There are many different Vitamin B12 supplements available, and most of them provide very high levels of B12 – as much as 5000 mcg in some cases. This sounds like a lot when you consider that the recommended daily intake of Vitamin B12 is only about 3 mcg. However, absorption rates for Vitamin B12 depend on the amount consumed, and can range from 50%, if the daily recommended amount of 3 mcg is obtained from food, down to as low as 0.5% if a supplement containing 1000 mcg or more of Vitamin B12 is taken. So the amount of B12 that is actually absorbed from high-dose supplements may be only slightly higher than the amount absorbed from a combination of foods fortified with B12.