Vitamin D and Pregnancy
A look at vitamin D intake guidelines for pregnancy
If you’re an obstetrician, you’re probably familiar with the IOM’s most recent recommendations regarding vitamin D for pregnant women. You might also be aware of the Endocrine Society’s recommendations, which are much higher than the IOM’s. And if you’ve been keeping an eye on the latest vitamin D research, you might have come across some of the studies that call for even greater vitamin D supplementation during pregnancy.
If you’re not a healthcare professional and your interest in vitamin D is personal, you might not be aware of these various guidelines. As of the writing of this article, a quick Google search for “vitamin d and pregnancy” returns a plethora of sites hailing the benefits of high-dosage vitamin D supplementation during pregnancy — for cutting the risks of everything from rickets to preeclampsia. These sites don’t prepare you for the conversation with your OBGYN, who may be a lot more cautious about vitamin D supplementation.
Unfortunately, there are a lot of vastly different opinions on vitamin D out there. Let’s take a short look at the guidelines — and why you may want to take them with grain of salt.
To give you an example, the WHO does not recommend any vitamin D supplementation as part of standard prenatal care1. But the “evidence” they used to reach this conclusion is a very small subset of the research conducted on vitamin D — a total of six vitamin D trials were considered.2 All but one trial was performed in the 1980s, despite the influx of research on vitamin D this century.
The IOM, on the other hand, looks at a much more robust body of evidence (though their last recommendation was published before the WHO’s and is similarly missing some important recent research), and they do recommend vitamin D consumption during pregnancy.3 The RDA for vitamin D is 600 IU/day, whether or not you’re pregnant (it’s 800 IU/day for people over 70, and there is no RDA for infants). Though they recognized the existence of good studies suggesting a relationship between vitamin D and preeclampsia, none of the research considered at the time met the stringent requirements of the IOM.
In the same year — 2011 — that the IOM’s revised recommendations came out, the Endocrine Society also published their own clinical guideline on vitamin D.4 They said that the 600 IU/day that the IOM recommended was a minimum for good health, and that individuals “at risk” for vitamin D deficiency should take 1,500 – 2,000 IU/day of vitamin D.
It’s important to note at this point that vitamin D deficiency is not a rare phenomenon. Countless studies have found that large percentages of the population have insufficient vitamin D levels. For example, data from NHANES 2001-2006 lists 33% of the US population at below-sufficient vitamin D levels.5. Even without considering the many sources that suggest the definition of “sufficient” vitamin D levels is too low, that’s a startling percentage of the population at risk of vitamin D deficiency.
A number of randomized controlled trials of vitamin D — the gold standard — have been released since those guidelines were published. We now have multiple modern trials with pregnant women as the subjects, a huge step forward from when the IOM only had one pregnancy trial to consider that wasn’t from the 80s.
In late 2011, a robust randomized controlled trial (RCT) on vitamin D supplementation in pregnancy was published. The study had a significant sample size (350 women continued through delivery) and collected a wide array of data. Trial groups received either 400, 2,000, or 4,000 IU/day of vitamin D3. No trial-related negative outcomes were reported, even for the highest dosage group — something that had been a concern before.
Perhaps the most striking result of this trial was the researchers’ report that the latest IOM recommendations would have raised less than 50% of the subjects’ vitamin D statuses to “sufficient” levels — 50 nmol/L — as defined by the IOM. And that number gets worse with groups at higher risk of vitamin D deficiency, such as dark-skinned women.6
Another RCT supplemented 161 women with either 2,000 IU/day or 4,000 IU/day of vitamin D. The researchers similarly found no adverse effects from high-dosage vitamin D supplementation. Rather, the 4,000 IU group seemed to have benefited from the vitamin D supplementation more than the 2,000 IU group. The 4,000 IU group had a decreased risk of low neonatal weight, higher neonatal vitamin D status, and marginally decreased risk of preterm labor, preterm delivery, and infection.7
A lot more research needs to be done, certainly — but it is incredibly difficult to, for example, perform a good randomized control trial that would clearly illustrate the effects of vitamin D supplementation on pregnancy outcomes such as preeclampsia. Unfortunately, that’s the sort of research that organizations like the IOM require.
In science, it’s hard to say that anything is certain. While there is a large body of evidence to suggest that higher vitamin D intake and higher vitamin D levels are especially important during pregnancy, there isn’t enough proof to convince organizations such as the IOM.
On the other hand, we can probably agree that there is now enough evidence to say that a higher vitamin D intake doesn’t hurt.
With this information in hand, we hope that the decision on vitamin D regimens during pregnancy will be a little bit easier to make.
4 Holick, M. F., Binkley, N. C., Bischoff-Ferrari, H. A., Gordon, C. M., Hanley, D. A., Heaney, R. P., … & Weaver, C. M. (2011). Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. The Journal of Clinical Endocrinology & Metabolism, 96(7), 1911-1930.
6 Hollis, B. W., Johnson, D., Hulsey, T. C., Ebeling, M., & Wagner, C. L. (2011). Vitamin D supplementation during pregnancy: Double‐blind, randomized clinical trial of safety and effectiveness. Journal of bone and mineral research, 26(10), 2341-2357.
7 Wagner, C. L., McNeil, R., Hamilton, S. A., Winkler, J., Cook, C. R., Warner, G., … & Hollis, B. W. (2013). A randomized trial of vitamin D supplementation in 2 community health center networks in South Carolina. American journal of obstetrics and gynecology, 208(2), 137-e1.