Does the Cyanocobalamin form of vitamin B-12 have toxic levels of cyanide?

All plants produce cyanide as a by-product of ethylene synthesis. Some plants naturally contain small amounts of cyanide compounds, including stone fruits (almonds, apples, cherries, peaches, and apricots) as well as lima beans, flax seeds, barley, sorghum, white clover, cassava (tapioca), and bamboo shoots.

The amount of cyanide (2% of the weight, or 20 micrograms cyanide in a 1 mg cyanocobalamin tab) is far less than ingested in many natural foods. Following absorption, vitamin B-12 from whatever source is transformed to either methylcobalamin or 5’-deoxyadenosylcobalamin (dibencoszide). Dibencozide is the predominant form of vitamin B-12 in human tissues (up to 70%).

The human body can detoxify a small amount of cyanide in the liver through the thiosulfate (sulfation) pathway. Poisoning occurs when there is not enough thiosulfate to neutralize all the cyanide present. When you’re talking about a dangerous dose of cyanide, it generally means between 50 and 200 milligrams of hydrogen cyanide… but a 1000 microgram (1 mg) pill of the vitamin B-12 supplement cyanocobalamin contains only 20 micrograms of cyanide, and according to dietitian Jack Norris, “the amount of cyanide in cyanocobalamin is considered to be physiologically insignificant.” That’s 20 micrograms, versus milligrams. There are 1000 micrograms in a milligram, which puts the amount of cyanide in a typical B12 supplement far below toxic levels. http://eatdrinkbetter.com/2012/02/22/cyanide/

Neither the U.S. National Institutes of Health’s Institute of Medicine (IOM) nor the European Food Safety Agency (EFSA) have set a Tolerable Upper Intake (UL) level of Vitamin B-12 since each agency has concluded that it is not possible to derive an Upper Level because no clearly defined adverse effect could be identified from medical reports.

• The IOM reported, “The IOM did not establish a UL for vitamin B-12 because of its low potential for toxicity. In Dietary Reference Intakes: Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline, the IOM states that "no adverse effects have been associated with excess vitamin B-12 intake from food and supplements in healthy individuals". Findings from intervention trials support these conclusions.”
• The EFSA reported, “There are also no adverse effects known for vitamin B12 from foods, or from supplements in amounts far in excess of needs.”

Therefore, cyanocobalamin, the predominate form of supplemental vitamin B-12, has been deemed non-toxic even at high levels of intake and the presence of small amounts of cyanide is not unusual in foods.

Sources:
• Centers for Disease Control and Prevention
• Canadian Food Inspection Agency
• Phys.org
• NIH IOM http://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
• EFSA http://www.slv.se/upload/dokument/efsa/upper_level_opinions_full-part33,0.pdf