May 10, 2009

research paper: vitamin d in pregnancy

Vitamin D is a fat-soluble vitamin that has recently jumped into the forefront of health and nutrition. Previously thought of as a vitamin needed only in small amounts to prevent rickets in children, vitamin D deficiency is now recognized as important for much more than just bone health. Vitamin D status is important for everybody, but it is especially important during pregnancy, because low maternal vitamin D stores may contribute to problems such as low birthweight and small for gestational age babies (a serious problem in the United States) and an increased risk later on for many other diseases.

Vitamin D is not a simple vitamin but a prohormone, a complex molecule that plays many important roles in the body. These roles, in addition to the main function of regulating mineral salt deposition in bones, include regulation of body metabolism, mood, blood pressure, and immune function – maybe even protection against some forms of cancer (Wardlaw & Hampl, 2007). Vitamin D is synthesized in the skin when the right wavelength of sunlight is available, and it is found in a few foods such as cod liver oil and fortified milk. Unfortunately, these two routes of acquisition are seldom sufficient for vitamin D needs, especially for people living in northern climates (defined as above 42 degrees north latitude – a line between northern California and Boston, Massachusetts) and in climates with frequent cloud cover preventing the absorption of ultraviolet light from the sun (National Institutes of Health [NIH], 2008). Location and climate are not the only factors that can limit vitamin D synthesis from the sun; genetics and cultural practices can also play a role. Australian researchers Grover and Morley (2001) reported that among pregnant women who were either dark-skinned or regularly wore a veil, 80% were below reference values for vitamin D.

Insufficient amounts of vitamin D in the body can cause rickets (bone malformation) in children, osteomalacia (bone softening) in adults, and can contribute over a lifetime to the chance of developing osteoporosis in later life. Other health effects caused or influenced by inadequate vitamin D supply in the general population include muscle weakness and inflammation (NIH, 2008). In pregnancy, having an adequate supply of vitamin D is especially important because of the health impacts on the developing fetus. Mothers who do not have an adequate supply of vitamin D cannot provide their baby with an adequate supply of vitamin D. A study by Bodnar, Simhan, and Powers (2007) reports in the Journal of Nutrition that in pregnant women who were vitamin D deficient, newborns were either as deficient as their mother or more deficient (in some cases by as much as 16%) than their mother. This data was taken from women living in northern latitudes of the United States who used prenatal vitamins (which presumably provided vitamin D) as directed by their doctor.

Babies who are born deficient in vitamin D have lower birthweights and tend to remain smaller throughout life. Low birthweight is associated with a wide range of complications that can be lasting, including breathing difficulties, heart problems, and increased risk of infection (March of Dimes Foundation, 2009). A recent study showed that children whose mothers had insufficient levels of vitamin D during pregnancy had lower bone mass and mineralization both at birth and at a follow-up study nine years later (Gale et al., 2008), indicating that vitamin D deficiencies can prevent children from reaching their full potential. In a study completed in 1980 Brooke et al. showed that babies born to mothers in the control group (those not receiving vitamin D supplements) were twice as likely to be labeled “small for gestational age,” and they were more likely to have larger-than-normal fontanelles (or “soft spots”) which the authors thought was indicative of incomplete skull ossification during gestation. The authors recommended that all pregnant women be given supplements of at least 1,000 IU of vitamin D daily, but they received little attention at the time.

In addition to being smaller, vitamin D deficient babies also have an increased risk for a wide range of diseases later in life that may be linked to the innate immune system. These are mostly chronic, slowly developing diseases such as Type I and Type II diabetes, schizophrenia, autoimmune disorders such as multiple sclerosis and rheumatoid arthritis (Wagner, Taylor, & Hollis, 2008), and maybe even neural tube defects such as spina bifida (Hollis & Wagner, 2006).

The circulating form of vitamin D in the blood, called 25(OH)D, is utilized directly by many cells in the body, including monocytes and macrophages, important immune system components. Tissue cells such as prostate, breast, colon, lung, and keratinocytes (in the skin, hair, and nails) also have direct receptors for 25(OH)D, and there has been speculation about whether all body cells may contain receptors for vitamin D (Wagner, Taylor & Hollis, 2008). Vitamin D acts in the tissue cells to modulate cell proliferation (important in cancer), differentiation, and apoptosis (programmed cell death, also important in cancer) (NIH, 2008). Vitamin D is known to have a regulatory effect on the immune system, and high levels of vitamin D are associated with reduced risk of autoimmune diseases (Hyppönen, 2005).

Preeclampsia, a serious complication of pregnancy, may be related to autoimmune diseases and may be influenced by vitamin D status (Hyppönen, 2005). Preeclampsia causes the mother’s blood pressure to rise and may be fatal to the mother, the baby, or both. Preeclampsia is not uncommon, affecting about 10% of pregnancies in the United States and causing 18% of maternal deaths in the United States. Preeclampsia causes babies to be born prematurely because of the danger to both mother and baby if pregnancy is continued, thereby causing a wide range of lasting health problems (Preeclampsia Foundation, 2008). Preeclampsia is more common in women with a history of autoimmune disorders, and some research has already shown that women with adequate levels of vitamin D before and during pregnancy have lower incidences of preeclampsia (Hyppönen, 2005).

The current recommendations for vitamin D intake were made 40 years ago, and were based on the amount of vitamin D contained in a teaspoon of cod liver oil. This amount was thought to be sufficient based only on anecdotal evidence and before it was possible to measure blood levels of 25(OH)D, the usable form of vitamin D in the body (Hollis & Wagner, 2006). The recommendation for pregnancy of 400 IU per day has been shown in numerous studies to either have no effect on blood serum levels of 25(OH)D or to actually decrease circulating levels of 25(OH)D. This explains why women taking prenatal vitamins as directed are still deficient in vitamin D. The upper limits for vitamin D of 2,000 IU per day were also set somewhat arbitrarily based on reports of vitamin D toxicity from the 1920’s, when researchers gave children between 3,000,000 and 18,200,00 IU of vitamin D a day, extreme pharmacological doses (Wagner, Taylor & Hollis, 2008). One brief exposure of the entire body to sunlight can synthesize up to 25,000 IU of vitamin D, and several studies have given subjects up to 10,000 IU of vitamin D daily with no adverse effects (Hollis & Wagner, 2006). It has been found that in most people, between 1,000 and 5,000 IU of vitamin D daily will raise blood levels of 25(OH)D to normal, adequate levels (Wagner, Taylor & Hollis, 2008).

Vitamin D is no longer a simple vitamin to be easily overlooked. It is an important prohormone that regulates many body systems and can decrease the risk of some common diseases, many of which have no cure. Many people worldwide and most people residing in northern climates do not have sufficient levels of vitamin D, and cannot achieve sufficient levels through diet and sun exposure alone. Most people would benefit from taking a vitamin D supplement in order to maximize health. During pregnancy sufficient levels of vitamin D are especially important in order to provide the developing baby with the vitamin D it needs. Pregnant women should make sure to take a vitamin D supplement of at least 1,000 IU per day of vitamin D to reduce the risk of giving birth to a low birthweight or small for gestational age baby, to reduce the baby’s later risk for disease, and possibly to reduce the risk of developing preeclampsia during pregnancy.


Bodnar, L.M., Simhan, H.N., & Powers, R.W. (2007). High prevalence of vitamin D insufficiency in black and white pregnant women residing in the northern United States and their neonates. Journal of Nutrition, 137(2), 447-452.

Brooke, O.G., Brown, I.R., Bone, C.D., Carter, N.D., Cleeve, H.J., Maxwell, J.P., et al. (1980). Vitamin D supplements in pregnant Asian women: effects on calcium status and fetal growth. British Medical Journal, 280(6216), 751-754.

Gale, C. R., Robinson, S.M., Harvey, N.C., Javaid, M.K., Jiang, B., Martyn, C.N., et al. (2008). Maternal vitamin D status during pregnancy and child outcomes. European Journal of Clinical Nutrition, 62, 68-77.

Grover, S.R., and Morley, R. (2001). Vitamin D deficiency in veiled or dark-skinned pregnant women. Medical Journal of Australia, 175, 251-252.

Hollis, B. W., and Wagner, C. L. (2006, April 25). Nutritional vitamin D status during pregnancy: reasons for concern. Canadian Medical Association Journal, 174(9), 1287-1290.

Hyppönen, E. (2005, July). Vitamin D for the Prevention of Preeclamsia? A Hypothesis. International Life Sciences Institute, 63(7), 225-232.

March of Dimes Foundation (2009). Low Birthweight. Retrieved April 20, 2009 from

National Institutes of Health: Office of Dietary Supplements (2008). Dietary Supplement Fact Sheet: Vitamin D. Retrieved April 18, 2009 from

Preeclampsia Foundation (2008). About Preeclampsia. Retrieved April 20, 2009 from

Wagner, C. L., Taylor, S. N., and Hollis, B. W. (2008). Does Vitamin D Make the World Go ‘Round’? Breastfeeding Medicine, 3(4), 239-250.

Wardlaw, G.M., and Hampl, J. S. (2007). Perspectives in Nutrition (7th ed.). New York: McGraw-Hill.


Donna Mitchell said...

Thanks for this great article!!


gail hart said...

I think future research recommend and increase for pregnant women above the current RDA of 400 to 600 IUs.

I think though that it is too soon to advise a supplement of 1000IU daily in pregnancy.

We might find that an optimum total dietary intake -- (which includes any supplement) -- may be closer to 1000 IU, but I think a we should be careful to avoid excess intake of vitamin D. Excess amounts of supplement can be harmful and we do not yet know the upper safe limit in pregnancy.
Until we do, I'm a midwife who advises women to be cautious and to keep their supplements within the doses advised by the current RDA.

Anonymous said...

The amount of vitamin D a human needs is that amount which brings their blood level to 50 to 80 ng/ml. One dose doesn't fit all.

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