Vitamin D in pregnancy is one of those topics that sounds simple, but the details really matter. You use this essential vitamin in nearly every part of your body, and your baby depends entirely on you to supply it. The problem is that most pregnant moms do not get enough. Deficiency is incredibly common, and it is linked to a higher risk of complications like preeclampsia. To make things more confusing, most prenatal vitamins contain far less vitamin D than the evidence suggests you need during pregnancy. In this episode, we break down what vitamin D actually does, why deficiency is so widespread, how much you really need, and the simplest ways to make sure you and your baby are getting enough.

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What is Vitamin D?

Vitamin D is a fat-soluble vitamin, which means it dissolves in fat and is stored in fatty tissue. As a result, your body can hold on to it and use it as needed. This is different from water-soluble vitamins, which your body flushes out when you have extra.

One of the most important jobs vitamin D does is help you absorb other essential nutrients. This includes calcium, iron, magnesium, phosphate, and zinc. In addition, vitamin D regulates immune function, supports cell growth and neuromuscular function, and affects thousands of genes. You actually have receptors for vitamin D throughout your body, including the placenta, breast, colon, lung, bone, pancreas, immune system, and the lining of your blood vessels. This is not a nutrient that does just one thing.

Types of Vitamin D

There are two main types of vitamin D. D3 (cholecalciferol) is generated in your skin and in the skin of animals. D2 (ergocalciferol) comes from plants. Both forms start out biologically inert, which means they are not yet active. We get this inactive vitamin D from sun exposure, food, and supplements.

To become useful, vitamin D has to go through two conversion steps in the body. The first happens in the liver, which converts vitamin D to calcidiol. The second happens mostly in the kidneys, which form calcitriol. Calcitriol is the active form. This is also why vitamin D is sometimes called a hormone, because the activated forms function as hormones in the body.

Why Vitamin D Deficiency Is So Common

Our modern lifestyles have dramatically changed how much vitamin D we get naturally. Our ancestors spent far more time outside, and those who lived in colder climates far from the equator ate diets rich in fish. Today, the picture looks very different. We spend most of our time indoors, many of us live where sunlight is limited for part or most of the year, we wear sunscreen that blocks the rays we need, and our diets are not rich in vitamin D. As a result, deficiency is more common than ever. An estimated 1 billion people worldwide are deficient in vitamin D, across all ethnicities and age groups.

The most serious risks of deficiency are rickets in children and osteoporosis in adults. Rickets causes softening and distortion of the bones, while osteoporosis makes bones brittle and prone to fractures. Because of this, many developed countries started fortifying foods with vitamin D in the 1930s to reduce rickets. Since then, researchers have linked low vitamin D to a wide range of conditions, from cancer to COVID-19. Given how many processes in the body rely on vitamin D, it makes sense that a deficiency could affect a wide range of health outcomes.

Some groups are at higher risk of deficiency than others. Older adults are more vulnerable because skin converts vitamin D less efficiently with age. People with limited sun exposure, whether because of where they live or how they spend their days, are also at greater risk. The same is true for anyone who covers most of their skin with clothing or is diligent about sunscreen. Under ideal lab conditions, applied at the thickness used in testing, sunscreen with an SPF of 15 can block most vitamin D production in the skin. In real-world use, though, the effect tends to be smaller, because most people apply far less sunscreen than that and miss spots.

Skin tone matters too. People with more melanin in their skin produce less vitamin D, so people with darker skin tones are at higher risk of deficiency. People with obesity also tend to have lower available vitamin D, because fat cells hold on to it and make it less available to the rest of the body. Finally, certain conditions that affect fat absorption, along with some genetic differences in how we convert vitamin D, can raise the risk as well.

The only way to know for sure is a blood test that measures the serum level of 25-hydroxyvitamin D, abbreviated as 25(OH)D. This marker rises and falls in proportion to how much vitamin D you make and take in. Unfortunately, most doctors do not routinely screen for it. This is especially relevant during pregnancy, because many expecting mothers are deficient. One study of vitamin D during pregnancy found that 97% of African American women, 81% of Hispanic women, and 67% of Caucasian women were deficient.

Why Vitamin D Matters in Pregnancy

During pregnancy, your baby relies entirely on your vitamin D levels for their supply. The main job of vitamin D is helping your body absorb calcium from your food. Without enough vitamin D, you only absorb a fraction of the calcium you take in. Calcitriol, the active form, is naturally elevated during pregnancy so that you can deliver enough calcium to your growing baby. An estimated 25 to 30 grams of calcium transfer to your baby’s skeleton by the time they are born, and most of that happens in the last trimester. This is why vitamin D becomes especially important as your baby’s bones develop.

Of course, your baby needs vitamin D for far more than bones. Deficiency in pregnancy is a risk factor for preeclampsia, and it is also associated with increased odds of a primary cesarean section. The effects may reach well beyond birth, too. One study looked at how maternal vitamin D deficiency could affect a child later in life. Researchers found associations with impaired lung development at age six, neurocognitive difficulties at age ten, a higher risk of eating disorders in adolescence, and lower peak bone mass at age twenty. The bottom line is that the evidence strongly supports making sure you get enough vitamin D during pregnancy.

How Much Vitamin D Do You Need?

To understand how much vitamin D you need, it helps to know that there are two different numbers in play. The first is your measured 25(OH)D blood level, which tells you where you actually stand. The second is the amount of vitamin D you take in each day. These two things are related, but they are not the same.

Let’s start with blood levels. The National Academy of Medicine set reference points for serum 25(OH)D concentrations. A level below 30 nanomoles per liter, or 12 nanograms per milliliter, is considered deficient. Between 30 and 50 nanomoles per liter, which is 12 to 20 nanograms per milliliter, is inadequate for bone and overall health. Above 50 nanomoles per liter, or 20 nanograms per milliliter, is considered adequate for most healthy people, and levels above 125 nanomoles per liter, or 50 nanograms per milliliter, may be associated with potential harm. The catch is that the only way to know your number is to get tested.

Now let’s talk about daily intake. Recommended amounts are set in the Dietary Reference Intakes, which vary by age, sex, and whether you are pregnant or breastfeeding. There are two key values. The Recommended Dietary Allowance, or RDA, is the daily intake that meets the needs of nearly all healthy people. The Tolerable Upper Intake Level, or UL, is the most you can take daily without likely harm. For vitamin D, the recommendations are actually the same from age one to seventy, whether you are female, pregnant, or breastfeeding. The RDA is 15 mcg (600 IU), and the UL is 100 mcg (4,000 IU).

Confused yet? Vitamin D is listed two ways on labels, in micrograms (mcg) and in international units (IU), and they are not the same number. To convert, 1 mcg equals 40 IU. So 25 mcg is 1,000 IU, 50 mcg is 2,000 IU, and 100 mcg is 4,000 IU. If your bottle only lists mcg, just multiply by 40 to get the IU figure, since IU is what most of the pregnancy research uses.

Here is where it gets interesting, because some professional societies take a stronger position. In 2024, the Endocrine Society published a new guideline that updates and replaces its older recommendations. For pregnancy, the panel now recommends vitamin D supplementation for everyone, rather than waiting for a blood test to show deficiency. They point to the potential to lower the risk of preeclampsia, preterm birth, a baby who is small for gestational age, and pregnancy loss.

Getting an adequate amount is one thing, but you really want not just an adequate level but an optimal one. This new guideline also gives more direction on dosing. Across the trials they reviewed, the vitamin D doses ranged from 600 to 5,000 IU per day, with a weighted average of roughly 2,500 IU per day. This guideline also suggests against routine vitamin D testing in healthy pregnant women, because there is not yet a clear blood-level target that reliably predicts better pregnancy outcomes. The takeaway is that the current thinking leans toward simply supplementing rather than testing first.

So how should you think about all of this? The RDA sets a floor of 600 IU. The evidence, including the latest Endocrine Society guidance, supports going well above that during pregnancy, often in the range of 1,000 to 4,000 IU per day. It is worth being clear about what that 4,000 IU figure is, though. This is the National Academy of Medicine’s official upper limit, meaning the most they consider safe for nearly everyone without medical supervision. It is a deliberately conservative number, and other expert groups set the ceiling higher. The Endocrine Society, for example, has used 10,000 IU per day as its upper limit. So 4,000 IU is a safe target to aim for, not a hard line where risk suddenly begins.

Can You Get Too Much Vitamin D?

Most vitamins are water-soluble, so if you take too much, your body simply passes the excess in your urine. Only four vitamins are fat-soluble: A, D, E, and K. Since your body stores these in fat rather than flushing them out, they carry a higher risk of building up to toxic levels.

Here is the reassuring part. You cannot get too much vitamin D from sunlight, though you can certainly get a sunburn, so you should still protect your skin. You can, however, take too much in supplement form. Toxicity is usually the result of an accidental overdose or an error in manufacturing. In the 1990s, for example, a dairy made a processing error that left a batch of milk with about 58,000 IU in just 8 ounces, and the mistake only came to light after eight people were hospitalized.

When toxicity occurs, it leads to hypercalcemia, a buildup of calcium in the blood that disrupts bone metabolism. The good news is that it is usually treatable without lasting harm. It also helps to understand how toxicity actually develops. It is not about a single big dose on one day. Instead, vitamin D toxicity generally comes from taking very high amounts day after day over weeks, months, or even years. Acute toxicity is typically associated with sustained intakes above 10,000 IU per day, far beyond the 600 IU RDA and the amounts used in pregnancy. So if you accidentally doubled up one day, that is not the concern. The concern is consistently taking far more than you need over a long stretch of time.

What the Pregnancy Research Says About Dosing

Let’s look at the evidence specific to pregnancy. A double-blind randomized clinical trial assigned pregnant women to receive 400, 2,000, or 4,000 IU of D3 per day from weeks 12 to 16 and continued until birth. The researchers found that 4,000 IU per day was both safe and the most effective at achieving sufficiency in the mothers and their newborns, regardless of race. The lower doses, like the 400 IU found in a typical prenatal, were far less effective at reaching adequate levels, especially in African American women. A separate randomized controlled trial reached a similar conclusion, supporting 4,000 IU per day during pregnancy.

A Cochrane Review synthesized this by comparing women who took vitamin D during pregnancy with those who received a placebo or no supplement. This review was updated in 2024 and looked at eight studies involving 2,313 women. The takeaway is more cautious than you might expect. The evidence on whether vitamin D lowers the risk of preeclampsia, gestational diabetes, or preterm birth was very uncertain, largely because the available studies are small and of mixed quality. There was some low-certainty evidence that supplementing may reduce the risk of severe postpartum hemorrhage, but that came from a single study. The reviewers concluded that we need larger, higher-quality trials to say anything definitive, especially when it comes to safety.

It is worth pausing on the apparent tension here. The Endocrine Society leans toward supplementing during pregnancy, while this Cochrane review is more reserved about the proof of specific benefits. Both of these can be true at once. The Endocrine Society weighs the low cost and low risk of supplementing against the potential upside, even where the trial evidence is not yet definitive.

It is worth noting where the more cautious guidance lands. The American College of Obstetricians and Gynecologists does not recommend routine vitamin D supplementation beyond what is in a prenatal vitamin, and it does not support routine testing of vitamin D levels. That said, ACOG does note that when deficiency is identified during pregnancy, most experts agree that 1,000 to 2,000 IU per day is safe. So while ACOG is more conservative than the Endocrine Society, both agree that supplementing within these ranges is reasonable and safe.

So here is the research in a nutshell. Deficiency is common and clearly worth avoiding, and supplementing during pregnancy appears safe at the doses studied. Given the low cost and low risk, expert guidance like the Endocrine Society still leans toward supplementing, with reasonable amounts landing somewhere between 1,000 and 4,000 IU per day. The bigger debate is less about whether to supplement and more about how much.

Where Your Vitamin D Comes From

There are really only two ways your body gets vitamin D: from the sun or from your diet, including supplements. Let’s walk through each one so you can get a realistic sense of how much you are actually getting.

Vitamin D From Sunlight

It is estimated that about 90% of our vitamin D comes from the sun. And because vitamin D is fat-soluble, your body can store it. This means you can build up reserves during the summer months, when you typically get more sun exposure, and draw on them later.

The sun gives off both UVA and UVB rays. UVA rays contribute to skin damage and premature aging, while UVB rays are the ones your body needs to make vitamin D. When UVB rays hit your skin, they kick off the conversion process. Your skin initiates the reaction, and then your liver and kidneys play a role, effectively converting sunlight into the active hormone your body can use.

How much vitamin D you actually make depends on many factors, including where you live, the season, the time of day, how much skin you expose, and your skin tone. If you live near the equator, you get more usable sunlight year-round. If you live above 37 degrees latitude, you probably are not making enough vitamin D from the sun during the winter. To picture that line, imagine cutting California in half around San Francisco and tracing across the northern borders of Arizona, New Mexico, and Texas, over to Philadelphia on the East Coast.

There are a couple of other things worth knowing. UVB rays do not pass through glass, but UVA rays do. That means if you sit by a sunny window, you can still get sun damage without making any vitamin D. Sunscreen works the same way for vitamin D production. SPF blocks UVB rays, and broad-spectrum sunscreen blocks both UVA and UVB, so any sunscreen with SPF will limit how much vitamin D you make.

Pregnancy adds another consideration. Your skin tends to be more sensitive when you are pregnant, including to the sun. If you have melasma, which is darker patches of skin on the face, or other pregnancy-related pigmentation changes like a darkening line down your belly, sun exposure can make them more noticeable. The same goes for stretch marks. Fresh stretch marks contain little to no melanin, so they do not tan the way the surrounding skin does. Sun exposure can darken the skin around them and make them stand out more, and it can slow how they fade over time. If you are spending time in the sun, it is worth keeping these areas covered or protected.

Reliable guidelines on exactly how much sun you need for vitamin D are hard to find. This is partly because so many variables are involved and partly because you cannot know your levels without a test. There are plenty of online calculators, but they vary widely, and I could not find good evidence that they are accurate.

There are a few general rules that are helpful. The strongest UV light is between 10:00 am and 2:00 pm. Spending an hour outside at 9:00 am gives you about the same UV exposure as 15 minutes at 1:00 pm. As a rule of thumb, if you are out long enough for your skin to turn pink, you have stayed out too long. You do not need to be out in the sun for hours or expose much skin. Getting some sun on your arms, legs, face, or back is enough. For many people, though, it is simply not realistic to rely on the sun year-round, and that is where diet and supplements come in.

Vitamin D From Your Diet

Getting enough vitamin D from food alone is genuinely difficult. Fish is one of the richest food sources. A 3-ounce serving of wild-caught salmon has about 570 IU, though farmed salmon has roughly a quarter of that. If you are buying salmon for the vitamin D, steer clear of Atlantic salmon, which is farm-raised, or look for fish specifically labeled wild-caught. Fish oil is also high in vitamin D, and some fish oil supplements include it.

Beyond that, many foods are fortified, so an 8-ounce glass of milk or fortified orange juice has around 120 IU. Unless you eat fish every day or drink a lot of milk, it is unlikely you are getting enough vitamin D from your diet alone. Most other foods contain only small amounts. A single egg yolk, for instance, has about 44 IU, so you would have to eat more than a dozen eggs a day just to hit the 600 IU RDA.

A plant-based diet makes it even harder to get vitamin D from food. The main whole-food plant source is mushrooms, but only those treated with UV light or grown in the wild. Most grocery-store mushrooms, like white button mushrooms, grow in dark rooms and contain very little vitamin D. If you want to increase your consumption of mushrooms as a source of vitamin D, look for ones specifically exposed to sunlight or UV lamps. Keep in mind that vitamin D levels start dropping after about a week in the fridge, and cooking reduces them further. For a deeper dive, you can read this review on mushrooms as a vitamin D source.

Beyond mushrooms, plant-based options are mostly fortified foods, like fortified plant milks, orange juice, and cereals, along with supplements. For supplements, look for vegan D3 made from lichen, since most D3 is animal-derived and D2 from plants is generally considered less effective at raising your levels.

Vitamin D in Your Prenatal Vitamin

Most prenatal vitamins contain 400 IU of vitamin D, which we now know is likely not enough during pregnancy. Some higher-quality options, like the Zahler Prenatal +DHA, include more to reflect the evidence that 400 IU falls short. It is worth reading the label yourself so you know exactly how much you are getting before you decide whether to add a separate supplement.

Taking a Vitamin D Supplement

For most people, the simplest approach is the one the Endocrine Society now points to during pregnancy, which is to skip routine testing and just supplement. That removes a lot of the guesswork. From there, you can always talk to your doctor or midwife about a test if you want a clearer picture, especially if you are in a higher-risk group. I would also take into account how much vitamin D is already in your prenatal vitamin, in any other supplements you take, and in your diet, so you have a rough sense of your total before adding more. As with any supplement, run your plan by your doctor or midwife first.

Vitamin D supplements come in several different forms, and they are relatively inexpensive. As with any vitamin or supplement, quality matters. A study published in JAMA Internal Medicine tested 55 bottles of vitamin D from 12 manufacturers and found the actual content ranged widely, from 9% to 146% of what the label claimed. The amount even varied from pill to pill within the same bottle.

You will also notice that some D3 supplements include K2. The role of vitamin K here is to help direct the calcium that vitamin D helps absorb into your bones, rather than letting it accumulate in your arteries. Personally, I take a supplement that combines D3 with K2. If you would like to try one, when you first subscribe to AG1, you get a bottle of their D3 plus K2 with your order. It is a liquid, so you just use the dropper and add it to a drink or take it straight, which makes it easy to adjust your dose.

Vitamin D and Your Baby After Birth

Your baby depends on you for vitamin D in the womb, and that dependence continues after birth when they are breastfeeding. Remember, vitamin D can be stored, and most infants use up the vitamin D they got from you before birth by around eight weeks of age. For the first six months, your baby’s diet is entirely breastmilk or formula. Breastmilk is naturally low in vitamin D, while infant formula is fortified with it. On top of that, doctors recommend keeping babies out of direct sunlight for the first six months, which removes the other main source.

It is worth understanding why breastmilk is low in vitamin D, because it is not a flaw in breastmilk. The amount of vitamin D in your milk closely tracks the level in your own blood. Most mothers today run low, mainly from limited sun exposure and low dietary intake, so their milk runs low too. A mother with healthy vitamin D levels actually produces milk with more of it.

Given all of this, in 2009 the American Academy of Pediatrics doubled its recommended intake for children to at least 400 IU per day. The AAP advises that infants who are exclusively or partially breastfed receive 400 IU of supplemental vitamin D daily, starting in the first few days of life. In practice, this is usually given as vitamin D drops, a small daily dose placed in your baby’s mouth or on your nipple before nursing. Despite this recommendation, most infants are not receiving it. The AAP published a study finding that only 27.1% of infants met the vitamin D intake guidelines.

An alternative approach to supplementing vitamin D for your baby is to increase your own intake, which raises the amount that passes through your breastmilk. A randomized controlled trial of 334 breastfeeding mother-infant pairs tested this theory. It compared mothers taking 6,400 IU per day with no drops for the baby against the standard approach of 400 IU per day for the baby. The babies whose mothers took 6,400 IU reached the same vitamin D levels as the babies who received their own drops. The researchers concluded that maternal supplementation at 6,400 IU per day safely supplies breastmilk with enough vitamin D to meet a nursing infant’s needs, offering a real alternative to infant drops.

An earlier, smaller study reported similar findings and concluded that a maternal intake of 4,000 IU per day could substantially improve maternal and infant vitamin D status. The takeaway here is that if you are breastfeeding and you increase your vitamin D with a supplement, that will increase the vitamin D delivered to your baby through breastmilk. If you have any questions about whether your baby is getting enough, this is a great conversation to have with your pediatrician.

Weighing the Risks and Benefits

Let’s tie all of this together with some practical takeaways. The big picture is that vitamin D is essential for your health and your baby’s. Plus, deficiency is common, and most people, including many pregnant moms, are not getting enough vitamin D.

The best way to know your levels is a blood test. However, routine testing is not always recommended or covered by insurance. If you test, you can know exactly how much you should supplement with. You may be a stronger candidate for a test if you have darker skin, get very little sun, cover most of your skin for religious or personal reasons, are obese, have a condition that affects fat absorption, or were deficient in a past pregnancy. In those cases, knowing your starting number can help you and your provider decide how much to supplement, rather than guessing.

The next step is to estimate how much vitamin D you are realistically getting. Look at your sun exposure, factor in how much time you spend outdoors, where you live relative to the equator, the season, your sunscreen use, how much skin is exposed, and your skin tone. Next, you want to check how much vitamin D your prenatal vitamin contains. It is likely around 400 IU but may be more in higher-quality brands. Then you should consider how often your diet includes vitamin D-rich foods.

You also have the option to skip the test and simply supplement. This is where the current guidance leans. While the guidance can feel confusing, the evidence consistently supports intakes above the 600 IU RDA during pregnancy. Several studies, along with the latest Endocrine Society guidance, support daily amounts in the range of 1,000 to 4,000 IU.

Vitamin D is inexpensive and takes almost no effort to add to your routine. Remember that toxicity comes from taking very high amounts over an extended period, not from an occasional higher dose, and it generally requires sustained intakes well above what anyone takes in pregnancy. None of the research reviewed for this episode found adverse effects from supplementing below the toxicity threshold. The downside is minimal as long as you are not overdoing it. The upside is ensuring you and your baby get enough vitamin D to support everything from healthy bones to immune function.

Talking to Your Doctor, Midwife, or Pediatrician

As always, talk to your doctor, midwife, or pediatrician before starting any supplement. If you are concerned about your D levels, you can advocate for a test, especially if you fall into a higher-risk group. Keep in mind that depending on your provider and insurance, testing may be an out-of-pocket cost. If you have any questions, your care provider is the right person to help you sort through them for your specific situation.

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