There are many more people who don’t have enough B12 than we thought.
Vegans or vegetarians are particularly likely to be B12 deficient, but older individuals or people taking certain oral medications for diabetes (metformin) or acid reflux (PPIs and H2-blockers) are also quite often B12 deficient. B12 is important for correct gene expression, unborn children of pregnant women with B12 deficiency are especially at risk for brain and spine malformations.
B12 deficiency used to be only associated with an autoimmune condition called Pernicious Anemia. This condition is a result of an immune destruction of a protein made in the stomach called Intrinsic Factor (or IF) or the cells that make it.