Here’s a collection of average intakes and RDAs for vitamin B12. If you know of any more, please comment and I’ll update this:
The intakes don’t represent daily doses, especially for people like the Okinawans who didn’t eat animal food every day. They’re just averages.
It’s clear that we don’t need very much vitamin B12 … mcg stands for microgram which is 1/1000th of a milligram, and a milligram is 1/1000th of a gram. But we do need some.
I’ve found a good way to get enough but not too much is by using drops.* One drop contains about 40 mcg, a relatively small amount but difficult to find in high-dose pills.
* Liquid vitamin B12, methylcobalamin, serving size: 1 ml (25 drops) provides 1000 mcg B12. This is a 2 fluid ounce bottle I bought for about $8.