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Vitamin B12 and Your FUT2 Gene: What You Need to Know

Vitamin B12 is a water soluble nutrient that supports nerve health, brain function, red blood cell production, and DNA synthesis. Many people get B12 from animal foods such as meat, fish, eggs, and dairy. Plant based eaters need fortified foods or supplements to meet requirements. Your FUT2 gene can influence how well your body absorbs B12 by shaping secretor status and the mix of bacteria living in your gut. Variants in FUT2 can reduce enzyme function, which may lower B12 absorption and increase risk of deficiency.

How FUT2 Affects B12 Absorption

The FUT2 gene makes an enzyme that adds specific sugar molecules to the surfaces of mucosal cells and to secreted fluids. This process helps determine secretor status and influences which bacteria thrive in the gut. Certain gut bacteria contribute to B12 synthesis or help free B12 from food so the body can absorb it. When FUT2 function is reduced, the gut environment may shift in ways that make B12 absorption less efficient. This effect is more important when dietary intake of B12 is low, such as on vegetarian or vegan diets.

Signs and Risks of Low B12

  • Fatigue or low energy
  • Numbness or tingling in hands and feet
  • Difficulty concentrating or memory changes
  • Pale or jaundiced skin from red blood cell changes
  • Glossitis or mouth soreness

If you notice these signs, consider checking B12 levels with your healthcare provider. B12 deficiency can develop slowly and is reversible if detected and treated early.

Diet, Supplements, and Lifestyle Recommendations

The following practical steps can help support healthy B12 levels and overall gut health.

  • Dietary sources: Include animal-based foods if you eat them. Prioritize lean meats, fish, shellfish, eggs, and dairy. For those who avoid animal foods, choose fortified plant milks, nutritional yeast, and fortified cereals.
  • Supplements: Consider a B12 supplement if dietary intake may be insufficient. Options include daily cyanocobalamin or methylcobalamin tablets, or higher dose oral supplements if needed. Sublingual or intramuscular B12 may be recommended by a clinician for significant deficiency.
  • Probiotics and prebiotics: Support a diverse gut microbiome with probiotic-rich foods like yogurt and kefir if tolerated, and prebiotic fiber from onions, garlic, leeks, asparagus, bananas, and whole grains.
  • Fiber and whole foods: A fiber rich diet supports gut bacteria that contribute to overall gut health. Aim for a variety of vegetables, fruits, legumes, nuts, seeds, and whole grains.
  • Limit factors that impair absorption: Chronic alcohol use, long term use of proton pump inhibitors, metformin use, and some gastrointestinal disorders can reduce B12 absorption. Talk with your provider about medication impacts.
  • Monitoring: If you are at risk due to diet, medication, gastrointestinal conditions, or a family history of absorption issues, arrange periodic B12 testing with your healthcare provider. Tests often include serum B12 and may include methylmalonic acid and homocysteine when more precision is needed.

Testing and Follow Up

Measure B12 if you have symptoms or risk factors. Typical tests include total serum B12. If results are borderline, clinicians often check methylmalonic acid to detect early tissue deficiency. If you are diagnosed with deficiency, your healthcare provider will guide the best treatment plan which may include oral high dose B12 or injections depending on severity and absorption issues.

Genetic Interpretation for rs601338 (FUT2)

Two effect alleles (GG) — Reduced FUT2 function

If you have the GG genotype for rs601338 you carry two copies of the effect allele associated with reduced FUT2 enzyme function. This change can alter secretor status and the composition of your gut microbiome. The result may be less efficient Vitamin B12 absorption even when dietary B12 is present. Your risk of B12 deficiency is higher compared with people who have full FUT2 function, particularly if you follow a vegetarian or vegan diet or take medications that impair absorption. Recommended actions include increased attention to dietary B12, regular monitoring of B12 levels, and consideration of supplementation. Support your gut microbiome with probiotics, prebiotic fibers, and a varied diet rich in whole plant foods. Speak with your healthcare provider about testing strategies and supplement dosing if levels are low.

One effect allele (AG) — Moderately reduced FUT2 function

If you have the AG genotype for rs601338 you carry one copy of the effect allele. This genotype is associated with a moderate reduction in FUT2 enzyme function and a potential small increase in risk for decreased B12 absorption. Many people with this genotype absorb B12 normally with an adequate diet, but risk increases if dietary intake is low or if other absorption challenges are present. To protect your B12 status, prioritize reliable B12 sources such as animal foods or fortified foods, consider a low dose supplement as a safety measure, and maintain gut health through fiber and probiotic rich foods. Test B12 levels if you have symptoms or are in a higher risk group.

Zero effect alleles (AA) — Typical FUT2 function

If you have the AA genotype for rs601338 you carry two copies of the non effect allele and are associated with normal FUT2 enzyme function. This genotype supports typical secretor status and a gut environment that facilitates normal B12 absorption. With a balanced diet that includes reliable B12 sources, your body is generally well equipped to maintain adequate B12 levels. If you follow a plant based diet, continue to use fortified foods or supplements to ensure intake. Routine annual wellness testing may be appropriate if other risk factors arise.

Practical Checklist

  • Review your diet for reliable B12 sources or fortified foods.
  • Consider a daily B12 supplement if you are vegetarian, vegan, or have absorption risks.
  • Support gut health with prebiotic fibers, probiotic foods, and a varied whole food diet.
  • Discuss medications or conditions that affect absorption with your healthcare provider.
  • Arrange B12 testing if you have symptoms or ongoing risk factors.

PlexusDx provides educational information about genetic predispositions only. This content does not constitute medical advice. Always consult with your healthcare provider before making changes to your diet, supplements, or medical care. Your provider can interpret genetic information in the context of your personal health history, medications, and lab results to recommend appropriate testing or treatment.