Vitamin B12 sparks endless debate about diet. Is it only in animal foods? Do we get it from soil? Why do some people have low B12 despite eating plenty of meat, eggs, or dairy? Let’s cut through the myths and look at the science — including a gene called FUT2 that affects how your body handles this vitamin.
MYTH 1: ANIMALS MAKE VITAMIN B12
Animals don’t make vitamin B12, and neither do humans. Only bacteria and archaea produce it. Animals accumulate B12 by consuming bacteria directly or through contaminated food and water. That’s why liver, meat, fish, eggs, and dairy contain B12 — animals are carriers, not producers.
MYTH 2: WE CAN JUST GET B12 FROM SOIL OR PLANTS
This is half-true but misleading. In theory, unwashed vegetables grown in rich, bacteria-filled soil might contain B12. In practice, modern farming and hygiene remove most of it. Not all soil bacteria make the human-useable form, so plant foods remain unreliable sources.
WHY B12 IS TRICKY
Vitamin B12 is essential for producing red blood cells, protecting nerves, and maintaining the smooth functioning of DNA synthesis. Deficiency can lead to fatigue, memory problems, mood changes, anaemia, and long-term neurological damage. However, even people who consume animal products can sometimes become deficient. One reason? Genetics.
THE FUT2 GENE CONNECTION
FUT2 is a gene that influences B12 absorption and circulation. One common variant, rs602662, affects how well your digestive system absorbs B12 from food.
People with certain versions of this variant often exhibit lower blood B12 levels even if their diet appears adequate. It doesn’t necessarily mean they’re deficient in a clinical sense, but it does suggest their metabolism of B12 is less efficient.
WHY THIS MATTERS
- Vegetarians and vegans: Since B12 isn’t naturally found in plants, they rely on fortified foods or supplements. Genetic variants, such as FUT2 rs602662, can make it even more crucial to monitor B12 status.
- Meat-eaters: Eating steak isn’t a guarantee. Genes or gut health can still cause a deficiency by interfering with absorption.
- Health monitoring: Simple blood tests can reveal whether you’re at risk. In some cases, supplementing with methylcobalamin or cyanocobalamin (the most common B12 supplement forms) can bypass the absorption bottleneck.
So if you’ve ever felt tired, foggy, or wondered why your B12 levels look off despite eating “enough,” it’s not just about what you eat. It could be about how your body handles it, and your genes might be part of the story.
References:
Tanwar, V. S., Chand, M. P., Kumar, J., Garg, G., Seth, S., Karthikeyan, G., & Sengupta, S. (2013). Common variant in FUT2 gene is associated with levels of vitamin B12 in Indian population. Gene, 515(1), 224-228.
Hazra A et al. Common variants of FUT2 are associated with plasma vitamin B12 levels. Nature Genetics. 2008 Oct;40(10):1160-2.