>They seem to be saying "Vegans who don't take supplements or don't eat some esoteric cereal for breakfast every day will become demented."
Esoteric!? Corn Flakes, All-Bran or Raisin Bran are about as far from esoteric as you can get. All three cereals show up near the top of the list of B12 sources in the USDA Nutrient Database PDF linked elsewhere in this thread and all three have been around since my great-grandparent's generation or longer. I'm not sure how long the vitamin fortification has been going on, but it too is very widespread.
Esoteric!? Corn Flakes, All-Bran or Raisin Bran are about as far from esoteric as you can get. All three cereals show up near the top of the list of B12 sources in the USDA Nutrient Database PDF linked elsewhere in this thread and all three have been around since my great-grandparent's generation or longer. I'm not sure how long the vitamin fortification has been going on, but it too is very widespread.