Forms of B12: What B12 Does Not Have Cyanocobalamin?

November 18, 2025 •

3 min read

Vitamin B12 is an essential nutrient that exists in several distinct forms, but many people are unaware that not all types contain cyanocobalamin. The most common forms found in nature, and increasingly in supplements, are free of this synthetic compound and include methylcobalamin, adenosylcobalamin, and hydroxocobalamin. This distinction is important for individuals seeking more natural sources or who may have specific metabolic needs.

Quick Summary

This article explores natural and synthetic forms of vitamin B12, detailing methylcobalamin, adenosylcobalamin, and hydroxocobalamin as alternatives to the synthetic cyanocobalamin. It covers their different roles, food sources, and varying bioavailability, helping individuals understand their B12 supplement options.

Key Points

Methylcobalamin: A naturally occurring, active form of B12, important for brain and nerve health, and regulating homocysteine levels.
Adenosylcobalamin: The second active form of B12, primarily used in mitochondria for energy metabolism from fats and amino acids.
Hydroxocobalamin: A precursor form that is the standard choice for B12 injections due to its high bioavailability and long retention in the body.
Natural Sources: The non-cyanocobalamin forms of B12 are found naturally in animal products like meat, fish, eggs, and dairy.
Conversion: Unlike synthetic cyanocobalamin, natural forms do not require a conversion step and are immediately available for metabolic use.
Supplement Choice: While both natural and synthetic forms can treat deficiency, natural forms like methylcobalamin may offer advantages for individuals with certain genetic mutations or those preferring bioactive compounds.

Understanding the Different Forms of Vitamin B12

Vitamin B12, or cobalamin, is a vital water-soluble nutrient crucial for red blood cell formation, DNA synthesis, and neurological function. While the synthetic form, cyanocobalamin, is widely used in supplements and fortified foods due to its stability and low cost, it is not the only option available. The body must convert cyanocobalamin into the two active coenzyme forms, methylcobalamin and adenosylcobalamin, before it can be utilized. The naturally occurring forms bypass this conversion, offering a more direct route for the body's metabolic pathways.

The Natural Forms of Vitamin B12 (Non-Cyanocobalamin)

There are three primary forms of B12 that do not contain cyanocobalamin and are naturally present in animal-based foods and human physiology:

Methylcobalamin (MeCbl): This is one of the two active coenzyme forms used by the body. It is important for the methylation cycle, essential for nerve cells, protein metabolism, and converting homocysteine to methionine. This supports cardiovascular and nerve health.
Adenosylcobalamin (AdoCbl): The second active coenzyme form, adenosylcobalamin, is mainly in cell mitochondria. It is a cofactor in converting methylmalonyl-CoA to succinyl-CoA, a key step in energy production from fats and proteins.
Hydroxocobalamin (OHCbl): This natural precursor is formed during the body's detoxification of cyanocobalamin. It's often used for injectable B12 due to its high bioavailability and long retention. Hydroxocobalamin is considered better for those with certain genetic disorders or cyanide exposure.

Why Different Forms Matter

Choosing a B12 form can be important, especially for those with specific health needs or diets. People with certain genetic mutations, such as MTHFR variants, may process synthetic cyanocobalamin less effectively. Natural forms are sometimes preferred by practitioners for their direct metabolic use and better retention.

Comparison of B12 Forms


Feature	Methylcobalamin	Adenosylcobalamin	Hydroxocobalamin	Cyanocobalamin
Origin	Natural	Natural	Natural	Synthetic
Active Coenzyme	Yes	Yes	No (precursor)	No (precursor)
Bodily Role	Methylation reactions, brain and nerve health, homocysteine regulation	Mitochondrial energy production, fat and amino acid metabolism	Cyanide detoxification, precursor to active forms	Precursor converted by the body into active forms
Retention in Body	High retention	High retention	High retention, long-lasting	Lower retention, higher urinary excretion
Stability	Less stable when exposed to light and heat	Less stable than cyanocobalamin	More stable than methylcobalamin/adenosylcobalamin	Highly stable
Common Use	Bioactive supplements, nerve support	Specialized supplements, energy metabolism	Injections for severe deficiencies, antidote for cyanide poisoning	Standard supplements, fortified foods

Natural Sources of B12 Without Cyanocobalamin

Naturally occurring B12 is found mostly in animal products, primarily as adenosylcobalamin and hydroxocobalamin. Good natural sources include:

Organ Meats: Beef liver is a rich source.
Meat and Poultry: Beef, lamb, and chicken are good sources.
Fish and Shellfish: Clams, salmon, tuna, and mackerel are particularly high in B12.
Dairy Products: Milk, cheese, and yogurt provide B12 for vegetarians.
Eggs: The yolk is a good source.

Vegans and many vegetarians need fortified foods or supplements because plants don't produce B12. Fortified options like nutritional yeast and plant-based milks offer vegan-friendly B12, though the specific form varies.

Conclusion: Selecting the Right B12

Cyanocobalamin is a stable, cost-effective supplement form, but not the only one. Natural, active methylcobalamin and adenosylcobalamin offer direct metabolic use, while hydroxocobalamin is a high-retention option for injections. The best choice depends on individual needs, diet, and genetics. For most healthy people, all forms work, but those with absorption issues or a preference for natural options may benefit from methylcobalamin or a mix of natural types. Consult a healthcare provider to find the most suitable B12 form. For more on B12's role, see the NIH Office of Dietary Supplements.

Frequently Asked Questions

Cyanocobalamin is a synthetic form of vitamin B12 created in a lab, while methylcobalamin is a natural, active coenzyme form found in food and used directly by the body.

Naturally occurring forms of B12 found in animal products are primarily adenosylcobalamin and hydroxocobalamin. Methylcobalamin is also a natural form found in food sources.

For most people, all forms of B12 can effectively treat a deficiency. However, some studies suggest that natural forms like methylcobalamin have better retention in the body, and they are preferred by people with certain genetic variations.

Cyanocobalamin is the most common form of B12 in supplements because it is the most stable and cost-effective to produce.

People with specific genetic mutations affecting B12 metabolism, such as MTHFR variants, may benefit from active forms like methylcobalamin. Individuals with conditions affecting B12 absorption or those who prefer natural ingredients may also choose non-cyanocobalamin options.

B12 injections can contain either cyanocobalamin or hydroxocobalamin. In some regions, like the UK, hydroxocobalamin is preferred for injections because it remains in the body longer.

Since B12 is scarce in plant foods, vegans and vegetarians must rely on fortified foods like nutritional yeast, fortified plant milks, and fortified cereals, or use supplements. Natural methylcobalamin supplements are also available for vegan consumption.