The current recommended daily allowance of vitamin D for pregnant women is 600 IU/day.1 Currently, this meager dose of vitamin D is under review, and many articles support a much larger dose for pregnant women. The benefits of higher doses may include: a reduction in gestational diabetes, a reduction in preeclampsia, a decrease in premature births, infants with a reduced risk of rickets and other immune system disorders2, toddlers with a reduced risk of wheeze (a predictor of asthma) by age three3, and improved lumbar spine bone mineral content at age nine.4
These amazing outcomes were discovered in three different studies, the first performed in Charleston, S.C. This study included about 500 women who were in their third or fourth month of pregnancy. The women took 400 IU, 2000 IU, or 4000 IU of vitamin D daily until they delivered. Incidentally, at the start of the study, insufficient levels of vitamin D were seen in 94% of the African-American women, 66% of the Hispanic women, and 50% of the Caucasian women who participated. At the conclusion of the study, when compared with women who took 400 IU of vitamin D daily, those who took 4000 IU were half as likely to develop gestational diabetes or preeclampsia and were less likely to deliver prematurely.2
In another analysis, published in the American Journal of Clinical Nutrition, researchers assessed the maternal intake of vitamin D during pregnancy of 1,194 mother-child pairs. By using a validated food-frequency questionnaire, daily median intake of vitamin D was compared to the primary outcome of wheeze, i.e., a positive asthma predictive index (two or more wheezing attacks among children with a personal diagnosis of eczema or a parental history of asthma) by age three. The lowest mean daily intake levels (356 IU vitamin D) had the highest risk of wheezing. However, the highest mean daily intake levels (724 IU vitamin D) produced the lowest risk of wheezing.3
Finally, in a longitudinal study involving 198 children born in 1991-92, researchers found that children born to mothers with deficient levels of vitamin D (less than 11 ug/L) had significantly lower whole body and lumbar spine bone mineral content by the ninth year, compared with those whose mothers were replete with vitamin D (greater than 20 ug/L). Children whose mothers took vitamin D supplements and those born during the summer months had significantly higher bone mineral content.4
While not yet officially recognized, researchers have expressed opinions on dosing and clinical guidelines. Their current recommendations are to check vitamin D levels at the start of pregnancy and to achieve a 25 hydroxy vitamin D level of at least 40 ng/mL. To achieve this level, a dose of 4000 IU/day starting at 12 weeks gestation is recommended.5
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