What Is Natural B12 Called? Unpacking the Forms of Cobalamin

November 24, 2025 •

3 min read

Vitamin B12, or cobalamin, is naturally found in animal products like meat, fish, and dairy, and is produced by certain bacteria. While the collective name for this family of compounds is cobalamin, the specific compounds considered natural B12 are primarily methylcobalamin and adenosylcobalamin, which the body can use directly.

Quick Summary

The active, natural forms of B12 are called methylcobalamin and adenosylcobalamin. This vitamin, also known as cobalamin, is obtained from animal products or fortified foods, with different forms having varying bioavailability.

Key Points

Cobalamin: The collective name for all forms of vitamin B12 due to their central cobalt atom.
Active Natural Forms: The two primary active forms of B12 are methylcobalamin and adenosylcobalamin, which the body uses directly.
Methylcobalamin Functions: This form is crucial for brain health, nerve function, and the vital process of methylation.
Adenosylcobalamin Functions: This form is essential for mitochondrial energy metabolism and cellular energy production.
Cyanocobalamin: A synthetic form of B12, manufactured for supplements and fortified foods, that requires conversion by the body.
Food Sources: Natural B12 is found in animal products like meat, fish, eggs, and dairy, as well as fortified foods containing the synthetic version.
Absorption: Absorption decreases with age, and specific populations like older adults or those with certain gene mutations may benefit from different forms.

What is a Cobalamin?

All forms of vitamin B12 are known collectively as cobalamins. They share a central cobalt atom, and different attached molecules define the specific form. The two main forms active in the human body are methylcobalamin and adenosylcobalamin.

The Active, Natural Forms of B12

Methylcobalamin

Methylcobalamin is one of the two active, coenzyme forms of B12. It is vital for the methylation cycle, supporting detoxification, DNA repair, neurotransmitter creation, and converting homocysteine to methionine, which benefits cardiovascular health. Found in animal foods and supplements, it's directly usable by the body.

Adenosylcobalamin

Adenosylcobalamin is the other active natural form, working with methylcobalamin. It functions primarily in mitochondria, crucial for metabolizing fats and amino acids for energy and supporting nerve cell myelin sheaths.

Hydroxocobalamin

Hydroxocobalamin is a naturally occurring bacterial form that isn't active but converts readily to methylcobalamin and adenosylcobalamin. It's used in injections for deficiencies due to longer storage in the body.

The Inactive, Synthetic B12: Cyanocobalamin

Cyanocobalamin is a synthetic form not found naturally in food. It's used in fortified foods and supplements for its stability and cost. The body converts it to active forms, but this requires an extra step, which may be less efficient for some with genetic mutations like MTHFR.

Natural vs. Synthetic B12: A Comparison


Feature	Methylcobalamin	Adenosylcobalamin	Hydroxocobalamin	Cyanocobalamin
Source	Natural, animal foods & supplements	Natural, animal foods & supplements	Natural, bacterial synthesis	Synthetic, manufactured
Bioavailability	Highly bioavailable; body uses directly	Active form; utilized directly by mitochondria	Converts to active forms; used in injections	Converts to active forms; conversion can be inefficient for some
Primary Function	Supports brain, nerve health, and methylation	Drives mitochondrial energy metabolism	Precursor to active forms; longer retention	Prevents deficiency after conversion
Cost	Generally more expensive	Generally more expensive	Varies by application; cost-effective for injections	Most cost-effective form
Best For	Neurological support; MTHFR mutations	Energy support; cellular metabolism	Sustained B12 levels; severe deficiencies	Cost-effective general supplementation

Sources of Natural B12

Natural B12 comes from bacteria and is primarily in animal products. Rich sources include organ meats, clams, beef, salmon, tuna, dairy, and eggs. Vegetarians, vegans, and older adults may need fortified foods (containing synthetic B12) or supplements to get enough.

Understanding B12 Absorption

B12 absorption is complex. Stomach acid releases B12 from food protein, then it binds to intrinsic factor for absorption in the small intestine. This process can be less efficient with age or certain conditions. High-dose supplements and injections can bypass this via passive diffusion.

Who Should Consider Specific Forms?

Most healthy people can use both methylcobalamin and cyanocobalamin effectively to prevent deficiency. However, those with MTHFR gene mutations, liver/kidney issues, or who prefer naturally occurring compounds may benefit more from active forms like methylcobalamin or adenosylcobalamin.

Conclusion

Natural B12 refers to the active compounds methylcobalamin and adenosylcobalamin, found in animal products and readily used by the body. While synthetic cyanocobalamin is effective for most, understanding the forms helps individuals, especially those with specific health needs, make informed choices. Adequate B12 is crucial for health, nerve function, and energy. For dietary recommendations, consult resources like the NIH Office of Dietary Supplements.

Frequently Asked Questions

Methylcobalamin is a naturally occurring, active form of B12 that the body can use immediately. Cyanocobalamin is a synthetic, inactive form found in supplements and fortified foods, which the body must convert to an active form.

No, natural vitamin B12 is produced by bacteria and primarily found in animal products. Plant-based foods generally do not contain natural B12 unless they are fortified with the synthetic cyanocobalamin.

Research shows varying results on absorption rates. Some studies suggest cyanocobalamin may be absorbed slightly better in small doses, while methylcobalamin may be better retained. For most people, both are effective, but individual genetics and health can influence results.

Most supplements contain either the synthetic cyanocobalamin or one of the natural, active forms, most commonly methylcobalamin. Some high-end supplements may also include adenosylcobalamin.

The best natural food sources of B12 are animal products, including beef liver, clams, fish like salmon and trout, meat, eggs, and dairy products.

Yes, cyanocobalamin is widely considered safe for most people. While it contains a small cyanide molecule, the body can easily detoxify and eliminate this tiny amount.

Some people, particularly those with MTHFR genetic mutations or impaired liver/kidney function, may have difficulty converting synthetic cyanocobalamin efficiently. For these individuals, the pre-converted methylcobalamin can be more effective.