Jan. 23, 2012

In 2011, a number of studies identified a connection between low vitamin D levels and an increased risk of gestational diabetes. One of these, published online in Diabetic Medicine in December, was led by Dr. Lorraine Lipscombe, Women’s College scientist and endocrinologist and assistant professor of medicine at the University of Toronto.

“Our study adds to the growing body of evidence calling for a randomized controlled trial to test whether vitamin D supplementation can lower the rate of gestational diabetes,” says Dr. Lipscombe.

A trial would confirm whether vitamin D depletion causes or merely coincides with gestational diabetes mellitus (GDM). It could also show whether vitamin D could reverse or improve GDM in pregnant women.

But even without a trial, Dr. Lipscombe explains, “Studies show that relatively high doses of supplemental vitamin D are both safe and beneficial for Canadians.”

Poorly controlled pre-existing diabetes and GDM are not only unsafe for women, but also increase the risk of macrosomia (big baby syndrome) and future diabetes in babies. Numerous studies have also shown that supplemental vitamin D may prevent or delay the onset of diabetes and reduce complications for those who have already been diagnosed. But since these studies weren’t done in pregnant women, doctors remain cautious in their recommendations.

“Doctors are rightly very careful to avoid harm, so obstetricians and general practitioners still aren’t routinely recommending supplementation to their pregnant patients,” Dr. Lipscombe says.

“But we do know that women who are pregnant and breastfeeding need more vitamin D, and we know that supplementing with 1,000-2,000 IUs a day is very unlikely to be harmful.”

Pregnant women in northern communities in Canada are already counselled to supplement with 2,000 IUs of vitamin D3 each day, yet these recommendations haven’t yet translated to the rest of the country, where office jobs and winter weather often keep people out of the sun and vitamin D-depleted. Vitamin D levels tend to be even lower in people with darker skin – something to consider in multicultural areas.

Dr. Lipscombe suggests that her pregnant patients supplement with 1,000 IUs vitamin D each day, in addition to the 400 IUs in their prenatal multivitamin. It’s a recommendation she would like to see become a best practice.

“When it comes to the evidence around vitamin D, the recommendations are really lagging behind the science.”