How Well Do You Convert Beta-Carotene to Vitamin A?

Everyone knows that carrots and sweet potatoes are great sources of vitamin A, right?

Well…  it turns out it isn’t that straightforward for everyone. The beta-carotene in orange fruits and vegetables has to be converted into the form of vitamin A (retinol) that our bodies can use.

Genetics plays a huge role in how well you convert the carotenes into retinol. Some people are great at absorbing and converting the carrots in their diet into the retinol form. Others of us carry genetic variants that significantly impair that conversion.

Background information on Vitamin A:
Vitamin A is a general term that covers several different forms of the vitamin.

Animal food sources mainly provide retinyl palmitate, which is broken down in the intestines to retinol. In this form, it is stored by the body and then converted to an active form for use.

Carotenes are the plant forms of a precursor to vitamin A. The most common form is beta-carotene which is found in abundance in carrots and other orange-colored foods. Beta-carotene is broken down by an enzyme in the intestines to also form retinol.[source]

Interestingly, most carnivores are poor converters of beta-carotene, and cats cannot create any vitamin A from beta-carotene.

About 80-90% of the retinoids in the body are stored in the liver and used to maintain a steady level in the blood.[ref]

Your body then used the retinoids in a variety of ways including in:

  • stem cells,
  • photoreceptors in the eye,
  • epithelial cells,
  • embryonic cells,
  • various immune cells,
  • red blood cells

A deficiency in vitamin A can cause poor night vision, worsen infectious diseases, and, when severe, cause blindness.  In the immune system, retinol is involved with both the innate and adaptive immune responses.[study] Vitamin A can also help with skin problems such as some types of acne and hyperkeratosis.[study]

Personal side-note:
I had keratosis pilaris (bumpy skin on the back of my arms) since childhood and never knew what caused it. After learning that I don’t convert beta-carotene very well, I starting taking a retinyl palmitate supplement. A couple of months later, my arms were smooth for the first time in several decades. (To be totally honest here, I didn’t realize the connection until I stopped taking the vitamin A supplement and the bumps came back a month later. I now judge my vitamin A status by the smoothness of my arms. )


Genetics of Beta-carotene Conversion:
Beta-carotene is converted by the enzyme β-carotene 15,15′-monooxygenase (BCMO1 gene) into retinol. It is then used by the body in the same way as preformed vitamin A from animal products is used or stored.

There are two gene variations in the BCMO1 gene that help determine a person’s ability to convert beta-carotene into the retinol a body uses. A study in 2008 shows that the SNP’s rs12934922 and rs7501331 control a person’s conversion rate of beta-carotene into retinol.

People with a T allele on both rs12934922 and rs7501331 have a 69% decreased conversion of beta-carotene to retinol.  For people with only a single T in the rs7501331 SNP, the conversion is decreased by 32%.

Check your genetic data for rs7501331 (23andMe v.4 and v.5, AncestryDNA):

  • C/C: normal
  • C/T: decreased beta-carotene conversion
  • T/T: decreased beta-carotene conversion

Check your genetic data for rs12934922 (23andMe v.4 and v.5):

  • A/A: normal
  • A/T: decreased beta-carotene conversion
  • T/T: decreased beta-carotene conversion

Three other variants that are found near the BCMO1 gene have also been shown in a small study to affect the rate of conversion by about 50%

Check your genetic data for rs11645428 (23andMe v4, v5, AncestryDNA):

  • G/G: lower (normal?) beta-carotene conversion
  • A/G: higher beta-carotene conversion
  • A/A: higher beta-carotene conversion[ref]

Check your genetic data for rs6420424 (23andMe v4, v5, AncestryDNA):

  • A/A:  lower beta-carotene conversion[ref]
  • A/G: slightly lower beta-carotene conversion
  • G/G: normal beta-carotene conversion

Check your genetic data for rs6564851 (23andMe v4, v5, AncestryDNA):

  • G/G: lower beta-carotene conversion (thus higher circulating beta-carotene)[ref]
  • G/T: somewhat lower beta-carotene conversion
  • T/T: normal conversion

Lifehacks

Vegan and Vegetarian Diets:
If you eat a vegan or vegetarian diet, your body’s source of vitamin A is through converting beta-carotene. If you don’t process it into retinol very well, you may want to increase your vegetables that are high in beta-carotene or consider supplementing with a retinol form Vitamin A.

Beta-carotene is hydrophobic and needs fat to be absorbed in the intestines. Adding a little fat to your beta-carotene rich food should help a little with absorption.[ref]

A word of caution:
Vitamin A is a fat-soluble vitamin that can build up in the body, so you don’t want to go overboard with it. You can get a blood test to determine your level.

The upper daily recommended limit of vitamin A is 3000 μg/day (3 mg/day). Most supplements list the amount of vitamin A in IU (international units). One IU is equivalent to 0.3 μg (.0003 mg) for vitamin A. So 8000 IU would equal 2.4 mg retinol.

So how much beta-carotene is in carrot juice?
According to the Nutridesk website, one cup of carrot juice contains 22mg of beta-carotene. That site also claims that for an average person, 1/12th of that beta-carotene is converted into retinol thus giving 1.8 mg of retinol per cup of carrot juice. If you are a poor converter of beta-carotene, you could be getting more like 0.5mg from a cup of pure carrot juice.

Retinol forms of vitamin A:
Carlson’s Vitamin A on Amazon.com is an inexpensive source of the retinol form of vitamin A. There are other good brands as well — just be sure to read the labels to know what you are getting.

Beef liver is also an excellent source of vitamin A. A three-ounce serving of liver packs a big punch with about 15,000 IU of vitamin A.

Include Vitamin D:
There are a few studies that show that too much vitamin A without enough vitamin D can be a risk factor for osteoporosis.[ref]  So be sure to get out in the sunshine for vitamin D, and if you are getting your vitamin A levels checked, you may want to also get vitamin D tested at the same time.

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21 Comments on “How Well Do You Convert Beta-Carotene to Vitamin A?

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  2. Can a person be overly efficient at converting carotenes to retinol and so risk vitamin A sub-toxicity by eating a diet very high in carotenes?

    • Good question :-) I don’t know of any genetic variants that cause extremely high rates of conversion. According to the Linus Pauling Institute at Univ. of Oregon, there is no worry of toxicity from eating sources of beta-carotene: http://lpi.oregonstate.edu/mic/vitamins/vitamin-A#toxicity I think the worst you will have from a diet that is very high in carotenes is turning orange – called hypercarotenosis.

  3. Question: I have a TT and a CT on the above, so I have a decreased beta-carotine conversion. My question though is about topical retinol/retin-A. Do these genetic markers affect the way the body absorbs vitamin-a topically? I am asking because the several times I was prescribed tretinoin or retin-a micro, I had an adverse reaction. I stuck through the so called purging and dry/red/flaky period of about 4-6 months but my skin only continued to get worse until I had to stop. The doctor had no explanation for me and basically said everyone takes well to these topicals. I guess I’m an anomaly. Just wondering if these alleles have something to do with this.

    • Hi Amber,
      I don’t think that the decreased beta-carotene conversion would affect topical retin-A. My guess would be that you are somewhat allergic to something in the topical creme?
      I’ve read that you can open up the liquid vitamin A gel caps and put them directly on your skin. That may be a way to see if it is the vitamin A that is irritating your skin vs something else in the cream. You might want to try it on a weekend though –the vitamin A gel cap that I tried on my skin smelled a bit like fish and the odor lingered…
      Have you tried taking a true vitamin A internally? Personally, I had keratosis pilaris (little bumps) on the back of my arms and on my thighs since childhood and didn’t know what caused it. When I found out that I didn’t convert beta-carotene very well, I started taking vitamin A. After a month or so, I noticed that my arms were smooth, but I didn’t really make the connection to the vitamin A until I stopped taking it and the bumps came back. That was a few years ago, and I now kind of use the smoothness of my arms as a way to know if I’m getting enough vitamin A. Like the rest of the fat-soluble vitamins, I don’t want to go overboard on vitamin A.
      Good luck on getting it figured out!

      • Too much or too little thyroid also interfere with the conversion of carotene into vitamin A. Many of the people with autism have keritosis pilaris. Discussion groups claim it is due to too much carotene compared to vitamin A. (Carotene can interfere with the receptors for vitamin A.) In my daughter’s case, added thyroid got rid of most of her keritosis pilaris.

        • Hi Polly,
          Thanks for reading and adding to the discussion on beta carotene / vitamin A.
          Yes, vitamin A levels are important in thyroid hormone – and vice versa. It is interesting that added thyroid got rid of your daughter’s keratosis pilaris. I had the opposite – thyroid didn’t help my keratosis pilaris, but taking vitamin A cleared it up. I now judge whether I need more vitamin A based on how the backs of my arms look :-)
          Debbie

    • Hi Amber,
      I also have CT on my BCM01. Are you supplementing Vitamin A? I’m having trouble understanding A. If I need to B. If I have the correct kind. I purchased Vitamin A Retinyl Palmitate 2400 mcg and was hoping to see if anyone knows if that is the correct from/dosage.

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  5. are there other genes that make humans and cats need certain forms of vitamins due to poor conversion besides these and MTHFR? I’m asking because I noticed signifigant differences when when taking vitamin A instead of beta carotene supplement and an activated b-complex with methylfolate and methylcobalamin instead of basic folic acid and cyanocobalamin.

    • Hi Shallah,
      Not sure about cat genes… :-)
      But yes, there are lots of genetic variants that affect our need for vitamins. Check out my articles on MTHFR, vitamin D, vitamin K, vitamin C, iron, and more. There is a whole category of articles on vitamins and minerals.
      Debbie

  6. I believe I am not converting beta carotene because my hands get orange when I eat too many carrots and butternut squash. I don’t have jaundice. Is there anything I can take, supplement wise, to help my liver convert. I am going through a major heavy metal detox and my liver is definitely overburdened due to the fact that I can’t tolerate a lot of liver supplements.

    • Hi Teresa,
      Thanks for commenting on the Beta-carotene article. From what I’ve read on the topic, turning orange from too much carrot juice, etc is due to your body not breaking down the beta-carotene and storing it instead. I haven’t seen anything to indicate that it is harmful…
      I’m honestly not sure if there are any specific liver supplements that would help you convert more beta-carotene. Did you check your genes to see how well you should be converting beta-carotene?
      Debbie

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  8. Hi there. I am heterozygous CT on BCM01. Do I need to supplement with Vitamin A and if so, what is the best way to do that. I purchased a supplement that is Vitamin A as Retinyl Palmitate, 2,400 mcg. Is the correct form/dosage?

    • Hi Teresa,
      As far as whether you need to supplement with Vitamin A… that would depend a lot on your diet. If you are eating liver or other high vitamin A foods, you may not need any more vitamin A. One way to know for sure if you need to supplement with vitamin A would be to get a blood test done.
      Retinyl Palmitate is the active form of vitamin A that should work well for someone who doesn’t convert beta-carotene very well. You might want to talk to your doctor or get a blood test done if you are uncertain about dosages.
      Debbie

      • As far as I’ve read, serum retinol levels aren’t good indicators of overall body levels of vitamin A. It seems similar to magnesium. The liver can be quite saturated and yet blood tests don’t correlate. I’m no expert, but please consider this possibility. There are many variables including ones ability to manufacture retinol binding protein. I’ve read retinyl esters in the blood can provide better feedback, possibly. Vitamin A has been implicated in osteoporosis with or without vitamin D. So be careful.

        “Assessing vitamin A status in persons with subtoxicity or toxicity is complicated because serum retinol concentrations are nonsensitive indicators in this range of liver vitamin A reserves.” – Acute and chronic toxic effects of vitamin A, The American Journal of Clinical Nutrition.

  9. Please include more information about taking too much vitamin A and Retinols during pregnancy as it is linked to birth defects.
    I just found out that I have built up chemical toxins that my liver hasn’t been getting rid of which is leading me to research genetic reasons for this. After looking at my 23 & me raw data, I notice I have a number of genetic predispositions with converting beta carotene. However, I know that when I choose to try to conceive, using too high dose of synthetic vitamin A can be harmful. So please proceed with caution if trying to conceive. This worries me because I want to make sure I’m getting enough.

    • Hi Rachael,
      Thanks for posting this reminder to everyone not to take high dose synthetic vitamin A while trying to conceive (without a doctor’s recommendation).
      Vitamin A is vital for a healthy pregnancy — but you definitely don’t want to go overboard on it.
      Here is an (older) journal article that breaks down some of the recommendations on amounts and includes information on eating liver: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1664333/?page=1
      This article from the American Journal of Clinical Nutrition (written in 2000) is also good: https://academic.oup.com/ajcn/article/71/5/1325S/4729494 It does say that 20 cases of birth defects had been recorded due to excess vitamin A over the past 30 years.
      Debbie

  10. Thank you so much for posting this info! I had my DNA tested by 23andme and didn’t know about these results, clicked on the links you provided and found I have 4 markers for decreased or low normal conversion. It fits with my other results, being over 80% NW European descent and the diet they ate…not many plants. Thank you again.

    • Thanks for reading and commenting. For me, it is always interesting to see how my genes match up with what would have been a normal diet for my ancestors over the past 500 years or so – organ meats for the vitamin A and B12; fish for the DHA/EPA; high amylase to break down oats and potatoes.
      Debbie

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