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.
Normal value ranges for vitamin B12 vary slightly among different laboratories and can range anywhere between 200 to 900 pg/mL. The general consensus is values less than 200 pg/mL constitute a B12 deficiency.ormal value ranges for vitamin B12 vary slightly among different laboratories and can range anywhere between 200 to 900 pg/mL. The general consensus is values less than 200 pg/mL constitute a B12 deficiency.