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
There is no published human safety or efficacy data, no reproductive- or developmental-toxicology research, no studies in hepatic or renal impairment, and no drug-interaction studies
When this is the case, one shot wont be nearly enough, because it doesnt last long
While B12 can be stored in your liver for up to five years, you can become deficient (lacking) in it if you don't get enough
For those without an absorption problem, research suggests that high-dose oral B12 supplements can be as effective as injections in raising and maintaining B12 levels