Twenty-five percent of all deaths of pregnant women are due to pre-eclampsia, an inflammatory disorder that presents with high blood pressure and protein in the urine. If you are pregnant, your risk of getting pre-eclampsia is about 5%. It can lead to eclampsia, an acute and life-threatening emergency of pregnancy characterized by seizures.
To date two small studies have found lower vitamin D levels are associated with higher risk of pre-eclampsia and several additional small studies have found little doses of vitamin D (400-600 IU/day) reduce the risk of pre-eclampsia a little. Now, just recently, we have a prospective (looking forward) cohort (group) study of a large number of women from many different hospitals to see if vitamin D levels are associated with pre-eclampsia.
Dr. Shu Qin Wei and colleagues from seventeen urban hospitals in Canada, including the University of Montreal, followed 697 women, 32 of whom developed pre-eclampsia. The authors measured vitamin D levels in all the women on two occasions during their pregnancy, once in the first trimester and again in the third trimester. They discovered that women with levels less than 20 ng/ml on their second draw were three times more likely to get the disease.
They found an inverse association with the curve showing that your chance of pre-eclampsia is about 12% if your vitamin D level in 5 ng/ml and the risk is about 0% if your vitamin D level is 50 ng/ml. The associations were only seen in the second blood draw, not the first one. Furthermore, there was a tendency for women who developed pre-eclampsia to have falling vitamin D levels in their pregnancy. That is, their first vitamin D test was higher than their second one. The authors (and me) have no explanation for that finding, other than falling vitamin D levels in pregnancy are bad, as are low levels.
Disappointingly, the authors called for more epidemiological studies before any randomized controlled trials. Fortunately, there are three randomized controlled trials in the works that are examining this very topic, either as a primary or secondary outcome.
Even more disappointing, the authors did not call for treatment of vitamin D deficiency during pregnancy. In my opinion, based on their data, I would rather have women sufficient in vitamin D in the mean time, until a randomized controlled trial gives us more data. On that note, the Vitamin D Council recommends pregnant and soon-to-be-pregnant women take at least 5,000 IU day on days you do not receive sufficient sun exposure. As the baby grows, say beginning the third trimester, increase the dose to 6,000 IU/day, 5,000 for mom and 1,000 IU for baby.