The reason to show it long-hand rather than just stating the answer is that on the 10 mg vial the draw is tiny, and a reader who understands the chain can catch an error the moment a number looks wrong
Tiredness, stress, ill-health, poor or limited diet will all reduce this absorption further. For some people, taking a vitamin B12 supplement is one of the easiest ways to maintain healthy levels
Human clinical trial data remain sparse but are accumulating
the only cross-drug data are weak indirect network meta-analyses
In contrast, there is some evidence of an enhancement of the maximum absorption via intrinsic factor, by up to a factor of 2, when the vitamin B12 is accompanied by food, but this is not consistently observed and probably only applies when the food quantity and vitamin B12 dose are sufficient to slow the passage of the vitamin B12 through the small intestine enough (about three hours or more) to allow each intrinsic factor receptor to absorb two molecules of vitamin B12 from the oral dose rather than one