Vitamin B12, also known as cobalamin, has a complex mechanism of action in the body. It is a water-soluble vitamin, which means it’s dissolved in water and transported through our bloodstream. Here’s a breakdown of how the body uses and processes vitamin B12:
Dietary Intake: We consume vitamin B12 primarily from animal products such as meat, poultry, fish, and dairy. Some foods are also fortified with B12.
Stomach Processing: When we eat foods containing B12, the vitamin is bound to protein. In the stomach, hydrochloric acid and gastric protease enzymes release B12 from these proteins.
Binding to Intrinsic Factor: In the stomach, B12 then binds to a protein made by the stomach lining called “intrinsic factor” (IF). This B12-Intrinsic Factor complex is crucial for the absorption of B12 in the small intestine.
Absorption: The B12-Intrinsic Factor complex moves to the ileum, which is the last part of the small intestine. Here, cells have receptors that allow for the uptake of this complex, effectively absorbing B12 into the bloodstream.
Transport in Blood: Once in the bloodstream, B12 binds to proteins called transcobalamins. The primary complex is B12-transcobalamin II, which delivers B12 to body cells.
Cellular Uptake and Utilization: Inside cells, B12 undergoes various transformations to become its two active coenzyme forms: methylcobalamin and 5-deoxyadenosyl cobalamin.
Methylcobalamin: This form is crucial for the conversion of homocysteine to methionine. Methionine is then used to make SAMe (S-adenosylmethionine), which is involved in many methylation reactions, including DNA and neurotransmitter synthesis.
5-Deoxyadenosyl Cobalamin: This form is involved in the conversion of methylmalonyl-CoA to succinyl-CoA, a crucial step in the breakdown of certain fats and proteins for energy.
Excretion: The body excretes excess B12 and its breakdown products via the kidneys in urine.
The body’s ability to use vitamin B12 can be affected by various factors, including genetic mutations