TORONTO - Taking high doses of vitamin D during pregnancy is safe and appears to reduce the risk of pre-term birth and infections, say the authors of a study that compared different amounts of supplementation in expectant mothers.
But their recommendation that pregnant women should take 4,000 international units of vitamin D daily -- at least 10 times the standard recommended amount -- is sure to generate controversy.
"When we first proposed the study in 2002, it was heresy to even think about giving more than 400 international units a day of vitamin D," co-principal investigator Dr. Carol Wagner said from Vancouver, where the two-part study is being presented at an international pediatrics meeting.
In the 1950s and '60s, there was concern that vitamin D could cause birth defects, said Wagner, a pediatric researcher at the Medical University of South Carolina in Charleston.
That idea was later debunked and growing evidence has shown that the so-called sunshine vitamin is critical for maternal and infant health, including ensuring strong bones and proper function of the immune system.
"Diet doesn't provide enough vitamin D, and we don't go in the sun as much as we need (to)," said Wagner, adding that her research team set out to determine the optimal dose of vitamin D supplements for pregnant women that would promote health without doing harm.
The researchers enrolled 494 pregnant women at 12 to 16 weeks' gestation in the study and assigned them to three groups: one group received 400 IUs of vitamin D a day until delivery; the second got 2,000 IUs; and the third 4,000 IUs. The women were tested monthly to ensure they were not suffering any negative effects.
Neither the women nor the researchers knew what dose of vitamin D they were receiving in the study, a "blinded," randomized controlled trial whose methodology is considered the gold standard of medical science.
"What we found was that 2,000 was better than 400, and 4,000 was the best, without any adverse events that were associated with vitamin D," said Wagner. "And then ... we found fewer infections in the 4,000 group and fewer pre-term labours and-or pre-term birth deliveries in the 4,000 group compared to the 400 group."
Analysis of the data also showed that the women taking 4,000 units of vitamin D had half the rate of pregnancy-related disorders, such as gestational diabetes and pre-eclampsia, compared to expectant mothers taking 400 units.
"So that blew us away."
However, Wagner conceded that the notion of pregnant women taking a daily dose of 4,000 IUs of vitamin D will likely stir some debate, especially within the medical community. The current recommended daily dose is 200 to 400 IUs daily.
And given the responses of several experts asked to comment on the study, Wagner is right.
Dr. Gideon Koren, head of the Motherisk Program at Toronto's Hospital for Sick Children, said the study is too small to provide such a definitive recommendation and to "declare therapeutic superiority" of 4,000 units of vitamin D.
"I think for now women should be sure that they get the recommended dose. I don't know that this study by itself should send women to buy 4,000. No, no way. I don't think this is sufficient."
"The study's important to show that it doesn't cause side-effects, but I think to tell women that they need 4,000 - to go from 400 to 4,000 - is huge."
However, Dr. Reinhold Vieth, head of the Bone and Mineral Laboratory at Mount Sinai Hospital in Toronto, has long argued that recommended daily amounts (RDAs) for vitamin D are outdated and woefully inadequate.
The Canadian Cancer Society recommends that adults should consider taking 1,000 units a day during the fall and winter. However, older and darker-skinned adults should think about taking that amount year-round.
Vieth, who has conducted numerous studies on vitamin D in different patient populations, said the Canadian Pediatric Society has been advocating 2,000 units during pregnancy since 2007.
"The next step, 4,000, well, I bet you they'll come up with that in a couple of years, because this (the Wagner-group study) has to get published first," he said, adding that he agrees that pregnant women should be taking that level of vitamin D daily.
"Yes, absolutely. They'd be foolish not to."
Dr. Robert Gagnon, a spokesman for the Society of Obstetricians and Gynecologists of Canada (SOGC), said the study was well-designed and its findings are important.
The Montreal specialist said SOGC is in the process of reviewing the medical literature before deciding on its official recommendation for expectant mothers.
"We need to see all the details of the study before we come to the recommendation," he said. "To say (pregnant women) should take 4,000, I think it's a little premature for that."
