Vitamin D Supplements Reverse Deficiency in Pregnant Women

April 18, 2013

By Will Boggs, MD

NEW YORK (Reuters Health) Apr 18 - Vitamin D supplementation in pregnant women increases serum 25(OH)D concentrations without apparent harm to the mothers or their offspring, according to a report of research conducted in Arab women at high risk for vitamin D deficiency.

Low maternal vitamin D, which is associated with poor fetal growth and impaired bone development, is common among Arab and Asian women.

Dr. Adekunle Dawodu from Cincinnati Children's Hospital Medical Center in Ohio and colleagues investigated whether supplementation with vitamin D (400, 2000, or 4000 IU daily) could achieve vitamin D sufficiency in the pregnant women and improve the vitamin D status of their infants at birth, without vitamin D toxicity.

Of 191 women with serum 25(OH)D known at enrollment, only one had a normal level (above 32 ng/mL, or 80 nmol/L), whereas 143 (75%) had levels below 10 ng/mL and 44 (23.2%) had levels between 10 and 20 ng/mL (50 nmol/L), the research team reported April 4 online in The Journal of Clinical Endocrinology & Metabolism.

Vitamin D levels increased from baseline with supplementation, approaching a plateau at week 28 in all groups. Mean serum 25(OH)D levels were significantly higher with 4000 IU daily than with 2000 or 400 IU at week 16 and at delivery. Levels were also significantly higher in the 2000 IU group than in the 400 IU group at both points.

Mean serum 25(OH)D concentrations followed the same pattern in infants: highest in the 4000 IU group, intermediate in the 2000 IU group, and lowest in the 400 IU group.

Mothers in the 4000 IU group were seven times more likely than mothers in the 400 IU group to achieve vitamin D sufficiency. Using the more conservative 20 ng/mL definition, 91% of mothers on 4000 IU had "adequate" levels of 25(OH)D, compared with less than half of mothers on 400 IU.

Similarly, infants of mothers who were on 2000 and 4000 IU daily were two and four times, respectively, more likely to achieve serum 25(OH)D levels of 20 ng/mL, though these levels were still lower than those achieved in a similar randomized trial by U.S. researchers in South Carolina.

Calcium homeostasis did not differ significantly among the mothers in the three groups, and there were no significant differences in the mean birth weight, length, head circumference, and gestational age of their infants.

There were no documented cases of hypervitaminosis D (concentrations above 90 ng/mL) during the study period.

"Vitamin D supplementation of 4000 IU/day in this population appeared to be safe and most effective in achieving vitamin D sufficiency in mothers and serum 25(OH)D 20 ng/mL in infants at birth," the researchers conclude.

"Large randomized controlled trials are needed to test the safety and effectiveness of such supplementation strategy on growth and other nonskeletal health outcomes in the mother and offspring in populations with endemic vitamin D deficiency," they add.

"I believe the aim should be to ensure that women should have 25(OH)D levels of 50 nmol/L or higher, as concluded by the Institute of Medicine in 2010," said Dr. Robyn Lucas from the Australian National University in Canberra, who has published on vitamin D insufficiency in pregnancy, in an email to Reuters Health.

"Although the attached paper noted that 'vitamin D supplementation of 2000 and 4000IU/day appeared safe in pregnancy...' this seems a bold statement when there has been no follow-up of the babies into later life, so that 'safety' cannot be concluded," Dr. Lucas said. "There is some evidence that higher vitamin D levels in utero have adverse effects on allergy in the offspring, i.e. 'safe' needs to be clearly defined."

"Serum 25(OH)D levels should be checked with a precise and accurate assay (standardized to the NIST standard reference measurement protocol) if there are concerns about vitamin D deficiency," Dr. Lucas said. "Management should occur according to the results of these tests."

"Vitamin D supplementation, or advice re sun exposure, will be required for those who are vitamin D deficient," Dr. Lucas concluded. "As far as I am aware, there is no consistent evidence that high 25(OH)D levels are associated with improved pregnancy outcomes."

Dr. Dawodu did not respond to a request for comments on this report.


J Clin Endocrinol Metab 2013.