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.
Vitamin B12 and Breastfeeding Recommendations. The Recommended Dietary Intake (RDA) of vitamin B12 for breastfeeding women is 2.8 mcg per day, compared to 2.6 mcg per day for pregnant women and 2.4 mcg per day for most other adults. While the RDA is good for preventing deficiencies in most women, much higher doses are required to treat a deficiency.