Higher daily doses of vitamin D lower risk of preterm births: study
A new study found that women taking 4,000 international units of vitamin D daily - 10 to 20 times the dose the leaders of Canada's pregnancy specialists currently recommend - had half the risk of premature delivery than women who took just 400 IU of vitamin D daily.
All pregnant women should take 4,000 international units of vitamin D daily - 10 to 20 times the dose the leaders of Canada's pregnancy specialists currently recommend - to lower their risk of preterm labour, preterm birth and infections concludes the first study to investigate the safety of high doses of vitamin D during pregnancy.
The study found that women in its 4,000-IU-a-day group had half the risk of premature delivery than women who took just 400 IU of vitamin D daily.
Premature birth is the leading cause of newborn deaths in Canada.
And "not a single adverse event" related to vitamin D dosing was found during the study - as U.S. researchers will report Saturday at the annual meeting of the Pediatric Academic Societies in Vancouver.
"We never imagined it would have as far-reaching effects as what we have seen," says lead author Dr. Carol Wagner, a pediatric researcher at the Medical University of South Carolina.
"The message is that all pregnant women should be supplementing with 4,000 IU per day of vitamin D."
The Society of Obstetricians and Gynaecologists of Canada currently recommends pregnant women consume 200 IU/day - and up to 400 IU in their last trimester.
But Dr. Robert Gagnon, chair of the group's maternal fetal medicine committee, says the new study alone is reason enough to support updating those guidelines.
"The concern of giving too much vitamin D in the past was based on wrong studies," says Gagnon, also director of maternal fetal medicine and obstetrics at McGill University and the McGill University Health Centre in Montreal.
For decades, vitamin D was thought to be a teratogen - an agent that cause birth defects - after reports from the U.K. emerged in the 1960s of babies born with heart defects, mental disabilities and elf-like facial features. The babies were found to have high levels of calcium, which doctors attributed to too much vitamin D, since the vitamin helps the body absorb calcium.
What they discovered years later - through genetic technology - was the children had Williams syndrome, a rare disorder caused by deleted genes that affects how babies metabolize vitamin D, leading to higher levels. The conditions weren't a symptom of too much vitamin D but rather a genetic syndrome.
"For 30-plus years it was dogma that (vitamin D in pregnancy) was dangerous, that you didn't need very much and what you did need you could get from just casual sunlight exposure," Wagner said. "What we know now, from a decade of very intensive research, is that that's not the case."
Vitamin D - which in the body acts like a hormone - is important not just for fetal-skeletal health, but also for bone development in childhood, coming a decade later.
Severe deficiencies have been linked to seizures. Others have linked low vitamin D in pregnancy to a higher risk of pre-eclampsia - a sudden increase in blood pressure and protein in urine that can be life-threatening to mothers and babies.
For their study, Wagner and colleagues randomized 494 pregnant women at 12 to 16 weeks gestation into three treatment groups: one group received 400 IU of vitamin D3 a day until delivery; another received 2,000 IU, and the third, 4,000 IU. (Vitamin D3 is better absorbed than D2.)
The higher the dose, the more vitamin D was measured not just in the mother but also in the baby at birth, showing the supplement crosses the placenta to reach the child.
Higher circulating blood levels of vitamin D were associated with lower rates of preterm labour, preterm birth and infection - with the strongest effects were seen in the 4,000-IU-a-day group.
All the women taking part in the study were living in Charleston - in sunny South Carolina. Overall, 85 per cent were either insufficient, or "frankly deficient" in vitamin D when the study began.
"This is the best you can get with lots of sunshine," Wagner said.
"This is even more important for Canadians. You're at a much higher latitude. The best that you can have is probably six months of sunlight exposure, at your lowest latitude, where you can actually make vitamin D," he said. "So you're dependent on your stores."
Even then, when we do go outside, we tend to use sunscreen, which blocks our synthesis of vitamin D.
"If you are marginal during summer months, by the time you get to February and March, what you see is really just horrific deficiency," Wagner said. "What we're trying to do is just get women where they would be if they were out in the field (like) how we evolved, out in the sun-rich environments."
In 2007, the Canadian Paediatric Society began recommending that pregnant and breastfeeding women talk to their doctor about taking 2,000 IU of vitamin D daily, especially during winter.
Health Canada recommends pregnant and nursing mothers consume 200 IU each day, the amount found in two cups (500 mL) of milk or fortified soy beverages.
It remains unclear as to how vitamin D may lower the risk of premature birth. But Gagnon said the vitamin appears to increase the amount of blood flowing to the placenta, bringing more oxygen and nutrients to the baby, and promoting healthier growth.