There seems to be a lot of excitement around Vitamin D. From its role in supporting the immune system to healthy bones and mood, this supplement is essential for our overall health and wellness.

Vitamin D has also been studied for its role in fertility and pregnancy, and the results are clear:  higher levels of vitamin D are associated with increased fertility rates and decreased miscarriage rates.  I feel very strongly that every woman trying to conceive should know her vitamin D levels so that she can increase her chances of a healthy pregnancy and baby.  Here are a few studies showing higher levels of vitamin D have been associated with:

  • lower rate of miscarriage: every 10 ng/mL increase in vitamin D before conception was associated with a 12 percent lower risk of miscarriage (PMC6109429).  Note that the decreased miscarriage rate was only seen in women with higher vitamin D levels BEFORE becoming pregnant.  Increasing levels DURING pregnancy didn’t improve miscarriage rates, so it’s important to achieve an optimal level BEFORE pregnancy.
  • higher pregnancy rates for women trying to conceive naturally: women who had sufficient vitamin D levels or concentrations of 30 ng/mL or more were 10 percent more likely to become pregnant  (PMC6109429)
  • higher pregnancy rates for women undergoing IVF:  women with higher serum levels had more high-quality embryos and also had higher pregnancy rates (PMC25121462)
  • vitamin D deficiency in pregnancy puts you at a higher risk for preeclampsia, having a lower birth weight baby, gestational diabetes, and postpartum depression.

In addition to the specific pregnancy and fertility research mentioned above, vitamin D has been shown to support our immune system and even decrease menstrual pain (PMC27147120).

  • A 2021 study gave women who had vitamin D levels below 30 ng/mL high dose weekly vitamin D supplementation. After 8 weeks, the vitamin D group showed a significant decrease in menstrual pain intensity versus the placebo group. There were even improvements in other PMS symptoms in the vitamin D group, including headache severity and diarrhea with no significant change in the placebo group (PMC8290151).

Vitamin D can be a safe, easy, inexpensive supplement to add to our daily routine.

So how much Vitamin D do we need?
Unfortunately, it’s not a simple one-size-fits-all answer.  We need to start with knowing our own levels and look at what the research shows about “optimal” levels.   Then, we can discuss what studies have shown are safe levels to supplement.

Optimal Vitamin D levels
If I could give women trying to conceive ONE piece of advice it would be this:  KNOW YOUR VITAMIN D LEVEL!  #knowyourvitaminDlevel (not very catchy is it?).  By the way, in addition to checking Vitamin D levels with my fertility clients, this is the first thing I check when working with a woman who has painful periods because of the research showing decreased menstrual cramps with adequate levels.

Most labs test for 25-OH Vitamin D (25-hydroxy vitamin D) and use 30 ng/ml as the cut-off for normal. Research suggests 30-40 ng/mL levels may be optimal for fertility. Many health experts advocate for higher levels in the 40-60 ng/mL range, but the data doesn’t support higher levels being better. You can ask your doctor for a lab order to check your level (it may or may not be covered by your insurance), or you can order a home kit from Let’s Get Checked for $89 (I have no relationship or affiliation with this company. I have used their test personally and loved how convenient it was to do a fingerstick at home).

Supplementation Safety and Dosage
A 2011 study found that supplementation of 4,000 IU/day for pregnant women was safe and most effective in achieving sufficiency in all women and their neonates regardless of race while the current average requirement (400 IU – 2,000 IU per day) was comparatively ineffective at achieving adequate vitamin D levels, especially in African Americans. (PMC3183324)

Another 3-year study published in 2020 looked at the safety profile of vitamin D supplementation in the following doses:  400 IU per day, 4,000 IU per day, and 10,000 IU per day.  In this study, there were no adverse effects reported for the intake of vitamin D up to 10,000 IU per day (I am NOT suggesting anyone take up to 10,000 IU per day). (PMD26035242)

I think it is important to know your vitamin D level and then supplement accordingly.

Talk to your doctor or healthcare professional about testing your vitamin D levels so you know if you are deficient, “lab normal”, or optimal and consider adding an inexpensive vitamin D3 supplement to move into the optimal range.  You should always work with a healthcare practitioner to assess what is right for you.

One of my favorite, high-quality vitamin D3 supplement brands is Carlson.  You can see all of my favorite prenatal supplement brands on Fullscript here.


There are things you can do now to optimize your fertility and be in the best health possible when this is all over.

That’s why I created 5 Simple Changes You Can Do Today To Improve Your Fertility.

These simple, yet powerful, steps are the foundation for healthy fertility.

They are also part of the preconception plan that I put every client on when we start working together.

They are the top five things I wish every woman (and her partner!) would start doing before they even begin trying to conceive.

You can download it from the link here

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