What should I know about vitamin D?
The short answer
Women with healthy vitamin D levels tend to have better IVF results. Whether correcting a low level improves them is a different question, and hasn't been shown.
What to know
- The practical move is to measure your level rather than guess at a dose.
- Vitamin D status tracks with sunlight, body composition and general health, any of which could carry the effect.
- Correcting a real deficiency is worth doing for your general health regardless.
- It builds up in the body, so high doses without a measured level aren't advisable.
Read the full explanation
What to do
- Most prenatals include vitamin D. The recommended amount in pregnancy is 600 IU a day, and the safe upper limit is 4,000 IU.
- Testing isn't routine. The Endocrine Society (2024) advises against routinely testing vitamin D in pregnancy, and ACOG suggests testing people at higher risk of deficiency — for example if you get little sun, have darker skin, or eat a vegetarian diet. If that's you, ask.
- If you're deficient, 1,000–2,000 IU a day is generally considered safe; your doctor may suggest more for a short time.
- What the numbers mean: a blood level of 20 ng/mL (50 nmol/L) or higher is adequate for most people; below 12 ng/mL is deficient.
Be careful
Safety consideration Don't go over 4,000 IU a day without supervision. Vitamin D interacts with some medications, including steroids, thiazide diuretics, statins and orlistat.
What the evidence is based on
Almost entirely IVF. An analysis of 11 studies of about 2,700 women found those with sufficient vitamin D had more live births than those who were low. But every one of those studies observed levels rather than assigning supplements, and trials of supplementing before IVF are few and mixed. If you're trying naturally: correct a deficiency, but there's no evidence that extra vitamin D beyond that boosts fertility.
What the research shows
Is vitamin D status associated with assisted reproduction outcomes, and does correcting a deficiency help?
Studies disagree, or the answer changes depending on the situation.
Who was studied. Women undergoing ART, in observational studies comparing those replete, insufficient and deficient.
Outcome measured. Clinical pregnancy
What was found. Women who are vitamin D replete have better ART outcomes in observational data. Whether correcting a deficiency improves those outcomes is a different question, and it has not been convincingly demonstrated.
Main limitation. Observational only — vitamin D status tracks with sunlight, body composition and general health.
Why this rating?
The association is reasonably consistent, but association is not the same as benefit from treatment - vitamin D status also tracks with sunlight, body composition, diet and general health, any of which could carry the effect. Rated low, and deliberately split into two questions.
Questions for your doctor
Edit any of these before you add it — they're yours. Your list stays in this browser, and you can print a one-page sheet from it.
- Can we check my vitamin D level, and what would you do if it's low?
- When would we re-check it?
Sources
- NIH Office of Dietary Supplements, Vitamin D fact sheet
- Endocrine Society, Vitamin D for the prevention of disease (2024 guideline)
- Chu et al., Vitamin D and ART outcome: systematic review and meta-analysis, Human Reproduction 2018
- NIH Office of Dietary Supplements, Dietary supplements in pregnancy