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Effects of Vitamin D Deficiency During Pregnancy

Vitamin D has long been recognized for its beneficial effect on bone health; however, in recent years there is an increased understanding of the role that vitamin D plays in regulation of cell growth, immunity, and cell metabolism. Because vitamin D receptors can be found in most tissues and cells in the body, the impact of a vitamin D deficiency on the developing fetus and maternal health is a significant concern. A high prevalence of vitamin D deficiency is now recognized in pregnant women.
One consequence of vitamin D deficiency, documented by researchers at the University of Pittsburgh, is an increased risk for pre-eclampsia. This risk was especially prevalent among African-American women, whose ability to synthesize vitamin D from ultraviolet light requires much greater exposure than it does in white women. With increasing vitamin D levels, the risk for pre-eclampsia was significantly reduced.
Other studies have explored the role of vitamin D deficiency in the development of insulin resistance. A correlation has been found between obesity and vitamin D levels. A 2-fold increase in the odds of a mid-pregnancy vitamin D deficiency has been documented among women with body mass indices between 22 and 34.
Although rare, severe maternal vitamin D deficiency can lead to rickets in the developing fetus. Evidence is accumulating that even less severe vitamin D deficiencies in utero may affect immune function and bone development from birth through adulthood. Low birth weight has been associated with low maternal vitamin D levels. And interestingly, the seasonal timing of pregnancy appears to pose an increased future risk for multiple sclerosis in the developing fetus. Because biologically active vitamin D is generated in the skin during exposure to ultraviolet light, the increased risk of multiple sclerosis may be related to seasonal vitamin D deficiency.
The rising prevalence of asthma, especially among African-American children, may also be a sequela of low levels of vitamin D in pregnant women. The rate of vitamin D deficiency in pregnant African-American women has been found to be at least twice as high as that in white women. Autism is another condition with a higher incidence in this population, and although there is no evidence at this time to associate autism with maternal vitamin D deficiency, one author has posed this possibility.
The current recommended requirement for vitamin D during pregnancy (200 IU/d) has little scientific support and is widely believed to be well under the optimal amount. A National Institutes of Health clinical trial is currently underway to evaluate this further. Deficiencies have been prevalent even in studies where over 90% of the women took prenatal vitamins. In the meantime, practitioners might want to consider advising pregnant women, particularly those who receive little sun exposure, to modestly increase their exposure to sunlight, keeping in mind the competing risk for skin cancer. At present, no changes have been made to the recommended daily dose for supplemental vitamin D in pregnant women.

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