Vitamin D plays a significant role in reproductive health for both women and men. Deficiency has been linked to fertility challenges such as PCOS, endometriosis, and reduced IVF success. Ensuring adequate levels before pregnancy may support better outcomes. Here’s what you need to know.

How Does Vitamin D Affect Fertility?

Vitamin D deficiency has been associated with a number of fertility problems, including:

  • PCOS
  • Endometriosis
  • Uterine fibroids
  • Abnormal sperm function
  • Reduced IVF success.

Additionally, low vitamin D levels have been connected to adverse pregnancy outcomes such as:

  • Preterm birth
  • Gestational diabetes
  • Preeclampsia

Vitamin D is also essential for bone health and immune function—both important during pregnancy.

What is a Normal Vitamin D level?

To assess vitamin D levels, a blood test is used to measure 25-hydroxyvitamin D (25-OH D). The Endocrine Society classifies levels as follows:

  • Adequate (replete): 30 ng/ml or greater.
  • Insufficient: 21 to 29 ng/ml.
  • Deficient: below 20 ng/ml

Common Risk Factors for Deficiency

  • Limited sun exposure (e.g., living in the Pacific Northwest)
  • Darker skin tones
  • Aging
  • Obesity
  • Inadequate dietary intake

Note: A newborn’s vitamin D level is largely dependent on the mother’s status during pregnancy.

The current RDA (Recommended Daily Allowance) for vitamin D is 600 IU for adults.

Ideal Vitamin D Levels for Pregnancy and IVF

A recent systemic review and meta-analysis add to our current knowledge on vitamin D status as measured by 25-OH vitamin D and IVF outcomes. In the January 2018 edition of Human Reproduction, eleven previously published studies were analyzed. This review found a high prevalence of vitamin D deficiency with only 25.7% of patients having vitamin D levels above 30 ng/ml. The authors concluded that women who were replete (25-OH vitamin D > 30ng/ml) in vitamin D were more likely to achieve a positive pregnancy test, clinical pregnancy and live birth with IVF.

However, there is no association observed between vitamin D status and miscarriage.
Past studies have shown mixed results. It has been proposed that vitamin D is important for the embryo to be able to successfully implant and develop within the uterus.

Unfortunately, there are no prospective studies demonstrating that Vitamin D supplementation in women or men with insufficient or deficient levels of 25-OH Vitamin D will result in an increase in the live birth rate. Such studies are still needed. Adequate Vitamin D levels during pregnancy may help prevent complications such as fetal growth restriction, preterm labor, pregnancy-related hypertension (pre-eclampsia) and gestational diabetes.

Key Takeaways: Vitamin D & Fertility

  1. Test Early: All women attempting pregnancy should test their 25-OH vitamin D levels.
  2. Aim for 30 ng/mL+: While the optimal fertility level is unclear, >30 ng/mL appears beneficial.
  3. Supplement before pregnancy: This allows time to reach adequate levels during early gestation.
  4. Don’t overdo it: The safe upper limit is likely around 60 ng/mL. Excess vitamin D can be toxic.
  5. It’s safe and affordable: Standard vitamin D3 supplements are widely accessible and low-cost.
  6. Supplement if you’re low: Typical doses are 2,000–4,000 IU of vitamin D3 daily. Vegans can use vitamin D2 or plant-based D3 from lichen.
  7. Be patient: It may take 60–90 days to restore healthy levels.
  8. Take it with food: Vitamin D absorbs best when taken with a fat-containing meal.