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Is it safe? · Pregnancy Smart

Vitamin D and fertility: what the evidence says

Assigned clinical reviewerMichael Yuzefovich· MD, FACOGDraft · pending clinical reviewUpdated

What does the evidence say about vitamin D while trying to conceive?

  1. The recommended dietary allowance is 15 micrograms, or 600 IU, a day for adults aged 19 to 70 and the same during pregnancy, with a tolerable upper intake level of 100 micrograms, or 4,000 IU, a day. 1
  2. Blood levels below 30 nmol/L, or 12 ng/mL, are classed as deficiency, 30 to under 50 nmol/L as inadequate, and 50 nmol/L or higher as generally adequate; in 2011 to 2014 data, 18 percent of the United States population aged one and over was at risk of inadequacy. 1
  3. A meta-analysis of 15 cohort studies covering 3,711 women undergoing IVF found that those with sufficient vitamin D, defined as 30 ng/mL or above, had higher live birth rates than deficient women, with an odds ratio of 1.74, while the authors cautioned that demographic and clinical confounders have not been ruled out. 2
  4. Low vitamin D levels in pregnancy have been associated with low birth weight, low infant calcium, and preeclampsia, and deficiency is the main cause of rickets. 3
  5. Whether high or low vitamin D levels affect the chance of birth defects is not known. 3

What to know about vitamin D while trying to conceive

  • The preconception months are the practical time to find out where you actually stand, because correcting a low level takes weeks and a blood test is the only way to know. National survey data put 18 percent of the United States population aged one and over at risk of inadequacy and 5 percent at risk of deficiency, so it is a real possibility rather than a niche one.
  • The recommended amount does not change with pregnancy: 15 micrograms, or 600 IU, a day for adults aged 19 to 70 and in pregnancy alike. Most prenatal vitamins include some vitamin D, so count what you are already getting before adding a standalone product.
  • Stay inside the tolerable upper intake level of 100 micrograms, or 4,000 IU, a day unless your provider is directing a higher dose against a measured level. MotherToBaby notes that low vitamin D has been associated with low birth weight, low infant calcium, and preeclampsia.

Frequently asked questions

Can low vitamin D affect fertility?

The clearest data come from IVF cohorts, where sufficient levels were associated with higher live birth rates than deficient ones. Those are observational studies, so they show a pattern rather than a cause, and the authors flagged that other differences between the groups could explain part of it.

How much vitamin D should I take when trying to conceive?

The recommended dietary allowance is 600 IU a day for adults, unchanged in pregnancy, with an upper limit of 4,000 IU. If a blood test shows you are low, your provider may direct a different amount, which is a different situation from choosing a dose off a shelf.

Should I get my vitamin D level tested before pregnancy?

It is a reasonable thing to ask about, especially since correcting a low level takes time and preconception is when you have it. Whether the test is indicated for you specifically is a clinical judgment, so bring it up at your prepregnancy visit.

Can you take too much vitamin D?

Yes. The tolerable upper intake level for adults is 4,000 IU a day, and NIH flags potential adverse effects at blood levels above 125 nmol/L, or 50 ng/mL. High-dose products sold for correcting deficiency should be taken against a measured level, not on spec.

Related in the library

References

  1. Vitamin D: Health Professional Fact Sheet, NIH Office of Dietary Supplements

    NIH · https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

  3. Vitamin D: MotherToBaby Fact Sheet

    MotherToBaby · https://mothertobaby.org/fact-sheets/vitamin-d/

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.