10 Things You Need to Know About B12

3. Absorption is Limited

Vitamin B12, bound to protein in food, is released by the activity of hydrochloric acid and gastric protease in the stomach. A healthy body can absorb about 50 to 60% of the vitamin B12 it consumes, because the capacity of intrinsic factor, a gastric glycoprotein that aids in B12 absorption, is limited. When oral doses of B12 exceed one or two mcg at a time, the body's ability to absorb the nutrient decreases. Therefore, experts recommend obtaining multiple small doses through food, or a larger supplemental dose, to maintain optimal B12 levels.