Vitamin B12 is an important nutrient.
A vitamin is an organic compound and a vital nutrient that an organism requires in limited amounts . Vitamin B12 . It is one of eight B vitamins . B12 is the largest and most structurally complicated vitamin and can be produced industrially only through bacterial fermentation synthesis , typically used to manufacture B12 for fortified foods and supplements . Due to impairment of vitamin B12 absorption during aging , people over age 60 are at risk of deficiency .