If you’re pregnant, then you know where your child is, but do you know what your blood level of vitamin D is? Better yet, find out your vitamin D status before you become pregnant.

A burgeoning body of evidence is illuminating the extreme importance of maintaining an adequate vitamin D level during pregnancy – for the health of mom, her developing baby, and the delivery outcome.

In the body, 25-hydroxyvitamin D is activated to 1,25 dihydroxyvitamin D as it is needed. Between early pregnancy and the third trimester, activated vitamin D increases two- to three-fold, illustrating its importance to the developing baby, who depends entirely on maternal vitamin D stores.

Insufficient vitamin D is common during pregnancy.

Even if you are not pregnant, a vitamin D deficiency is quite common; by many estimates more than 40% of U.S. adults have an inadequate vitamin D level.1

And low levels of vitamin D appear to be even more common during pregnancy. In a study of 235 U.S. women in their first trimester of pregnancy, a whopping 70% had insufficient serum levels of vitamin D (defined as less than 30 ng/mL).2

What are some risk factors for low vitamin D?

Since it’s not uncommon for a woman to begin her pregnancy with a low vitamin D level, let’s take a look at some causes of insufficient vitamin D. Vitamin D is unlike other vitamins because we can both make our own, as well as obtain it from outside sources (diet and supplements). Our skin makes vitamin D when it has adequate exposure to sunlight.

Unfortunately, many individuals don’t receive the necessary amount of sun exposure required to achieve sufficient vitamin D needs.

This can occur for many reasons, such as living in a place with long winters, which can significantly reduce vitamin D production from November to March, wearing clothing that covers most of the skin, spending long hours indoors, wearing sunscreen with an SPF greater than 8, and having naturally darker skin. 

Other factors that can contribute to a low level of vitamin D include low dietary intake, kidney disease, liver disease, obesity, and malabsorption (due to gastrointestinal disorders or surgery, such as gastric bypass).

Even environmental pollution can affect your vitamin D level.

This is because air pollution can partially block exposure to the sun’s UV rays necessary to manufacture vitamin D in your skin. In a study of 3,285 pregnant Chinese women, air pollution measured by particulate levels was associated with lower vitamin D levels during the third trimester.3 Of course, air pollution is more significant in China than it is in the United States, but this is still food for thought.

Maintenance of adequate vitamin D status can benefit the health of a pregnant woman.

Numerous studies show that maintaining an optimal level of vitamin D during pregnancy can decrease complications for both mom and baby.

A study at the Medical University of South Carolina of 500 pregnant women found that those women who took 4,000 IU of vitamin D daily (in addition to a prenatal multi with 400 IU daily) during the second and third trimester of pregnancy had half the risk of pregnancy-related complications, compared to women who took just the 400 IU vitamin D daily.4 

At the beginning of the study, despite the sunny climate of South Carolina, 94% of African-American women, 66% of Hispanic women, and 50% of Caucasian women had either low or insufficient levels of vitamin D.

Can vitamin D levels during pregnancy affect the future health of a child?

Right from day one, vitamin D status during pregnancy can affect a newborn infant. A meta-analysis of 13 randomized, controlled trials found that vitamin D supplementation during pregnancy was associated with significant improvements in the incidence of low birth-weight or small-for-gestational-age infants, and was positively associated with greater birth weight, length, and head circumference.5

Other research has found maintenance of a vitamin D level above 30 ng/mL (the lower level of what is typically considered adequate) during pregnancy can significantly improve offspring’s future respiratory health.

An analysis of two studies found that pregnant women who consumed between 2,400 and 4,000 IU of vitamin D daily gave birth to children with an average 25% decreased risk of wheezing and other respiratory issues between birth and age three.6

Children whose mothers were deficient in vitamin D during pregnancy are at greater risk of being overweight later on. In one study, women in the lowest one-third for vitamin D status had children with greater waist circumferences and body mass indexes at pre-school age, which persisted at least up to age six, compared to the offspring of women who had sufficient vitamin D during their pregnancies.7

Other studies have found similar associations between the vitamin D status of a woman during pregnancy and the future body weight of her offspring.8

The vitamin D level of an infant at birth can even affect health outcomes in adulthood. A study of more than 3,000 Danish infants found that those infants with the lowest vitamin D levels at birth (Denmark has been banking neonatal vitamin D level information since 1981) had a 44% increased risk of developing mental health issues as an adult.9

If you are planning a pregnancy, then consider testing your vitamin D level with Thorne’s easy, at-home Vitamin D Test. If you are already pregnant, then be sure to consult with your health professional about your vitamin D status and appropriate supplementation.


  1. Forrest K, Stuhldreher W. Prevalence and correlates of vitamin D deficiency in US adults. Nutr Res 2011;31(1):48-54.
  2. Flood-Nichols S, Tinnemore D, Huang R, et al. Vitamin D deficiency in early pregnancy. PLoS One 2015;10(4):e0123763. doi: 10.1371/journal.pone.0123763.
  3. Zhao Y, Wang L, Liu H, et al. Particulate air pollution exposure and plasma vitamin D levels in pregnant women: a longitudinal cohort study. J Clin Endocrinol Metab 2019 Mar 21. pii: jc.2018-02713. doi: 10.1210/jc.2018-02713. [Epub ahead of print]
  4. High doses of vitamin D may cut pregnancy risks. https://www.webmd.com/baby/news/20100504/high-doses-of-vitamin-d-may-cut-pregnancy-risk#1 [Accessed 4.3.19]
  5. Maugeri A, Barchitta M, Blanco I, et al. Effects of vitamin D supplementation during pregnancy on birth size: a systematic review and meta-analysis of randomized controlled trials. Nutrients 2019;11:442; doi:10.3390/nu11020442
  6. Wolsk H, Chawes B, Litonjua A, et al. Prenatal vitamin D supplementation reduces [respiratory issues] in early childhood: A combined analysis of two randomized controlled trials. PLoS One 2017;12(10):e0186657. doi: 10.1371/journal.pone.0186657. 
  7. Daraki V, Roumeliotaki T, Chalkiadaki G, et al. Low maternal vitamin D status in pregnancy increases the risk of childhood obesity. Pediatr Obes 2018;13(8):467-475. 
  8. Miliku K, Felix J, Voortman T, et al. Associations of maternal and fetal vitamin D status with childhood body composition and cardiovascular risk factors. Matern Child Nutr 2019;15(2):e12672. doi: 10.1111/mcn.12672. Epub 2018 Sep 21.
  9. Eyles D, Trzaskowski M, Vinkhuyzen A, et al. The association between neonatal vitamin D status and [mental health]. Sci Rep 2018;8(1): 17692. doi: 10.1038/s41598-018-35418-z