If you are a woman with low vitamin D levels, taking a supplement of this key vitamin may increase your ability to get pregnant and carry the baby to term. That’s why many fertility practices routinely screen for vitamin D levels and give supplements to women who are deficient.
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But if some vitamin D is good, more is not better. The results of a recent study suggest that too much vitamin D actually may be harmful.
“There appears to be a sweet spot in a U-shaped curve,” says fertility specialist Rebecca Flyckt, MD. “Oversupplementation may be as disadvantageous as deficiency.”
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New twist on an old theme
In the study, presented at the European Calcified Tissue Society meeting in May, researchers gave two different amounts of vitamin D or placebo to 193 women with naturally low levels of the vitamin who were planning to start a family. A total of 108 became pregnant within 12 months.
About the same percentage of women who took the lower dose of vitamin D (1400 IU) or the placebo became pregnant. Those who took the higher dose (2800 IU), however, were half as likely to conceive as those who took placebo.
New benefits revealed
Vitamin D did appear to have one significant benefit. Those who took the vitamin had fewer complications such as preeclampsia and postpartum bleeding than those who took placebo. In fact, complications during labor were significantly more common among those who did not take vitamin D supplements.
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What should a woman do?
Vitamin D deficiency is very common, particularly in Northern climes where the sun is weak and summer is short. Since too little vitamin D can cause brittle bones, many fertility specialists test female patients for vitamin D and prescribe supplements, if needed. Doses may be initially high—up to 4000 IUs—but are usually reduced when recommended blood levels of the vitamin are reached.
While the role of insufficient vitamin D in conception and healthy pregnancy is accepted, the role of too much vitamin D is still unclear. According to Dr. Flyckt, this study raised more questions than answers.
“This was a very small study, with only 31 to 41 pregnant women in each group. You really need bigger numbers to draw meaningful conclusions,” she says.
Until more is known, she says the take-home message is that you need to be judicious. She recommends a daily dose of 1000 IU or less for women planning to conceive.
“Vitamin D supplementation may have benefits, but too much of a good thing may not be a good thing,” she says.