in maternal serum, which may lead to a higher risk of: (18)
- Rickets in children (softened, weakened bones)
- Osteoporosis (bone loss)
- Osteomalacia (soft, easily fractured bones)
- Neonatal hypocalcemia (muscle cramps in newborn babies)
- Problems in baby’s bone development
- Enlarged size of cranial fontanelles (baby’s soft spot on the skull)
- Asthma and impaired lung function
- Type 1 diabetes
In her book, Brain Health from Birth, molecular biotechnologist and biochemist Rebecca Fett explains: (19)
“Even if preventing preterm birth is the only reason to supplement with vitamin D, this is an incredibly compelling reason since preterm birth has so many potential downstream consequences, including risks of infections, hearing loss, serious intellectual disability, autism, ADHD, and even milder cognitive impairments.”
Who is at Risk of Vitamin D Deficiency?
The prevalence of vitamin D deficiency is high for people living in the US and other areas in the temperate zone, especially during the autumn and winter months.
That’s why it’s a good idea for you to soak up the sun from early spring to late summer to minimize the risk factors. (20)
Surprisingly, the prevalence of vitamin D deficient moms is also high even in areas with lots of sunlight, such as in tropical countries.
Researchers highlight that this could be due to lesser sun exposure because of sunscreen use or wearing clothing with long sleeves as protection from the sun. (21)
Recent studies also show that more people have a higher risk of vitamin D deficiency due to: (5)(22)
- Current lifestyle of lesser outdoor activities
- Staying indoors to reduce risks of skin cancer
- Increasing obesity rates (vitamin D is stored in fats that the body can’t use)
- Veiled clothing
- Poor dietary vitamin D intake
- Darker skin
Should All Pregnant Women Be Screened for Vitamin D Deficiency?
The best way to screen for vitamin D deficiency is to measure serum 25(OH)D (serum 25-hydroxyvitamin D) levels.
There are currently no recommendations for universal screening, but most OBGYNs in the US include vitamin D screening as a routine. (23)
Alternatively, maternal vitamin D status may be tested using a 24-hour urine calcium excretion rate. That’s because vitamin D deficiency often leads to low levels of calcium and phosphorus in the blood.
Still, there’s insufficient evidence for the ACOG (American College of Obstetricians and Gynecologists) to recommend screening for maternal vitamin D deficiency in all pregnant women. (24)
But some nutritionists disagree.
In her book, Real Food in Pregnancy, registered dietitian Lily Nichols wrote: (3)
“In some areas of the world, vitamin D deficiency affects up to 98 percent of pregnant women. At the same time, supplementing with this nutrient is effective at reversing deficiency and is incredibly inexpensive.
It’s perplexing to me that identifying and correcting vitamin D deficiency is not the norm, especially given that it puts you at higher risk for preeclampsia, having low-birth-weight infants, and gestational diabetes.”
Foods Rich in Vitamin D
Unfortunately, vitamin D insufficiency is difficult to treat with just food because only a few dietary sources contain this nutrient.
Also, most vitamin D concentrations in these foods may not be high enough to provide adequate nutrients to your body. (20)
These food sources have vitamin D3:
- Cod liver oil
- Oily fish
- Canned sardines
- Beef liver
- Fortified foods (milk, juices, yogurts, and cereals)
Vitamin D2 may be found in some dietary vegetable sources such as:
- UV-treated mushroom powder
Of all these food sources, the NIH (National Institutes of Health) points out that only cod liver oil (1,360 IU per 1 tbsp serving size) contains significant amounts of vitamin D.
Trout and salmon (3 oz serving size each) have 645 IU and 570 IU, respectively. But the rest of the food items on the list contain levels lower than 400 IU. (20)
Is It Safe To Take D Vitamin During Pregnancy?
Food alone can’t meet vitamin D requirements, so supplementation is recommended, especially for pregnant women.
The Endocrine Society recommends a prenatal vitaminwith 400 IU vitamin D plus a supplement with at least 1000 IU vitamin D for pregnant women. (25)(26)
It’s also best to start taking vitamin D in early pregnancy.
This vitamin comes in two metabolites:
- Vitamin D2 (ergocalciferol)
- Vitamin D3 (cholecalciferol)
But which one is a better supplement?
Rebecca Fett has great advice regarding this matter: (19)
“When choosing a supplement, note that the preferred form is vitamin D3, which is more effective than vitamin D2 in raising blood concentrations. For even better absorption, it is best to choose an oil-based capsule or liquid drops.”
To help maximize absorption, researchers recommend that you should take both D2 and D3 supplements with a meal containing fat. (23)
Can Too Much Vitamin D Be Harmful In Pregnancy?
Some moms-to-be might feel worried about the effect of vitamin D if given in high doses during antenatal (pregnancy care or maternity care).
A 2011 study in the Journal of Bone and Mineral Research shows that vitamin D supplementation of 4,000 IU/day may be safe for pregnant women, regardless of race. The same dosage may also be effective for the babies in their tummies.
Meanwhile, current recommendations of 400 to 2,000 IU (international units) of vitamin d supplements may be inadequate, especially in African Americans. (27)
But the Endocrine Society guidelines show that supplementing with 6,000 IU of vitamin D for two weeks may be safe for pregnant women with severe deficiencies. Afterward, they have to continue with a lower maintenance dose. (11)
Though there are only a few observational studies done about the effects of excess vitamin D, researchers point out that this is partly because of our kidney’s ability to control calcitriol levels (an active form of vitamin D) in our bodies.
They believe that there may be nothing to fear when taking a higher dose of vitamin D because the benefits outweigh the risks.
Recent studies have shown that toxicity may occur after ingesting very large amounts (>10,000 IU/d) of the vitamin, but only when done for prolonged periods. (23)(5)
If used beyond recommended levels, vitamin D may cause toxicity that’s shown through these symptoms: (28)
- Pruritus (strong urge to scratch skin)
- Polyuria (excessive urination)
- Polydipsia (excessive thirst)
Renal (kidney) failure may happen if vitamin D toxicity is left untreated.
Hydration using IV normal saline may help treat the condition and quickly lower blood calcium levels. However, kidney damage may be irreversible.
Does My Prenatal Vitamins Have Enough Vitamin D?
Most prenatal vitamins and multivitamins do not contain enough vitamin D. Although concentrations differ among brands and preparations, these only ranges between 100 IU and 800 IU. (15)
Vitamin D Benefits Beyond Pregnancy
Breast milk may not always provide enough vitamin D for your baby. That may be true even in well-nourished women. (29)
The Endocrine Society recommends supplements with at least 1400–1500 IU/d for breastfeeding moms to meet their babies’ needs. That’s because breastfeeding moms need to have at least 4000 to 6000 IU/d during lactation before we can transfer enough vitamin D into our breastmilk. (27)
Care must be taken for vitamin D supplementationin pediatrics.
Although the incidence of overdose is rare even in children, a 2014 study in The Journal of Clinical Endocrinology and Metabolism shows that it is possible and may be due to errors in prescription and vitamin manufacturing or formulation. (30)
The US Food and Nutrition Board mandates fortification of infant milk with 40–100 IU vitamin D while Canada requires 40–80 IU. (20)
(10) Chen GD, Pang TT, Li PS, Zhou ZX, Lin DX, Fan DZ, Guo XL, Liu ZP. Early pregnancy vitamin D and the risk of adverse maternal and infant outcomes: a retrospective cohort study. BMC Pregnancy Childbirth. 2020 Aug 14;20(1):465. doi: 10.1186/s12884-020-03158-6. PMID: 32795269; PMCID: PMC7427871. https://pubmed.ncbi.nlm.nih.gov/32795269/
(14) Camargo CA Jr, Rifas-Shiman SL, Litonjua AA, Rich-Edwards JW, Weiss ST, Gold DR, Kleinman K, Gillman MW. Maternal intake of vitamin D during pregnancy and risk of recurrent wheeze in children at 3 y of age. Am J Clin Nutr. 2007 Mar;85(3):788-95. doi: 10.1093/ajcn/85.3.788. PMID: 17344501; PMCID: PMC4406411.
(16) Bodnar LM, Platt RW, Simhan HN. Early-pregnancy vitamin D deficiency and risk of preterm birth subtypes. Obstet Gynecol. 2015 Feb;125(2):439-447. doi: 10.1097/AOG.0000000000000621. PMID: 25569002; PMCID: PMC4304969. https://pubmed.ncbi.nlm.nih.gov/25569002/
(17) Cochrane. https://www.cochrane.org/CD008873/PREG_vitamin-d-supplementation-beneficial-or-harmful-women-during-pregnancy
(18) Holick MF, Chen TC. Vitamin D deficiency: a worldwide problem with health consequences. Am J Clin Nutr. 2008 Apr;87(4):1080S-6S. doi: 10.1093/ajcn/87.4.1080S. PMID: 18400738. https://pubmed.ncbi.nlm.nih.gov/18400738/
(22) Karras SN, Anagnostis P, Annweiler C, Naughton DP, Petroczi A, Bili E, Harizopoulou V, Tarlatzis BC, Persinaki A, Papadopoulou F, Goulis DG. Maternal vitamin D status during pregnancy: the Mediterranean reality. Eur J Clin Nutr. 2014 Aug;68(8):864-9. doi: 10.1038/ejcn.2014.80. Epub 2014 May 14. PMID: 24824015. https://pubmed.ncbi.nlm.nih.gov/24824015/
(25) https://pubmed.ncbi.nlm.nih.gov/21646368/ (https://academic.oup.com/jcem/article/96/7/1911/2833671)
(26) Tripkovic L, Lambert H, Hart K, Smith CP, Bucca G, Penson S, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: A systematic review and meta-analysis. Am J Clin Nutr 2012;95:1357-64. https://pubmed.ncbi.nlm.nih.gov/22552031/
(27) Hollis BW, Johnson, D., Hulsey, T. C., Ebeling, M., & Wagner CL (2011). Vitamin D supplementation during pregnancy: double-blind, randomized clinical trial of safety and effectiveness. Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research, 26(10), 2341–2357. https://doi.org/10.1002/jbmr.463. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3183324/.
(29) Picciano MF. Nutrient composition of human milk. Pediatr Clin North Am 2001;48:53-67. https://pubmed.ncbi.nlm.nih.gov/11236733/
(30) Vogiatzi MG, Jacobson-Dickman E, DeBoer MD; Drugs, and Therapeutics Committee of The Pediatric Endocrine Society. Vitamin D supplementation and risk of toxicity in pediatrics: a review of current literature. J Clin Endocrinol Metab. 2014 Apr;99(4):1132-41. doi: 10.1210/jc.2013-3655. Epub 2014 Jan 23. PMID: 24456284. https://pubmed.ncbi.nlm.nih.gov/24456284/