It isn't. Someone has been producing false claims.

Resin

When I was in graduate school, 1966 or there about, the story the professor told went something like this. Early researchers working with auxins were trying to identify their uses chemically. Early researchers working with vitamins were trying to identify their uses chemically. Someone found B12 in a root growth concoction and thought it to be the active ingredient and tried marketing B12 as a root growth substance. This was once the myth behind the folklore as told a half century ago.

Some seaweeds contain similar molecules that are not active as vitamins.

Right Joanie, but that doesn't stop a zillion vitamin companies from selling them as B12. And it is the most common form of pseudo B12 sold too. What a racket.

Lainey

Everyone, look at this.

Best source is snake oil. Ask any snake oil dealer.

Resin