Does the FUT2 gene in my DNA file affect my vitamin B12?
It affects how a total B12 blood test reads more than how much B12 your body can use. Non-secretors (A A at rs601338) tend to have higher total serum B12, but the extra sits on a carrier protein the liver takes up, while the bioactive form, holo-transcobalamin, is not influenced.
What to look for in your file
Search your raw data for rs601338 (chromosome 19). Files report it as A and G. The A allele is the FUT2 "non-secretor" variant, known as W143X (also numbered Trp154Ter), which truncates the enzyme.
| Your letters | Associated with |
|---|---|
| G G | Secretor. Total serum B12 may read slightly lower than a non-secretor's, with no difference in bioactive B12. |
| A G | Secretor (one working copy is enough). Same as G G for B12 readings. |
| A A | Non-secretor. Tends toward higher total serum B12, because more B12 is bound to haptocorrin; bioactive B12 is not affected. |
A genome-wide study in the Nurses' Health Study first linked FUT2 with plasma B12; women homozygous for the associated allele had higher B12, and that allele is in strong linkage with the W143X non-secretor variant (PMID 18776911). A later NIH study split total B12 into its two carrier-bound fractions: B12 bound to haptocorrin stayed strongly associated with rs601338, while transcobalamin-bound B12 (holoTC, "the bioactive form… taken up by all tissues") was not influenced (PMID 29040465).
How common is each result?
| Population group | A letter | A A non-secretor (estimated) |
|---|---|---|
| African | 49.1% | 24% |
| Admixed American | 34.1% | 12% |
| East Asian | 0.4% | under 0.1% |
| European | 44.1% | 19% |
| South Asian | 28.3% | 8% |
Allele frequencies: 1000 Genomes phase 3 via Ensembl, read 2026-10-23. Genotype shares are Hardy–Weinberg estimates.
All three results are common in most groups. In East Asian participants this particular A allele is almost absent, so this one marker says little about secretor status there; other FUT2 variants are not covered by it.
Limits
- This genotype does not tell you whether you are low in B12; only a blood test interpreted by a clinician can.
- One marker in one gene; other FUT2 variants and other genes also influence B12 readings.
- Not a diagnosis. If you have symptoms or a borderline result, a clinician can interpret it; the study above notes that total B12 has substantial false-positive and false-negative rates as a test.
What to do with it, in food terms
- Your FUT2 result does not change how much B12 you need to eat.
- B12 comes from animal foods (fish, meat, eggs, dairy) and from fortified foods. If you eat few or no animal foods, B12-fortified foods matter whatever your genotype.
- If you are an A A non-secretor and a total B12 test looks reassuringly high, remember part of that reading is haptocorrin-bound B12. Mention your secretor status if B12 is being checked.
References
- Hazra A et al. Common variants of FUT2 are associated with plasma vitamin B12 levels. Nat Genet 2008;40:1160–2. PMID 18776911
- Velkova A et al. The FUT2 secretor variant p.Trp154Ter influences serum vitamin B12 concentration via holo-haptocorrin, but not holo-transcobalamin. Hum Mol Genet 2017;26:4975–88. PMID 29040465
- 1000 Genomes Project phase 3 allele frequencies for rs601338, via Ensembl.
Genomeats reads this marker on your phone — nothing is uploaded. Full write-ups for this trait are free. Coming soon to the App Store.