Vitamin D and fertility: what the evidence says

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.