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.
How Much B12 Should You Take? The US RDA minimum for Vitamin B12 is 2.4 mcg per day for adults, and 2.8 mcg for pregnant or nursing women. More recent studies put the ideal intake at 4-7 mcg per day.