Cyanocobalamin is a synthetic form of Vitamin B12, also known as cobalamin, that is widely used in dietary supplements and to fortify various foods. This compound is a common choice for manufacturers because it offers exceptional shelf stability and is highly cost-effective to produce. When people discover the name contains “cyano,” they often become concerned about the presence of a cyanide group within the molecule. This concern is understandable, but the amount of cyanide is trace and the molecule’s structure renders it non-toxic in this form.
The Chemical Structure of Cyanocobalamin
The core of the Vitamin B12 molecule is a complex structure called the corrin ring, which surrounds a single central cobalt atom. This cobalt atom is the unique feature of all cobalamins, as it forms a coordination bond with a specific chemical group. In cyanocobalamin, the ligand attached to the cobalt atom is the cyanide ion, which is the source of the “cyano” prefix.
This cyanide group is tightly bound to the cobalt atom, forming a highly stable compound. The strong bond prevents the molecule from easily degrading when exposed to light, heat, or oxygen during the manufacturing and storage process. The inclusion of the cyanide ligand essentially acts as a chemical cap that preserves the rest of the large B12 structure. This structural stability is the main reason cyanocobalamin is the most common form found in pharmaceutical preparations and multivitamins.
Calculating the Trace Cyanide Release
The question of how much cyanide is present can be answered precisely by looking at the molecule’s chemical composition. The complete cyanocobalamin molecule has a molar mass of approximately 1355.4 grams per mole, while the cyanide ion that is attached has a molar mass of about 26.02 grams per mole. This means the cyanide ion accounts for approximately 1.92% of the overall mass of the cyanocobalamin molecule.
During metabolism, the body must first cleave the cyanide group from the molecule before the cobalamin can be converted into its active forms. This process, called decyanation, is performed by specific enzymes within the cell, such as the MMACHC protein. If a person takes a typical high-dose supplement containing 1,000 micrograms (\(\mu\)g) of cyanocobalamin, the body will release approximately 19.2 \(\mu\)g of cyanide.
Metabolism and Safety Thresholds
The trace amount of cyanide released during the metabolism of cyanocobalamin is efficiently and safely handled by the body’s natural detoxification systems. The primary mechanism involves the enzyme rhodanese, which is found predominantly in the liver and kidneys. Rhodanese acts as a sulfur transferase, converting the free cyanide into a compound called thiocyanate. Thiocyanate is harmless and is then readily excreted from the body via the urine.
The body’s capacity to detoxify cyanide is so robust that the 19.2 \(\mu\)g released from a standard supplement is negligible compared to amounts encountered in daily life. For instance, consuming a single raw almond can introduce approximately 25 \(\mu\)g of cyanide into the body, a slightly higher amount than the typical B12 dose. Furthermore, chronic exposure to cigarette smoke or eating certain plant foods like cassava exposes individuals to far greater amounts of cyanide.
The safety of this compound is further underscored by its use as a cyanide antidote. A different form of B12, hydroxocobalamin, is administered intravenously to treat cyanide poisoning because its cobalt atom has a high affinity for free cyanide. The hydroxocobalamin binds the toxic cyanide, forming the harmless, stable cyanocobalamin molecule, which is then safely excreted in the urine. Regulatory bodies recognize that the trace amounts from supplements pose no risk to general health, as they are well below established Acceptable Daily Intake levels.
Comparing B12 Forms
The existence of the cyanide group has led to other forms of B12 being promoted as alternatives, primarily methylcobalamin and adenosylcobalamin. Methylcobalamin, which is one of the two active forms of B12 found naturally in the body, features a methyl group instead of a cyanide group attached to the cobalt. Adenosylcobalamin is the other active form, using an adenosyl group instead.
Because methylcobalamin and adenosylcobalamin are the forms the body ultimately needs, some argue they are superior to the synthetic cyanocobalamin. However, for the vast majority of people, the body effectively converts cyanocobalamin into the active methylcobalamin and adenosylcobalamin forms. Both the synthetic and natural forms are considered effective sources of B12 for treating and preventing deficiency. The minute difference in cyanide content between the forms is not a safety concern for a healthy individual.