Vitamin D and Fertility: The Underrated Factor

There is one nutrient that shows up low in a striking number of the women I work with. A nutrient that can touch fertility on several different levels, and yet one that almost never comes up in a standard fertility workup.

I'm talking about vitamin D. And when I say it rarely comes up, I mean that quite literally. Most of the women who come to me have no idea where their vitamin D level actually sits, let alone whether it's in a place that genuinely supports trying to conceive.

I'm Melissa Schemionek, and as a holistic fertility and hormone coach here in Austin, vitamin D is one of the first things I like to look at, in partnership with a woman's doctor. Not because it's the single answer to everything, but because it's so often a quietly missing piece of the puzzle.

Vitamin D Is Really More of a Hormone

Here's something that surprises a lot of women: vitamin D isn't truly a vitamin in the classic sense at all. It behaves much more like a prohormone, a precursor your body can actually produce on its own, primarily through sunlight on the skin.

The catch is that modern life works against us. Many of us spend our days indoors, under artificial light, behind windows, and reasonably wearing sunscreen when we are outside. Depending on where you live and the time of year, the sun simply may not be strong enough for long stretches to help your body make what it needs. The result is that suboptimal vitamin D levels are remarkably common, and the demand can climb even higher in the season of preparing the body for pregnancy.

How Vitamin D Can Influence Your Fertility

What makes this nutrient so interesting is its reach. Vitamin D receptors show up in tissue throughout the body, including the ovaries, the uterus, and the placenta. Research continues to point to just how layered its influence on fertility may be:

• Egg quality. Vitamin D appears to play a role in the maturation of eggs and may be part of what supports egg quality over time.
• Hormone production. It's involved in the production of estrogen and progesterone, two of the central hormones in the conversation about conception.
• Implantation. Vitamin D may influence the receptivity of the uterine lining, which is part of what shapes the conditions for implantation.
• Immune regulation. It helps modulate the immune system, which can be especially relevant in conversations around recurrent loss.
• Insulin sensitivity. Vitamin D is tied to insulin sensitivity, which can matter a great deal for women navigating PCOS.
• Ovarian reserve markers. Some research has explored a possible link between vitamin D and AMH, a marker often used to talk about ovarian reserve.

And this isn't only a woman's story. Vitamin D may also play a part in sperm quality, including motility and morphology, which is a good reminder that fertility is something a couple holds together.

What the Research Is Pointing Toward

The picture emerging from the research keeps getting clearer. Studies have observed associations between healthier vitamin D status and outcomes that matter to women trying to conceive, including in the context of fertility treatment. Lower levels, on the other hand, have been linked in some research to a higher risk of loss. Among women with PCOS, vitamin D has been studied in relation to cycle regularity, and women with endometriosis are often found to have lower levels.

Of course, research is never the whole story, and vitamin D is not a stand-alone fix for fertility challenges. But the signal is consistent enough that I feel comfortable saying this: leaving a vitamin D deficiency unexamined while trying to conceive is a missed opportunity, and often an easily corrected one.

Why Your Doctor May Not Have Tested It

Vitamin D is often left out of routine testing, so for many women it simply never gets measured unless someone specifically asks for it. And even when it is measured, it's frequently judged against a reference range that was never designed with conception in mind.

This is the part I most want you to sit with. The level that gets labeled "normal" or "sufficient" on a standard lab report is not necessarily the level that best supports fertility. There is a meaningful difference between simply avoiding a deficiency and reaching a place that genuinely supports your body's work of preparing for pregnancy. There is a better target for this season of life, one that sits above what many labs flag as adequate. Where exactly that target lands, and what it would take for you to reach it, is deeply individual. It depends on your current level, your body, your skin, the time of year, and anything else going on with your health, which is why the specific number is something I prefer to walk through personally on a discovery call rather than hand out as a one-size-fits-all figure on a page.

It's worth naming why this matters. A standard panel can read as perfectly "normal" and still miss things that quietly shape fertility, which is something I see again and again with routine bloodwork. Vitamin D is one of the clearest examples.

Why You Shouldn't Just Start Supplementing on a Hunch

I can almost hear the thought forming: "Then I'll just grab some vitamin D off the shelf and be done with it." And gently, that's exactly the instinct I'd ask you to pause on.

Vitamin D is fat-soluble, which means your body stores it. Unlike water-soluble vitamins that you simply flush out, vitamin D can build up, and it is genuinely possible to take too much. Over-supplementing isn't a harmless experiment, which is one of the reasons this belongs under medical guidance rather than guesswork.

There's also a subtler issue. Vitamin D doesn't work in isolation. It relies on other nutrients, its cofactors, to be used well in the body. Without them, supplementing can be far less effective, and the amount that's right for one woman can be wrong for another.

So the thoughtful path looks less like grabbing a bottle and more like a sequence: first understand where your level actually is, then determine the right amount for you alongside your doctor, and then check back to see whether things are moving in the right direction. It isn't complicated, but it does deserve to be done with intention rather than by accident.

Vitamin D When You're Considering IVF

If you're thinking about IVF or already in the middle of treatment, attending to your vitamin D status is one of the simpler, more meaningful steps you can take in the lead-up to a transfer. It tends to be low-effort and high-value, the kind of foundational piece that's easy to put in place while so much else feels out of your hands.

Because eggs mature over a window of roughly ninety days, you have a real opportunity to shape the conditions your eggs are developing in, and vitamin D is part of those conditions. That window is one of the most hopeful things I get to share with women, because it means today's choices are quietly working on your behalf.

One Nutrient Inside a Larger Whole

Vitamin D matters. And it is one instrument in a much larger orchestra. It works alongside the other nutrients that fertility relies on, and these pieces influence one another, sometimes amplifying, sometimes competing. That's exactly why optimizing a single number in isolation rarely tells the full story. Your body works as a system, and it deserves to be seen that way.

Which nutrients deserve priority in your particular case, how they interact, and what the right amounts are for you is as individual as a fingerprint. It's also why I never lead with blanket recommendations, but with a picture built around your own values and your own body.

If you've been quietly wondering whether your vitamin D is truly where it needs to be for conception, that wondering is worth honoring. You don't have to figure it out from a label or a late-night search. Every cycle carries hope, and an unexamined gap is simply one less unknown standing between you and the family you're building toward. When you're ready to look at your own picture together, I'm here.