Liz talks about why a nutrient that is so important for fetal development can also be so dangerous for fetal development (that’s *mild* sarcasm). No surprise: we need some context, nuance, and real talk about vitamin A, especially when it comes to pregnancy. Check out Baby Making and Beyond for more baby making Q&A!
This is episode 21, topic: Liz talks vitamin A – and eating liver – in pregnancy. What does the science say?
In case you missed it, in episode 20 I talked to Dr. Kelly Blodgett of Blodgett Dental Care – we talked about holistic dentistry, root canal removal, and implant/replacement options after an extraction.
Before I begin, I want to quickly thank Arrowhead Mills for their generous sponsorship of this podcast. next time you go to the store, I’d love to have you support a company that supports MY work, and look for Arrowhead mills products. You can also find them on Vitacost.com! Arrowhead Mills pancake mixes are ALL we use for our saturday morning pancake tradition, because I tried ALL the options – including homemade pancake mix – and none of them were as consistently good or as easy as arrowhead mills.
This week’s podcast comes from a question I recently got via DMs about whether liver is dangerous in pregnancy (and when we ask about liver in pregnancy, we’re actually asking about vitamin A, which is the nutrient in liver that’s thought to cause birth defects). It’s funny, because I’ve been doing the “real food thing” for so long, I sort of forget to recycle the information that I’ve produced in the past. I am always looking for the next NEW topic, when in reality there are things that are worth updating and bringing up cyclically to ensure everyone has gotten a shot at the information.
I’ve talked about liver and vitamin A in pregnancy in a few different places over the last decade, inspired and informed by a few different corners of the food world. Ten years ago, it was the Weston A. Price foundation that was really singing the praises of both liver as a source of vitamin A, and naturally-occurring vitamin A itself for pregnancy. I think that’s really where the Paleo community discovered the information, and then ran with it. The idea that liver is a superfood. You can see my post from 2014 at realfoodliz.com called “the raw liver smoothie shot.” Not something I still do, but something I did and, ya know, No Ragrets. Around that time I also found the work of Ray Peat and of course, Danny Roddy and started learning about what those great minds think about liver, its role in supporting the thyroid, and now, why desiccated liver supplements might NOT be a great option. That’s probably for another show, but today I’d like to bring this topic back up, talk about what I know and the mountains of investigative work our lead researcher, Amanda Torres, did on the topic for the Baby Making and Beyond program.
So yes, this information is a peek into the Baby Making and Beyond program that I released when my first was just a few years old! We worked SO hard to fact check literally every single thing we said in that program, and I’m still so proud of it. While I may have said these same things elsewhere, I thought it was time to cycle them back in. So what’s to follow is a DEEP DIVE into all the context and nuance around the vitamin A in pregnancy question, based on the hard work of our research lead on the project. Please note, however, that while we are confident we nailed this one, this is an interpretation of the evidence. Some will find it inadequate, some will find it overly detailed. Some will find our conclusions conservative and others will think we’ve gone off the deep end. This is information, and as always, it’s important that you do what you’re comfortable with, and
that you consult with a professional that knows YOU.
Why It’s Important: Vitamin A in fertility, pregnancy, & postpartum
Vitamin A in Fertility
Vitamin A is involved in thyroid function (both male and female), which promotes healthy production of hormones critical to fertility, and it’s important for male testosterone levels and sperm formation. (Source 1, 2, 3, 4).
Animal studies suggest that vitamin A might even play a role in implantation – the critical step between fertilization and pregnancy.
(Remember, often, in reproductive science, animals are tested due to the ethical concerns of human testing.)
Vitamin A in Pregnancy
Vitamin A is involved in the health of the placenta and the embryo, and helps determine the formation of the spinal cord, eyes, heart, kidney, limbs, and lungs (source). It is important all the way through the 3rd trimester, when baby builds up their own vitamin A stores. Babies born prematurely show inadequate vitamin A levels (source), which puts them at risk for respiratory, eye, and GI-related issues.
Interestingly, the placenta likely plays a role in protecting the fetus from vitamin A toxicity, to a degree (source). This doesn’t mean vitamin A can’t cause birth defects, however – planning your intake is still important.
Vitamin A in Postpartum
Vitamin A supports tissue health and a robust immune system after birth (source). Baby’s vitamin A stores continue to build with the vitamin A content of breastmilk, beginning with colostrum, which is rich in vitamin A (source).
Formula contains supplemental vitamin A, although we don’t know how the vitamin A in formula might work compared to the vitamin A in breastmilk.
Breastfeeding moms need consistent, adequate vitamin A in their diet to pass it along via breastmilk in sufficient quantities for baby’s long-term health (source). According to this study: “…even the milk of a mildly undernourished woman may meet the physiologic needs of the newborn during the first weeks. After this time, however, a rapidly-growing infant may exhibit negative vitamin A balance, with severe consequences for health…” which may include an increased risk of contracting diarrhea, respiratory infections, and infectious disease.
Even if mom isn’t able to breastfeed, vitamin A will still boost her health and support tissue repair during the transition into parenthood. Inadequate vitamin A status makes people more prone to infections – and no parent has time for that! (Source).
This all means that mom’s diet should contain the proper amounts – not too much, not too little – of vitamin A all the way up to delivery and beyond.
What You Need to Know
There are a few important facts you need, but the number one most important thing you need to know is this:
THERE ARE SEVERAL FORMS OF VITAMIN A, AND THEY ARE NOT THE SAME.
To understand this fully, let’s quickly go over the terminology.
The two important forms of vitamin A found in food are retinol and beta carotene. The forms of vitamin A found in supplements are usually retinyl palmitate or retinyl acetate (forms of retinol) and/or beta carotene. Both retinol and beta carotene are often listed as “vitamin A” on nutrition and supplement labels. This can be confusing!
Also confusing: you might see a few different terms used for measuring the vitamin A content of foods and supplements. Micrograms (mcg or μg), International Units (IU), and Retinol Activity Equivalents (RAE) are all common. This becomes most important when quantifying retinol, and we prefer to use the mcg measure because it’s the most exact measurement possible. (We’ll translate it to IU when appropriate.)
Retinol (also called “preformed vitamin A”) is the form of vitamin A that directly supports fertility, proper fetal development, and overall health.
Retinol is only found in animal products, including eggs, butter, milk, liver, and cod liver oil.
Any beta carotene we consume must be converted to retinol before it can play most crucial roles in fertility, pregnancy and postpartum – this is why most scientific research on vitamin A (for example, the studies referenced previously) are not talking about beta carotene.
As important as it is, retinol must also be treated with caution – too much can cause birth defects. This is why our recommended retinol intake is less than ⅓ of the lowest toxicity threshold ever suggested in the scientific literature; and why we recommend augmenting dietary intake of retinol with beta-carotene-rich foods.
Beta carotene is a precursor to retinol. You might also hear it referred to as “provitamin A.”
It’s found in leafy greens and brightly-colored plants like orange and yellow vegetables, and is known as a carotenoid. There are other carotenoids in the foods we eat, but beta carotene is the most studied and best understood.
When the body has sufficient levels of retinol, whether from beta carotene conversion or retinol-rich foods, it won’t continue converting beta carotene to retinol. (This is called a “negative feedback loop.”)
Beta carotene is beneficial to the body (it may even play a protective role for the corpus luteum), but it can’t directly do what retinol does.
So: retinol and beta carotene are related, but extremely different!
(…There’s a parent-child joke in there somewhere.)
THE CONVERSION OF BETA CAROTENE TO RETINOL
“Precursor” means that, under the right circumstances, the body can convert beta carotene into retinol.
Under the right circumstances.
Unfortunately, there’s a myth floating around that the body is able to get all the vitamin A (retinol) it needs from beta carotene.
This is simply not accurate. It’s well-known among scientists that the body’s ability to convert beta carotene to retinol is imperfect – and sometimes unpredictable.
Not only is the known conversion rate from beta carotene to retinol 2:1 at best using purified beta carotene – and some estimates state as low as 12:1 or 24:1 for beta carotene from other sources, including food – but there are also multiple other, less predictable factors that can impact a person’s ability to convert beta carotene.
Scientists refer to these other factors with the acronym “SLAMENGHI” (source 1, 2). Each letter represents one factor that can impact beta carotene conversion, ranging from the type of food, nutrient status, genetic factors, age, gender, and more.
More on SLAMENGHI (you don’t need to know this, but just for funsies):
S: Species of carotenoids. This refers to the relative bioavailability of varying carotenoids, like beta carotene.
L: Molecular linkage. This refers to other compounds chemically linked to carotenoids.
A: Amount of carotenoids consumed.
M: Matrix in which the carotenoid is incorporated. This refers to HOW the carotenoids consumed are housed (think: in food of varying types)
E: Effectors of absorption. How other nutrients and/or drugs change how it’s absorbed.
N: Nutrient status of the host. The retinol status of the “host” (that’s you and me) actually makes beta carotene better absorbed and converted. Zinc and iron status is also important (source).
G: Genetic factors. There are dozens of genes that have been studied for their impact on beta carotene utilization, but the most common genetic SNPs (or polymorphisms) discussed are BCO1 and BCMO1. I (Liz) have several of these – and I didn’t know this when I was pregnant.
H: Host-related factors. This is everything from age to gender to individual pathologies.
I: mathematical Interactions. This refers to the sum of the effect multiple SLAMENGHI factors have vs. one in isolation.
It makes sense, then, that this study states that “a safe vitamin A intake in general cannot be reached by consuming only one component ([retinol] or [beta]-carotene) alone…” In other words, we need both beta carotene and retinol from the diet to reach proper levels of vitamin A intake.
If all this is true, why are so many people advised, especially in pregnancy, to get all their vitamin A from beta carotene?
There are a few possible reasons.
Reason #1: There’s the long-held myth that retinol-rich animal foods are unhealthy and plant foods aren’t (we can’t possibly get our vitamins from something like egg yolks! Better eat more carrots instead).
Reason #2: There’s the fact that most of us weren’t raised on some of the more vitamin A-rich foods, like liver, so they seem scary. (Our grandmothers probably wouldn’t have batted an eye.)
Reason #3: Perhaps most importantly, many of us have been told that vitamin A as retinol – the most commonly named food sources in this debate are liver and cod liver oil – causes birth defects.
Let’s talk about #3.
VITAMIN A TOXICITY & BIRTH DEFECTS
When pregnant moms are advised to “avoid vitamin A” from supplements or foods like liver or cod liver oil, it is due to the potential for retinol to cause birth defects at elevated levels of intake.
The concerns about retinol intake in pregnancy are real. High levels of vitamin A as retinol can absolutely cause birth defects and pregnancy loss.
What are considered “high levels?” While different studies have suggested varying toxicity levels for retinol, the most commonly-referenced study calculated this effect as occurring at intakes above 3,000 mcg/day (10,000 IU).
This is also the lowest level of vitamin A intake ever associated with toxicity in the scientific literature. No toxicity has ever been observed at lower levels of intake.
Still, this is a controversial finding, with many scientists claiming that much higher levels are safe and even necessary; nevertheless, it was the finding that was adopted into most mainstream recommendations (source).
Despite this controversy, a too much is bad, so none is best approach has taken root as a result – which really throws the baby out with the bathwater, since too little vitamin A can also cause birth defects and improper development of major organs (source).
Even so, we don’t want to swing the pendulum too far in the opposite direction. Yes, vitamin A is important, but more is not necessarily better. The science reflects this, and historical context does, too: until recently, most foods rich in retinol were quite rare; a small amount of cod liver oil takes an extreme amount of effort to produce, and liver is only a small part of the animals we eat. These foods are simply not appropriate for daily use.
Even the recent pioneers of these foods, like Dr. Weston Price, recommended only small amounts, often to correct deficiencies of vitamins (like vitamin A) that are stored in the body.
To reiterate: as a fat-soluble nutrient, vitamin A is stored in our bodies, so a little bit goes a long way.
Other Risks & What We Don’t Know
There are several things we don’t fully understand about vitamin A intake, and we want to be very direct with you about them.
We know that vitamin A as retinol is a fat-soluble nutrient, so it’s stored in the body.
Knowing that retinol-rich foods like liver and cod liver oil and retinol-containing supplements were not abundantly available until recent decades, there is a possibility that a dietary abundance of liver, cod liver oil, or other vitamin A supplements for an extended period of time could supply too much.
This means that if you’ve previously eaten a retinol-rich diet (for example, if you’ve ever eaten liver weekly or cod liver oil daily for a long period of time), or if you’ve consumed high amounts of vitamin A-fortified food (in the United States, low-fat milk is fortified with vitamin A) you might have adequate vitamin A stores already.
We don’t know how long each individual will store vitamin A, and we don’t know how different factors (see SLAMENGHI, above) will impact your vitamin A levels.
Interestingly, one study showed that eating liver raises certain teratogenic (teratogenic means birth-defect-causing) vitamin A metabolites in the body more than the equivalent amount from supplements (source); however, vitamin A intake was much higher in this study than we recommend, so we don’t yet know what this may mean and will keep an eye on the literature for further insight. (Liver is incredibly nutrient-dense and contains folate, choline, vitamin B12, and iron, so, for most people, we’d still support incorporating moderate amounts in your diet.)
If you suspect you’ve eaten too much retinol-rich food, too frequently, for too long (this is rare, but some liver, cod liver oil, or supplementation aficionados might be at risk); or if you have any signs of vitamin A excess, including hair loss, blurred vision, or flaking skin, talk to your practitioner and consider testing before getting pregnant. You can test your vitamin A levels with a serum vitamin A test, which can be ordered directly in most states, without a doctor, from Request A Test.
Because striking a balance with vitamin A is so important, this simple test can be useful – and having the information can relieve some stress. Be sure to have your practitioner help you interpret your results.
Where to Get It & Our Recommendations
We recommend somewhere around 770 mcg retinol (~2,500 IU) per day during pregnancy.
This is also significantly lower than the 3,000 mcg (10,000 IU) toxicity threshold. No increase in defects has ever been observed at intakes lower than this (source).
Where we differ slightly from mainstream recommendations is in our suggestion to hit the RDA target with retinol instead of relying solely on beta carotene, and to add plenty of beta carotene rich foods after that.
We make this recommendation based on what we know about vitamin A toxicity, beta carotene conversion, SLAMENGHI factors, and the negative feedback loop that will limit excess conversion of beta carotene.
Of course, beta carotene is useful in for its own reasons – it’s an antioxidant, and animal studies suggest it promotes progesterone synthesis in the corpus luteum (source 1, 2).
Keep in mind that the benefits of beta carotene-rich foods go well beyond vitamin A! They’ve got fiber, polyphenols, magnesium, and other awesome nutrients, too.
Retinol Content of Common Foods & Supplements
Note that these are approximations; retinol content will vary based on the animals’ diets. You can include the following as PART of your vitamin a intake, but we don’t recommend using them alone, or even daily.
- 3 capsules of Rosita Extra Virgin Cod Liver Oil has approximately 210 – 287 mcg retinol (source). Nordic Naturals Cod Liver Oil contains much less. Note that we recommend taking cod liver oil only 2-3 times per week, if you choose to take it at all.
- 1 oz chicken liver has approximately 1,121 mcg retinol. ⅔ oz would supply approximately 672 mcg retinol. Note that 3 of our Bacon Beef Liver Bombs would contain 1 ounce of chicken liver if made as directed.
- 1 oz beef liver has approximately 2,700 mcg retinol (be mindful of intake, this is extremely rich in retinol)
- ~1oz USWM liverwurst has approximately 568 mcg retinol
- ~1oz USWM braunschweiger has approximately 1,387 mcg retinol (be mindful of intake, this is extremely rich in retinol)
- 3 Vital Proteins Beef Liver Capsules have approximately 768 mcg retinol
- 1 large pastured egg has approximately 74 mcg retinol
- 4 oz full-fat grass fed milk has approximately 56 mcg retinol
- 1 tablespoon of butter has approximately 14 mcg retinol
Keep in mind that the nutrient content of real food can vary, but as long as your serving size is consistent, it’s extremely unlikely that it would vary enough to push you from a safe 770 mcg (2,500 IU) to over 3,000 mcg in a given day.
We recommend you vary your intake of the most retinol-rich foods.
Tracking Your Intake
Know your “hidden sources” of vitamin A. In the United States, low-fat milk is fortified with retinyl palmitate. While we don’t recommend low-fat anything, be aware if you include it in your diet.
Check your prenatal. While most prenatals do not contain retinol, some do, including a few we like. This can be useful in hitting your vitamin A target, but be mindful to include any retinol from prenatal supplements in your calculations.
Eat the other important nutrients, too. The body requires nutrients like vitamin D, vitamin K2, zinc and iron to use vitamin A properly. This is pretty simple when you focus on real food: egg yolks and cod liver oil contain both vitamins A and D; salmon and sardines (and sunshine!) are also sources of vitamin D. Oysters contain zinc and liver contains iron. Several of our recommended prenatals contain vitamin K2, and it’s also present in small amounts in ghee and – for the adventurous – emu oil.
Vitamin E protects against vitamin A toxicity – avocados, nuts and seeds, and cod liver oil are sources of vitamin E (source).
Watch your genetic factors. If you know you have factors that impact your ability to convert beta carotene to vitamin A in the first place (like the genetic SNPs BCO1 and BCMO1) and you’ve tested low for serum retinol, be extra mindful to hit your targets with vitamin A from retinol.
Just because you’ve got a SNP doesn’t mean it will affect you negatively; however, if you have one or more, it increases your likelihood of experiencing conversion issues.
You can determine your genetic factors by uploading your 23 and Me results to an analyzer like Promethease (more user-friendly) or Livewello.
Can I skip the Vitamin A rich food (bleh) and just rely on supplements?
Wellllll yes, you could; however, no supplement can perfectly replicate the synergy of nutrients from real food.
If you choose to skip the extra-rich sources of retinol (and, we get it – liver pills, cod liver oil, and braunschweiger aren’t everybody’s bag) at the very least, get plenty of egg yolks. These are incredibly valuable for their choline content.
Also be sure to watch your intake of other nutrients, like those mentioned above: vitamin D, vitamin K2, zinc and iron.
What’s the deal with IU vs. micrograms?
The bad news is: vitamin A terms, supplement (prenatal) labeling laws, and conversion factors are a rabbit hole of confusing terminology and calculations. There’s International Units (IU), a term that’s being phased out on supplements as of 2018/19, and Retinol Activity Equivalents, a term meant to define how many micrograms of carotenoid is required to equate to the biological activity of one microgram of retinol. Because retinol is retinol, we use the mcg measure and recommend getting your RDA of vitamin A as retinol.
Before getting irritated about this confusing labeling, know that while we certainly wish the labels were more precise, we don’t think it’s all necessarily bad. Retinol is critical, but it’s one we need to deal with thoughtfully.
The good news is: You REALLY don’t need to understand any of that.
Just remember that beta carotene and retinol are different, and that we need both beta carotene from plants and retinol from animal products for safe intake levels of vitamin A.
Remember that what our bodies need to play the important roles we discussed is retinol, and that it’s a safe bet to hit your minimum vitamin A requirement in pregnancy (770 micrograms) using retinol.
What other cool stuff can retinol do?
It may protect against anemia, likely because vitamin A helps the body use its iron stores. This might be one reason why liver, which is dense in vitamin A and iron, could be so powerful (in the proper amounts). In one study, vitamin A supplementation alone reversed anemia without supplemental iron in 35% of women. When paired with iron, anemia was reversed in 97% of women (source).
Should I get more than the recommended 770 mcg (2,500 IU) vitamin A from retinol? I’ve read that up to 6,000 mcg (20,000 IU) are safe.
Some non-BMB sources recommend significantly higher daily intake of retinol from animal sources like cod liver oil – up to 6,000 mcg (20,000 IU) per day. We believe these higher recommendations are made based on improper analysis of available data and information.
That’s why we advise you not go higher than our recommended levels during pregnancy without the clearance of your practitioner.
Vitamin A is a “controversial nutrient” during pregnancy – so it’s no surprise that we tackle it in Baby Making and Beyond!
There are two main types of vitamin A; beta carotene and retinol. While beta carotene is considered safe in pregnancy, retinol is often said to be unsafe. We’ll discuss why, and whether this recommendation stands up to scrutiny. .
Spoiler alert – here’s what we conclude based on the evidence:
- Science suggests that 770 mcg (2,500 IU) vitamin A from retinol each day is safe and poses no risk of toxicity in pregnancy.
- It’s important to monitor your retinol intake: while there are many reasons to emphasize vitamin A as retinol in the diet, it’s a “goldilocks nutrient” – too little can be dangerous, but too much can be, too.
- If you aren’t getting the right amount of retinol from dietary sources (which is common), choose a prenatal with appropriate levels. Always be sure to factor your retinol-rich prenatal into your daily retinol intake.
- Be aware of the factors that impact individual vitamin A status: genetics, lifestyle, and current and past food choices. Because vitamin A as retinol is a fat-soluble vitamin, it is stored in the body; this means that vitamin A stores (and thus, vitamin A needs) can vary from person to person.
- Both types of vitamin A are important: retinol from animal sources and beta carotene from plant sources.
And that’s it! That’s the vitamin A story as seen through the lens of our team. I hope you enjoyed it, and I hope you found some nugget of info that’s useful to you, or at least something to fact-check for your own comfort and knowledge!
No overshare this week!a big thank you to Arrowhead Mills for making this episode possible – I hope you enjoyed it! Don’t forget to follow @realfoodliz on Instagram, or if you’ve made the VERY wise decision to NOT be on social media, catch me on my email list! You can go to realfoodliz.com to get on the list. I appreciate you! I’ll see you next week.