Exploring the Spectrum: Understanding the Different Types of Vitamin B12

Welcome to our deep dive into the world of Vitamin B12! In this blog, we'll explore the various types of Vitamin B12 and how each is absorbed by the body. Understanding these differences is crucial for optimizing your health, as each form of B12 serves unique functions and has specific pathways of absorption. Whether you're dealing with dietary restrictions, absorption issues, or just looking to enhance your overall well-being, this guide will provide valuable insights into choosing the right form of B12 for your needs. Let's unlock the potential of this essential nutrient together!



Cyanocobalamin is a synthetic form of vitamin B12 that is commonly used in supplements and fortified foods. It's not directly active in human physiology until converted into the metabolically active forms of vitamin B12: Methylcobalamin or adenosylcobalamin. Understanding how cyanocobalamin is absorbed and utilized in the body requires a closer look at the digestive and metabolic processes involved.

Absorption Process

  1. Ingestion: Cyanocobalamin enters the body through food or oral supplements.
  2. Stomach Activity: When you ingest cyanocobalamin, the acidic environment of the stomach helps release the vitamin from the protein it is bound to in food. People using acid-reducing medications or those with reduced stomach acidity may have difficulties at this stage, affecting the release and subsequent absorption of cyanocobalamin.
  3. Binding with Intrinsic Factor: Once freed from its protein bindings, cyanocobalamin moves to the small intestine, where it must bind with a glycoprotein called intrinsic factor (IF). This binding is crucial as intrinsic factor protects the vitamin from being degraded by the gut environment and facilitates its transportation to the ileum (the last part of the small intestine) where absorption mainly occurs. In conditions like pernicious anemia, the body fails to produce adequate intrinsic factor, severely impacting the absorption of cyanocobalamin.
  4. Absorption in the Ileum: The cyanocobalamin-intrinsic factor complex reaches the ileum, where it binds to specific receptors on the intestinal cells and is absorbed into the bloodstream. Any issues affecting the ileum, such as inflammation from Crohn's disease or surgical removal of part of the intestine, can disrupt this process.

Conversion to Active Forms

Once absorbed, cyanocobalamin must be converted to its active forms — Methylcobalamin and adenosylcobalamin — in the body. This conversion process involves several enzymatic steps and occurs primarily in the liver. Each form of B12 then plays different roles in the body:

  • Methylcobalamin: Vital for functions involving methylation, such as the synthesis of DNA and neurotransmitters.
  • Adenosylcobalamin: Necessary for the metabolism of certain fatty acids and amino acids.

Challenges with Cyanocobalamin Absorption

While cyanocobalamin is a stable and cost-effective form of vitamin B12, its use can present challenges, particularly for individuals with specific health conditions:

  • People with Pernicious Anemia: Due to a lack of intrinsic factor, absorption of cyanocobalamin from the diet is severely compromised.
  • Gastrointestinal Disorders: Conditions that affect the stomach, pancreas, or ileum can impair the digestion or absorption of cyanocobalamin.
  • Genetic Differences: Some individuals may have genetic variations that affect their ability to convert cyanocobalamin to its active forms efficiently.

For these reasons, some health practitioners recommend using supplements that contain Methylcobalamin, hydroxycobalamin or adenosylcobalamin, as these forms do not require conversion and may be better utilized by the body, especially in those with absorption or conversion issues.

While cyanocobalamin is a widely used form of vitamin B12, its effectiveness can be limited by issues related to its absorption and conversion, necessitating consideration of individual health conditions and potentially alternative forms of the vitamin.

Methylcobalamin and hydroxycobalamin are both naturally occurring forms of vitamin B12 and each has distinct features regarding absorption and use in the body. Unlike cyanocobalamin, which is synthetic and requires conversion, these forms of B12 are more directly utilized by the body. Here's how each is absorbed and functions:


Methylcobalamin is one of the two active forms of vitamin B12 found in the human body. It is crucial for processes involving methylation, a biochemical process essential for the proper function of almost all of the body’s systems. It is particularly important for the brain and nervous system health and for the synthesis of molecules involved in the production of energy and DNA.

Absorption and Use:

  1. Ingestion: Methylcobalamin can be obtained through diet or supplements and is found in substantial amounts in animal products such as meat, eggs, and dairy.
  2. Stomach Processing: Similar to other forms, Methylcobalamin is released from food proteins through the action of stomach acid and enzymes.
  3. Binding with Intrinsic Factor (IF): In the stomach, Methylcobalamin binds with intrinsic factor, a glycoprotein necessary for its absorption, which protects it as it travels to the ileum (the latter part of the small intestine).
  4. Absorption: In the ileum, the Methylcobalamin-intrinsic factor complex binds to specific receptors on the surface of cells, facilitating its absorption into the bloodstream.
  5. Utilization: Once absorbed, Methylcobalamin is readily available for cellular uptake and use in its primary role in methylation processes.


Hydroxycobalamin is another natural form of vitamin B12, which is produced by bacteria and used as an injectable form of B12 therapy, especially in cases of B12 deficiency and is also available in table/spray form.

Absorption and Use:

  1. Ingestion or Injection: Hydroxycobalamin is available in both tablet form/spray and as an injectable solution. When administered via injection, it bypasses the gastrointestinal tract entirely, which is particularly beneficial for individuals with absorption issues, ensuring immediate availability and effectiveness. Alternatively, when taken in tablet form, hydroxycobalamin follows the standard digestive and absorption processes, but may not be as immediately bioavailable, especially in those with gastrointestinal impairments.
  2. Direct Entry into Bloodstream: When administered by injection, hydroxycobalamin is directly absorbed into the bloodstream, avoiding the need for intrinsic factor and the potential complications related to the gastrointestinal absorption process.
  3. Conversion and Storage: Once in the bloodstream, hydroxycobalamin is converted into either methylcobalamin or adenosylcobalamin, the active forms of vitamin B12 in the body. It is also known for its higher affinity to plasma proteins, which allows it to stay in the body longer, providing a longer-lasting supply of B12.
  4. Detoxification: Besides its role in B12 metabolism, hydroxycobalamin is used medically to bind with cyanide ions and help detoxify the body in cases of cyanide poisoning.



Adenosylcobalamin, also known as dibencozide, is one of the active forms of vitamin B12 naturally present in the human body. Like methylcobalamin, it plays a crucial role in cellular metabolism, particularly in the conversion of food into energy. Adenosylcobalamin is primarily involved in the metabolism of fats and amino acids and is essential for the formation of myelin, the protective sheath around nerves.

Characteristics and Challenges:

Adenosylcobalamin, although vital, is less stable compared to other forms of vitamin B12 such as cyanocobalamin, Methylcobalamin or hydroxycobalamin. Its instability is particularly evident when exposed to light and certain environmental conditions, where it can degrade more quickly. This sensitivity poses significant challenges for its storage and transport, especially in environments not equipped to handle sensitive substances.

Availability in Australia:

In Australia, the availability of adenosylcobalamin is limited due to these stability issues. Its sensitivity to light and temperature means it does not maintain its potency for long once exposed to environmental conditions typical during shipping and handling. This instability makes it less feasible for manufacturers to produce and distribute adenosylcobalamin as a standalone supplement in regions like Australia.

How it Works in the Body:

  1. Absorption: Like other forms of vitamin B12, adenosylcobalamin is ingested through dietary sources or supplements. It binds with intrinsic factor in the stomach and is absorbed in the ileum.
  2. Utilization: Once absorbed, adenosylcobalamin directly participates in the energy production pathways within cells. It is critical for the conversion of molecules like methylmalonyl-CoA to succinyl-CoA, an important step in the Krebs cycle, which is vital for energy production.

Alternative Sources and Supplements:

Given the difficulty in obtaining stable, effective adenosylcobalamin supplements in Australia, individuals may rely on alternative forms of vitamin B12, such as methylcobalamin or hydroxycobalamin, which are more stable and readily available. These forms can also be converted into adenosylcobalamin within the body, ensuring that the physiological functions dependent on adenosylcobalamin are supported.

For individuals concerned about maintaining adequate B12 levels—particularly vegetarians, vegans, and those with absorption issues— As a specialist in this area, I can provide you with personalized guidance and effective solutions for managing your vitamin B12 levels. I encourage you to book a consultation with me today. Together, we can ensure that your body receives the optimal levels of this essential nutrient for your overall health and well-being.  Additionally, explore our blog on the implications of low B12 levels to understand more about this crucial nutrient.

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