BCO1: Why Some People Get Less Vitamin A From Vegetables
The gene that decides how much vitamin A you actually get from carrots.
Your DNA does not change what beta-carotene is. It changes how much vitamin A you actually get out of it. BCO1 makes the enzyme that converts beta-carotene from carrots, spinach, and supplements into the retinal your body can use, and two common variants slow that enzyme down. Roughly four in ten people are slow converters and most have no idea. If that's you, plant sources give you less vitamin A than the numbers imply, and preformed retinol is the easier path.
What BCO1 does
BCO1 is the gene that lets your body turn beta-carotene from plants into actual vitamin A. The orange in carrots and sweet potatoes is beta-carotene, a provitamin. It does nothing for you until an enzyme called beta-carotene 15,15'-monooxygenase snips it into retinal, the form your body uses. BCO1 codes for that enzyme. People with the common slow versions get less vitamin A out of the same plate of vegetables, sometimes a lot less.
This is one of the better-studied nutrition genes, and it explains something researchers noticed for years before they had the genetics to back it up: give two healthy people the same dose of beta-carotene and one ends up with several times more vitamin A than the other. Up to about 40 percent of people are poor converters. Two coding changes in BCO1 account for a good chunk of that spread.
The practical read is simple. If you carry the slow variants and you lean on plant foods or beta-carotene supplements for your vitamin A, you may be getting less than the label suggests. Preformed vitamin A, the retinol kind found in liver, eggs, dairy, and fish, skips the conversion step entirely, so your genotype does not slow it down.
Your variants, decoded
rs7501331 is the workhorse variant here, the one with the cleanest human data. It changes amino acid 379 from alanine to valine, which is why you'll see it written as A379V. The T allele is the slow one. Heads up on letters: this comes from dbSNP, and a 23andMe or AncestryDNA export reads whichever strand the chip uses, so yours may print the complementary letters instead (a C shows as G, a T shows as A). Match by pattern, not by assuming the letter is wrong.
| CC | Typical converter. Both copies are the reference allele, so your BCO1 enzyme handles beta-carotene at full pace. You can generally get enough vitamin A from a normal mix of plant and animal foods. |
| CT | One slow copy. Conversion sits somewhere in the middle. In the human study, carrying the 379V (T) allele was tied to a lower ability to turn beta-carotene into vitamin A, so plant sources work a bit less efficiently for you. |
| TT | Two slow copies. This is the lowest-conversion version of this variant. The 379V allele was linked to a 32% drop in beta-carotene-to-vitamin-A conversion in female volunteers, and unconverted beta-carotene tends to run higher in your blood. Preformed retinol is the more reliable vitamin A source. |
rs12934922 changes amino acid 267 from arginine to serine (R267S). On its own the evidence for a big effect is thin. Where it earns its place is in combination: people carrying the slow alleles of both this SNP and rs7501331 were the worst converters in the study, well below people carrying just one. So read this row alongside the first. Same letter caveat applies: on a 23andMe-style export an A may print as a complementary T, so match by pattern.
| AA | Reference at this spot. No added slowdown from this variant. Your overall conversion still depends on what you carry at rs7501331. |
| AT | One copy of the 267S (T) allele. Minor effect by itself. It matters most when paired with a slow rs7501331 genotype, where the two together stack up. |
| TT | Two copies of the 267S allele. Alone this had little measured effect, but combined with the slow rs7501331 variant it marked the largest conversion drop in the study (about 69% lower). Check both variants together to read your real conversion picture. |
Genotypes are shown order-insensitively and on the forward strand; your own export may print the complementary letters — the meaning is the same.
What the research suggests
If you carry the slow rs7501331 (and especially both slow variants), your BCO1 enzyme converts beta-carotene poorly, so plant beta-carotene is a weak vitamin A source for you. Preformed vitamin A bypasses the BCO1 step entirely and is not affected by your genotype. Keep intake in the normal range rather than high-dose, since retinol is fat-soluble and stores in the body. This is educational; if you take medications or are pregnant or planning to be, talk to a doctor before changing vitamin A intake.
PubMed 19103647 · in female volunteers, the rs7501331 (A379V) variant allele was associated with a 32% lower conversion of beta-carotene to vitamin A, and carrying the slow alleles of both rs7501331 and rs12934922 was associated with a 69% lower conversion plus higher circulating beta-carotene.
Educational only — not medical advice. “General evidence” means the finding is real but the supplement’s benefit isn’t unique to your genotype.
See this matched to your own DNA — free.
Upload your 23andMe or AncestryDNA file and get your actual BCO1 result, plus every other actionable variant — each line cited, your file never stored.
Questions
Does this mean carrots are useless for me?
No. Even slow converters still pull some vitamin A out of beta-carotene, and carotenoids do other useful things in the body on their own. It just means you should not count on plant sources to be your only vitamin A. Mixing in retinol sources, or choosing them when you have the option, covers the gap.
I have the slow version. Should I take a beta-carotene supplement?
Probably not as your main vitamin A strategy, since your enzyme converts it poorly and unconverted beta-carotene just builds up in your blood. Preformed vitamin A is the more reliable choice for you. Don't megadose retinol though; it is fat-soluble and stores in the body, so stay near normal intake unless a clinician tells you otherwise.
Why does the research only mention women?
The human conversion experiment in the foundational paper was done in female volunteers. The enzyme and the gene work the same way in everyone, so the mechanism applies across the board, but that is why you'll see "female volunteers" in the citation.