If a person does not malabsorb, more than 3 mcg will be absorbed from the usual (not vegan) diet. And if that person has become low because of years of vegan diet, overgrowth of bacteria, or a parasite of another type, the 3mcg per day would help them rebuild stores after the cause of malabsorption has been removed. It would be helpful, but I would prefer to see them rebuild faster with a higher dose.

If a person malabsorbs from food due to too little stomach acid, B12 can still be absorbed just fine from a supplement. That person too could prevent deficiency or rebuild stores with small daily doses of B12 (even 3 mcg). However, that would not be a good idea, because many of those will progress to severe malabsorption, and then they would need much larger doses. [B]So, that is why 1000 mcg is recommended for anyone who has been shown to or might malabsorb. A person who malabsorbs severely may get only about 10 mcg out of 1000 mcg dose.

There are many other scenarios. But, for a person without any symptoms, a regular multi-vitamin containing 3 mcg B12 can be a good insurance policy. If they develop any symptoms or get to be about 50, I would hope they would take a lot more.

Under most circumstances, I think 50 mcg is a pretty silly dose. People who don't malabsorb shouldn't need it, and people who malabsorb severely won't get anything out of it.

rose