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.
B12 deficiency is usually detected through a B12 blood level. Typical lower limits of normal are 200 pg/ml. Levels between 150 and 300 should be confirmed with secondary surrogate markers (see following). A CBC test may show macrocytic anemia.12 deficiency is usually detected through a B12 blood level. Typical lower limits of normal are 200 pg/ml. Levels between 150 and 300 should be confirmed with secondary surrogate markers (see following). A CBC test may show macrocytic anemia.