Methylcobalamin vs cyanocobalamin: which form of vitamin B12?

“Cobalamin” is the name for a group of molecules built around a cobalt atom. What differs between them is the small group attached to that cobalt. In the body, two forms do the actual work: methylcobalamin and adenosylcobalamin. Supplements mainly use cyanocobalamin, methylcobalamin, or hydroxocobalamin.

Cyanocobalamin is the form most often used in supplements and fortified foods. It carries a cyanide group, which makes the molecule very stable and inexpensive to produce. The body removes this group and converts the cobalamin into its active forms.

The word “cyanide” sounds alarming, but the amount released from a supplement is tiny — far below anything considered harmful. Cyanocobalamin is also the form used in most of the research on B12 supplementation.

Methylcobalamin is one of the two active forms of B12 and occurs naturally in food. It does not need the conversion step that cyanocobalamin needs. It is less stable to light than cyanocobalamin, which is something manufacturers have to account for.

Both forms raise vitamin B12 levels in the body. Reviews comparing them describe differences in how they are absorbed, retained and excreted, but there isn’t strong evidence that one form gives healthy people a meaningfully different result than the other. Cyanocobalamin has the larger body of research; methylcobalamin has the advantage of already being an active form.

In other words, the choice is reasonable either way. What matters more is getting a reliable, regular intake.

The reference intake for vitamin B12 on EU labels is just 2.5 µg per day. Yet supplements commonly contain 100 µg, 250 µg or more — thousands of percent of the reference intake. There’s a reason for that.

B12 is absorbed in two ways. The main route uses a protein called intrinsic factor, and it can only handle a small amount — about 1.5–2 µg — at a time. On top of that, around 1% of a larger dose is absorbed passively. Higher doses compensate for this limited uptake. EFSA has not set an upper limit for vitamin B12, as no adverse effects have been linked to high intakes.

Vitamin B12 is found almost only in animal foods: meat, fish, eggs and dairy. People who eat a vegan diet need B12 from fortified foods or a supplement — the Swedish Food Agency recommends this. Absorption can also become less efficient with age, and some medications affect B12 uptake. If that applies to you, talk to your doctor.

As with all EU health claims, these apply to vitamin B12 itself, regardless of form.