by: Hillary Jarnagin, MD
If you are among the expectant mothers in our practice, you may have been diagnosed with vitamin D deficiency after your initial routine obstetrical labs returned and may be receiving or have received what must seem like a whopping weekly dose of vitamin D to correct the deficiency. You may be wondering why we check vitamin D levels at all, how you could have a vitamin deficiency when you eat well and take your prenatal vitamins, and why the dose on your vitamin D prescription has so many zeroes in it. Let me take a few moments to explain. We at Frisco Women’s Health have instituted a practice of routine vitamin D testing as part of our initial prenatal assessment. While this practice is not universal for all obstetricians, we believe this is an important intervention for the majority of our patients.
Vitamin D has a crucial role in maintenance of appropriate blood calcium levels and healthy bones in mothers. Since maternal vitamin D level in the blood is the exclusive source of vitamin D for a baby in the womb, it is also vital for the development of healthy bones and muscles in her baby.1 In pregnancy, low vitamin D levels have been associated with increased risk of Cesarean delivery, bacterial vaginosis, pre-eclampsia, and impaired glucose metabolism.1 Over the past several years, Vitamin D has garnered a lot of attention both in the lay press and the medical literature not only for its importance in bone health but also for its role in chronic disease like cancer, autoimmune disorders, glucose metabolism, cardiovascular disease, and mood and psychiatric disorders. Research is ongoing in the extraskeletal activities of vitamin D. In the past decade, we have also come to discover that a significant portion of the population of the United States are insufficient or deficient in Vitamin D. In fact, one study demonstrated that about 30% of adults were vitamin D deficient and almost all of the remaining 70% were in the suboptimal range.2 If these statistics are accurate and adequate vitamin D is important for both a mother and her growing baby, then clearly, there is a valid rationale to screening all women for vitamin D deficiency and correcting it in the likely event that it is found. So, how it is possible in a country with as much wealth and access to good nutrition that almost all Americans have suboptimal vitamin D levels?
Though it is called a “vitamin” meaning a nutrient that we need to live but cannot synthesize ourselves and thus must obtain from our diet, vitamin D could more accurately be classified as a hormone. Hormones are a chemical substances made by one organ in our body that are then released into the blood to have an effect of a distant target organ or tissue. In the case of vitamin D, few foods, even those that are fortified with vitamin D, have sufficient amounts to meet our daily needs or to correct vitamin D deficiencies. Dietary sources of vitamin D include the skin of fatty fish, fish liver, beef liver, egg yolks, and fortified dairy and juices.
Vitamin D can by synthesized in the skin by ultraviolet light from the sun, and from there, it travels through the blood and has receptors in at least 10 different organ and tissue types including brain, breast, colon, muscle and the pancreas.1 If we can make our own vitamin D with sunlight, why is vitamin D deficiency so pervasive? Sunblock effectively keeps the ultraviolet rays that can potentially cause skin cancer from penetrating the skin. Unfortunately, these same ultraviolet rays are the ones required to make vitamin D. Other risk factors for vitamin D deficiency include staying indoors, wearing more clothing that covers the skin (either from cold winter weather, long winter/short summer in northern latitudes, or for cultural reasons), and obesity. Melanin, the pigmentation substance in the skin, reduces the production of vitamin D so darker skinned individuals are at greater risk for insufficiency or deficiency.
As we age, our ability to produce vitamin D naturally declines as well. Those who have kidney failure, advanced liver disease, or malabsorption from the gastrointestinal tract either from inflammatory bowel disease, celiac disease, pancreatic insufficiency, or bariatric surgery can be at substantially increased risk for deficiency. Finally, certain medications like chronic steroid use and some anti-seizure medications can predispose to vitamin D deficiency. With these risk factors in mind, it is easy to understand how most Americans become vitamin D insufficient. We can’t get enough from our diet, about half of our population is overweight or obese, most of us spend our time almost exclusively indoors, and when we do go outside, we dutifully apply sunscreen in the spring and summer and the appropriate layers of clothes in fall and winter. It’s no wonder vitamin D insufficiency and deficiency affect the majority of the population.
Screening for vitamin D deficiency is performed by checking a serum 25 hydroxy-vitamin D level (25 OHD). Deficiency is defined as a serum 25 OHD level < 20 ng/mL, and those with this level of deficiency are at risk of disorders of bone metabolism like osteoporosis or osteomalacia. Serum 25 OHD levels between 21-29 ng/mL are considered suboptimal; while this level of vitamin D is able to protect from pathologic bone loss, it may not be sufficient for the additional roles that vitamin D plays in other tissues and organs. Optimal vitamin D levels are between 30-50 ng/mL. Toxicity is uncommon and usually does not occur below serum levels of about 100 ng/mL.
The recommended daily allowances for vitamin D in adults is 600 IU per day. The Institute of Medicine does not make any recommendations to increase vitamin D intake in pregnancy or lactation despite maternal vitamin D in the blood and breast milk being the exclusive sources of vitamin D in the fetus and the breast fed infant, respectively. In our vitamin D deficient or insufficient pregnant patients, our goal of treatment is to return the vitamin D to the optimal range (> 30 ng/mL) to ensure adequate levels for both mother and baby. Initially, vitamin D deficient patients will receive 50,000 IU/week. While this seems like a lot, and it is, this dose is often what is required to correct deficiency. To put things in perspective, a fair skinned person with fully exposed skin in midday sun can make about that much vitamin D in 30 minutes. Before anyone asks for a prescription to a tanning salon, the UV light from a tanning bed cannot correct vitamin D deficiency…sorry. Once the deficiency has been corrected, the dose can be reduced for maintenance. In patients who have a history of kidney stones, we may reduce the dose or duration of vitamin D supplementation or monitor urine calcium levels to reduce the risk of a recurrent episode.
While the role Vitamin D in various organs and tissues and the extent to which vitamin D supplementation can prevent or correct chronic disease is an area of ongoing investigation, its role in the development and maintenance of healthy bone is well-established. For this reason alone, we feel that identifying vitamin D deficiency and normalizing Vitamin D levels through adequate supplementation in all of our pregnant patients is indicated.
1. Althaus, Jayne et al. Vitamin D and Pregnancy: 9 Things You Need to Know. OBG Mgmt. 2011 August; 23 (8): 30-36.
2. Manson, Joann and Emily Szmuilowicz et al. How much vitamin D should you recommend to your nonpregnant patients? OBG Mgmt. 2011 July; 23 (7): 44-53.
3. Bouillon, Roger et al. Vitamin D and Extraskeletal Health. UpToDate. 2016 September.
4. Pazirandeh, Sassan and David L. Burns. Overview of Vitamin D. UpToDate. 2016 January
5. Garner, Christine D. Nutrition in Pregnancy. UpToDate. 2016 November.
6. Dawson-Hughes, Bess. Vitamin D Deficiency in Adults. UpToDate. 2016 November.