It was Christmas week 1990 in Oakland. Steven Bloom was wandering through The Lot, that timeless gathering of hippies that springs up in the parking lot before every Grateful Dead concert, when a Deadhead handed him a yellow flyer.
Because of the general safety of the vitamin, upper limits for normal intake do not exist. If your blood values for the vitamin fall below a range of 170 to 250 picograms per milliliter, you may develop a B12 deficiency.
According to the U.S. National Library of Medicine, the normal serum vitamin B12 level falls in a range of 200 to 900 picograms per milliliter.itamin B12 is naturally found in eggs, meats, poultry, seafood and milk products. Some foods, like cereal and bread products, are fortified with the vitamin. Although having a high serum level of vitamin B12 could indicate an underlying medical problem, the high level itself isn't detrimental.