The association is established; acting on it is not advised
Two common variants in the enzyme that turns plant beta-carotene into usable vitamin A — carriers of both convert 69% less efficiently, which is a real reason "eat more carrots" does not work the same for everyone.
Vitamin A can come from two different places in the diet: preformed retinol (animal sources — liver, eggs, dairy) or provitamin A carotenoids like beta-carotene (plant sources — carrots, sweet potato, leafy greens), which the body has to convert. The enzyme that does the converting is BCO1, and it is not equally efficient in everyone.
A 2009 study screened the entire coding region of BCO1 and found two common variants: R267S (rs12934922), carried by 42% of the studied population, and A379V (rs7501331), carried by 24%. In the lab, the double-variant enzyme had 57% less catalytic activity (P<0.001) than the typical form.
Tested in female volunteers given a measured dose of beta-carotene, the biochemistry held up as a real, whole-body effect. Carriers of A379V alone converted beta-carotene 32% less efficiently (P=0.005) and had 160% higher fasting beta-carotene levels than non-carriers — the unconverted pigment building up in the blood instead. Carriers of both variants together converted 69% less efficiently (P=0.001), with 240% higher fasting beta-carotene.
Roughly 45% of people are "low responders" to dietary beta-carotene for reasons that include but are not limited to this gene, and no guideline currently tests BCO1 before giving vitamin A advice. For someone relying heavily on plant sources — a strict vegan, for instance — a poor-converter genotype is a real reason blood retinol might run lower than the diet alone would suggest; the practical answer is a blood test or a preformed-retinol source, not guessing from genotype alone. This page is unrelated to this site's beta-carotene and vitamin E page, which covers a different question entirely: whether high-dose supplements of these raise or lower cancer risk in smokers. That trial evidence applies regardless of BCO1 genotype.
Vitamin A is a nutrient needed for vision, immune function and skin health, obtained either directly from animal sources or converted by the body from plant beta-carotene, as in carrots. Two common variants affect how efficiently that conversion happens.
Not by itself — no guideline tests BCO1 before giving vitamin A advice. It is a real reason blood retinol might run low on a plant-heavy diet, best confirmed with an actual blood test.
No — that page covers whether high-dose supplements raise or lower cancer risk in smokers. This page covers a completely different question: how efficiently your body converts dietary beta-carotene into usable vitamin A in the first place.
Common — 42% of the studied population carried R267S and 24% carried A379V. Around 45% of people are classified as "low responders" to dietary beta-carotene for reasons that include but are not limited to these two variants.
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Vitamin A (beta-carotene conversion). MyGeneLog™. https://www.mygenelog.com/supplements/vitamin-a
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