What Vitamin is Found in Fermented Foods?

October 30, 2025 •

5 min read

According to a 2025 review, microorganisms in fermented foods can increase levels of vitamins K2, B2, B9, and B12. This makes fermented foods an important source of nutrients, especially for those on plant-based diets, as the fermentation process enriches certain vitamins that are often limited in unfermented plant-based foods.

Quick Summary

Fermented foods, created through microbial action, are a natural source of beneficial vitamins, including vitamin K2 and several B vitamins such as B12 and folate. The specific vitamin content depends on the microbes involved, the ingredients, and the fermentation process. These foods contribute to overall nutritional intake and support gut health.

Key Points

B Vitamins: Fermented foods can be a source of various B vitamins, including B2, B9, and B12, with levels depending on the microbial strains used.
Vitamin K2: Many fermented foods, especially natto and certain cheeses, are excellent sources of vitamin K2, which is important for bone and heart health.
Enhanced Bioavailability: The fermentation process can increase the body's ability to absorb nutrients by breaking down compounds like phytic acid.
Source of Probiotics: The live cultures in fermented foods contribute to a healthy gut microbiome, which is linked to a range of health benefits.
Variable Content: The specific vitamin content can vary depending on the microorganisms, starter cultures, and food matrix used in the fermentation.
B12 for Vegans: While B12 is typically from animal sources, some plant-based fermented foods can be fortified with B12 using specific bacteria, though levels can be inconsistent in naturally fermented versions.

The Fermentation Process and Vitamin Enrichment

Fermentation is an ancient food preservation technique that uses microbes like bacteria, yeast, and molds to convert carbohydrates into organic acids, alcohols, or gases. This process not only preserves food and enhances flavor but also creates or increases the bioavailability of certain nutrients, most notably specific vitamins.

Microbial Players in Vitamin Synthesis

Different microorganisms are responsible for producing different vitamins during fermentation. For instance, Propionibacterium freudenreichii is well known for synthesizing vitamin K2 (menaquinone) in Swiss-type cheeses and can also be used to fortify other foods with vitamin B12. Other lactic acid bacteria (LAB), like Lactobacillus species, can produce various B vitamins.

Vitamin K2 (Menaquinones): Primarily synthesized by bacteria, vitamin K2 is found in high concentrations in certain fermented foods. The length of the menaquinone side chain varies based on the bacteria, affecting its bioavailability.
B Vitamins: Many B vitamins are produced during fermentation, including B2 (riboflavin), B9 (folate), and B12 (cobalamin). However, the consistency and amount can be highly dependent on the starter cultures and ingredients.
Enhanced Bioavailability: Fermentation can break down complex compounds like phytic acid in grains, which can block mineral absorption. This process increases the bioavailability of nutrients, making them easier for the body to absorb.

Key Vitamins Found in Fermented Foods

Fermented foods are a valuable dietary source for several vitamins, offering a natural and often more bioavailable form compared to some synthetic alternatives.

Vitamin B12: A Unique Source for Plant-Based Diets

Vitamin B12 is typically found in animal products, making it a critical nutrient for vegetarians and vegans to monitor. While many plant-based fermented foods contain B12, the amounts can vary significantly and are often due to specific microbial strains or, in some cases, contamination.

Fortified Plant Foods: Research is ongoing into biofortifying plant-based fermented foods with B12 using specific bacteria like Propionibacterium freudenreichii. For example, soy yogurt and lupin tempeh can be enriched with significant amounts of B12 through co-fermentation.
Traditional Foods: Some traditional fermented plant foods, such as certain kimchi, have been observed to contribute to B12 intake in some populations, although the levels can be inconsistent and may not meet daily requirements alone.

Vitamin K2: Essential for Bone and Heart Health

Vitamin K2 is a crucial nutrient for proper calcium utilization, supporting bone mineralization and preventing arterial calcification. Fermented foods are a primary source, and the specific menaquinone (MK) type depends on the product.

Natto: This Japanese fermented soybean food is exceptionally rich in MK-7, a highly bioavailable and potent form of vitamin K2.
Fermented Dairy: Cheeses like Jarlsberg and Gouda contain MK-9, produced by the starter bacteria Propionibacterium freudenreichii.
Kefir: This fermented milk drink is also a notable source of vitamin K2.

B-Vitamins (Beyond B12)

In addition to B12, the fermentation process can boost other B vitamins:

Folate (B9): Fermentation, particularly in dairy and some vegetables, can increase folate content. Certain lactic acid bacteria are particularly adept at this.
Riboflavin (B2): Produced by some lactic acid bacteria, riboflavin levels can be elevated in fermented foods like certain yogurts.

Fermented Foods: A Comparison of Vitamin Content


Fermented Food	Primary Vitamins Found	Key Microbes Involved	Notes on Production and Content
Natto	Vitamin K2 (MK-7), Probiotics	Bacillus subtilis var. natto	Exceptionally high in K2; requires specific bacteria for production.
Kefir	Vitamin B12, Vitamin K2, Probiotics	Lactobacillus, yeast, other bacteria	Vitamin content can vary based on milk source and fermentation.
Sauerkraut/Kimchi	Vitamin C, B vitamins, Probiotics	Lactic acid bacteria	Vitamin C levels can increase. B vitamin content varies by starter culture and process.
Fermented Cheese	Vitamin K2 (MK-9), Probiotics	Propionibacterium freudenreichii (Swiss-type)	Specific K2 forms are related to bacterial activity during cheese making.
Tempeh	Potentially B12 (from co-fermentation)	Rhizopus fungus, potentially B12-producing bacteria	B12 is not inherent; depends on fortification with specific bacteria.
Yogurt	B Vitamins (B2, B9), B12 (if fortified)	Lactic acid bacteria (Lactobacillus, Streptococcus)	B12 levels are often enhanced via starter cultures or fortification.

Factors Influencing Vitamin Levels in Fermented Foods

Several factors can influence the vitamin levels found in fermented foods, making their nutritional profiles somewhat variable:

Starter Culture and Microbial Strains: The specific bacterial or yeast strains used for fermentation are the primary drivers of vitamin synthesis. Different strains have different capacities for producing vitamins, so a product's nutrient content can depend heavily on the cultures used.
Substrate (Ingredients): The starting ingredients provide the raw materials for the microbes. For example, soy is used for natto, while dairy is used for cheese and kefir. The nutrient composition of the base ingredient influences what and how many vitamins can be produced.
Fermentation Conditions: Environmental factors such as temperature, pH levels, and fermentation duration can impact microbial growth and, consequently, vitamin production. For instance, longer fermentation can lead to higher vitamin yields.
Contamination: In some traditionally or spontaneously fermented products, the presence of B12-producing bacteria is due to environmental or processing factors, which can lead to inconsistent and unreliable vitamin levels. For this reason, manufactured products with intentionally added cultures for biofortification are often more reliable.
Processing: Heat and other post-fermentation treatments can destroy vitamins, especially if the live microorganisms are eliminated. For probiotics to be beneficial, the microorganisms must remain viable throughout the shelf life of the product.

Conclusion: A Natural Boost to Your Diet

Fermented foods are a fascinating and delicious example of how microbial action can enhance food's nutritional value. They are particularly known for their contributions of vitamin K2 and various B vitamins, especially B12 in certain fortified or culturally prepared varieties. The presence of these vitamins, along with beneficial probiotic bacteria, underscores the health-promoting reputation of these foods. While vitamin content can be variable, intentionally cultivated products offer a more reliable nutritional boost. Incorporating a variety of fermented foods into your diet is a simple way to reap the benefits of this ancient and healthful practice.

More Than Just Vitamins

In addition to providing key vitamins, the live cultures in many fermented foods can help maintain a balanced gut microbiome. A healthy gut has been linked to numerous benefits, including improved digestion, strengthened immune function, and even better mood. For those seeking to enhance their intake of specific vitamins naturally, fermented foods offer a delicious and effective pathway. As interest in gut health and natural nutrition grows, the importance of these microbial-rich foods becomes ever clearer.

Fermented foods for better gut health - Harvard Health

Frequently Asked Questions

Fermented foods that may contain vitamin B12 include some fortified soy products like certain tempeh varieties and soy yogurt made with B12-producing bacteria, as well as some types of kimchi and fermented cheeses. However, the B12 content in non-fortified plant-based fermented foods can be inconsistent and unreliable.

Vitamin K1 is primarily found in leafy green vegetables, while vitamin K2 is mostly produced by bacteria during fermentation and found in fermented foods and certain animal products. Vitamin K2 is particularly important for bone and cardiovascular health.

Not all forms of cobalamin (B12) produced by bacteria are bioavailable for humans. Some fermented foods, particularly certain algae and unfortified tempeh, may contain inactive analogues of B12 that are not useful to the human body and can interfere with the absorption of active B12.

Yes, some fermented foods, particularly those involving certain strains of lactic acid bacteria, can contain increased levels of vitamin C. For instance, raw, fermented red cabbage has been shown to have a higher vitamin C content than its unfermented counterpart.

While fermented foods are a great source of beneficial vitamins and probiotics, they shouldn't be the sole source for your daily vitamin needs. The vitamin content can be inconsistent depending on the food, microbe strains, and fermentation process. A varied diet, potentially supplemented with fortified foods or supplements, is recommended for consistent vitamin intake.

No, not all fermented foods contain live and beneficial probiotics. Some fermentation methods, like those used for wine, do not result in a significant probiotic presence. Additionally, pasteurization or cooking can destroy the live microorganisms in fermented products.

To maximize vitamin intake, choose a variety of fermented foods. Opt for products with specific starter cultures known to produce vitamins, such as natto for vitamin K2 or certain fortified plant yogurts for B12. Consume raw or unpasteurized fermented foods to ensure the live cultures remain intact.