Can Probiotics Increase Vitamin B12? An In-Depth Look at the Evidence

December 12, 2025 •

4 min read

Some animal and in-vitro studies have shown that certain probiotic strains can increase the absorption of B vitamins, including B12, by a significant percentage. But can probiotics increase vitamin B12 levels in humans effectively, and how does this mechanism work in the complex human gut? This question requires a closer examination of microbial activity and nutrient absorption dynamics.

Quick Summary

Certain probiotic strains can synthesize vitamin B12 or enhance its absorption by improving gut health. The bioavailability of this microbially-produced B12 to the human body is still being researched, as it is often synthesized in a different part of the intestine from where it is absorbed. The specific strains and overall gut environment play a crucial role in the outcome.

Key Points

Synthesis vs. Absorption: Probiotics can either synthesize B12 in the gut or improve the absorption of B12 from dietary sources, but the bioavailability of microbially-produced B12 to the human host is uncertain.
Enhanced Absorption: A healthy gut microbiome, supported by probiotics, improves the efficiency of nutrient absorption in the small intestine, benefiting the uptake of B12.
Strain-Specific Effects: The ability to produce or enhance B12 depends on the specific probiotic strain; some strains, like certain Lactobacillus and Bifidobacterium, show more promise than others.
Not a Replacement for Treatment: Probiotics should not be considered a treatment for a diagnosed B12 deficiency, which typically requires a direct supplement or injection.
Complex Interactions: The effects of probiotics on B12 levels are influenced by individual gut microbiota composition, making consistent results in human studies challenging.
Location Matters: The synthesis of B12 often occurs in the large intestine, while absorption happens primarily in the small intestine, creating a bioavailability challenge for human benefit.
Combined Approach: The most effective strategy involves ensuring sufficient B12 intake through diet or supplements while using probiotics to support overall gut health.

Understanding Vitamin B12 and Probiotics

Vitamin B12, or cobalamin, is a crucial nutrient for nerve function, red blood cell formation, and DNA synthesis. The human body cannot produce B12, and it is primarily obtained from animal-based foods, fortified products, and supplements. A deficiency can lead to severe neurological and hematological issues. Probiotics are live microorganisms that confer health benefits when consumed in adequate amounts, primarily by supporting the balance of the gut microbiome. The relationship between probiotics and vitamin B12 is complex, involving both the potential for bacterial synthesis and improved host absorption.

The Mechanisms: Synthesis vs. Absorption

The influence of probiotics on vitamin B12 is understood through two primary mechanisms: microbial synthesis and enhanced absorption. While these are often discussed together, they operate in different parts of the digestive system and have varying implications for human health.

Synthesis by Gut Bacteria

It is well-established that bacteria are the sole producers of vitamin B12 in nature. Research has identified several probiotic strains capable of producing B vitamins, including B12, during fermentation. These include certain species of Lactobacillus and Bifidobacterium, as well as other strains like Cetobacterium somerae. However, a significant challenge for human benefit is the location of this synthesis. Most of the vitamin B12 produced by gut bacteria occurs in the large intestine, while the body's primary absorption site for B12 is the small intestine. This anatomical separation means that much of the B12 synthesized in the large intestine is not absorbed by the body and may instead be used by other gut microbes. Furthermore, some bacteria can produce inactive B12 analogues (cobamides) that actually compete with and inhibit the absorption of the active form.

Enhanced Absorption

A healthier gut environment, supported by a balanced microbiome, is a key factor in improving the body's ability to absorb nutrients, including vitamin B12 from dietary sources and supplements. Probiotics contribute to better gut health by:

Improving the intestinal barrier: Strengthening the gut lining can enhance nutrient uptake and reduce inflammation.
Balancing gut flora: A healthy balance of microorganisms helps optimize digestive function.
Producing enzymes: Some strains can help break down food, releasing bound vitamins like B12 for absorption.

Therefore, even if probiotics don't produce B12 that the body can use, they can still help the body more effectively utilize the B12 it gets from other sources. This is particularly important for individuals with underlying gastrointestinal conditions that impair nutrient absorption.

Comparison: Direct B12 Supplement vs. Probiotics

For those with confirmed B12 deficiency, a direct B12 supplement is the most reliable treatment. Probiotics serve a different, complementary role. Here is a comparison:


Feature	Direct B12 Supplement	Probiotic Supplementation
Primary Function	Provides a guaranteed dose of active B12 to correct deficiency.	Supports overall gut health and may enhance nutrient absorption indirectly.
Bioavailability	High, especially with sublingual or injection methods; reliable.	Variable, depends on strain and gut environment; not a reliable primary source.
Best for Deficiencies?	Yes, the gold standard for treatment.	No, should not be used as a substitute for B12 therapy.
Mechanism	Delivered B12 is absorbed directly in the small intestine.	Enhances overall gut function, which can improve absorption of B12 from other sources.
Primary Benefit	Replenishing deficient B12 levels.	Promoting a balanced, healthy gut microbiome.

Which Probiotic Strains Matter for B12?

Not all probiotics are created equal. The effect on B12 levels is highly strain-specific. For example, some studies suggest that certain Lactobacillus and Bifidobacterium species can produce B12, or at least enhance its uptake. The strain Lactobacillus reuteri is known to synthesize B12, but some research indicates it might also produce inactive analogues. In contrast, some evidence points to the potential of strains like Lactobacillus plantarum to aid in B12 production. For definitive effects on human B12 status, more research is needed to identify which specific strains offer the most benefit without contributing to analogue production in the human digestive tract.

How to Maximize the Benefits of Probiotics

To leverage the potential benefits of probiotics for nutrient absorption, consider the following strategies:

Choose targeted products: Look for probiotic supplements or fortified foods containing specific strains known to support gut health and, potentially, B-vitamin metabolism, such as certain Lactobacillus or Bifidobacterium species.
Include fermented foods: Incorporate a variety of fermented foods like yogurt, sauerkraut, and kimchi into your diet, as these naturally contain probiotics. Some fermented foods, particularly those bio-fortified with B12-producing strains, can be a valuable source.
Pair with B12 sources: Take probiotics in conjunction with a diet rich in B12 from animal products, fortified cereals, or a B12 supplement to ensure there is B12 present in the small intestine for absorption.
Consult a professional: If you have concerns about B12 deficiency, consult a healthcare provider. While probiotics can support general gut health, they are not a replacement for medical treatment of a clinically diagnosed deficiency.

Conclusion

To answer the question, can probiotics increase vitamin B12, the answer is nuanced. While certain probiotic bacteria can produce vitamin B12, the synthesis often occurs in the large intestine, limiting its bioavailability to humans. The more reliably demonstrated effect is the enhancement of B12 absorption through a healthier gut microbiome, which is a secondary effect of taking probiotics. For individuals with a diagnosed B12 deficiency, relying solely on probiotics is not a recommended or effective strategy. The best approach involves a combination of a balanced diet rich in B12 sources, appropriate supplementation if needed, and the complementary support of targeted probiotics to optimize overall digestive function and nutrient absorption. Further research is necessary to fully understand the specific strains and conditions that lead to clinically significant increases in B12 levels in humans.

The National Institutes of Health provides comprehensive information on vitamin B12 deficiency and its treatment, emphasizing the importance of addressing the root cause, which often requires direct supplementation rather than relying on microbial synthesis alone. NIH Vitamin B12 Fact Sheet

Frequently Asked Questions

No, probiotics alone cannot be relied upon to cure a diagnosed vitamin B12 deficiency. A clinical deficiency typically requires direct supplementation or injections, as the amount and bioavailability of B12 from probiotics is unreliable.

While research is ongoing, some studies suggest certain species within the Lactobacillus and Bifidobacterium families may contribute to B12 synthesis or improved absorption. However, individual results can vary, and more human trials are needed to confirm the most effective strains.

No, not all probiotic strains have the capacity to produce vitamin B12. Even among strains that do, the amount produced and its absorbability are highly variable. Some strains may even produce inactive B12 analogues.

Probiotics can improve the overall health of the gut microbiome. A healthier gut environment with less inflammation and a stronger intestinal barrier is more efficient at absorbing nutrients, including B12, from food and supplements.

The usefulness of B12 produced by gut bacteria is highly debated. Because most production occurs in the large intestine and absorption happens in the small intestine, the B12 is often not bioavailable to the human host. It is instead primarily used by the bacteria themselves.

Yes, taking B12 supplements and probiotics together is generally considered safe and may even be beneficial. The probiotics can help optimize the gut environment for better overall nutrient absorption, complementing the B12 from the supplement.

Yes, some fermented foods, like certain fortified yogurts or sourdough bread, have been shown to contain B12 due to the activity of probiotic strains. However, the amounts can be inconsistent and should not be relied upon to treat a deficiency.