Vitamin B12

Vitamin B12 (cobalamin) is essential for blood formation, nerve sheaths and methylation. It can only be taken up from animal foods or supplements and requires intrinsic factor from the stomach. Serum B12 is often unreliable – the active holo-transcobalamin (holo-TC) shows the functional status more precisely.

How vitamin B12 acts in the body

Vitamin B12 is released from dietary protein in the stomach with the help of stomach acid, binds to intrinsic factor from the parietal cells of the stomach and is absorbed in the last section of the small intestine. The liver stores reserves for several years. In the cells, B12 works in two enzymes: methionine synthase, together with folate, converts homocysteine into methionine and thereby supplies SAM and methylation; methylmalonyl-CoA mutase processes certain fatty and amino acids and is important for the myelin sheaths of the nerves.

Low vitamin B12 – what happens in the body?

When B12 is lacking, methionine synthase stalls: homocysteine rises, methylation reactions are slowed and folate remains trapped in a form the cell cannot use. Rapidly dividing cells suffer first: blood formation produces fewer but oversized red blood cells (megaloblastic anaemia), and mucous membranes renew less well, for example with a burning tongue. At the same time methylmalonic acid builds up and the myelin sheaths of the nerves are damaged – with tingling, numbness, unsteady gait and memory problems; this nerve damage can also occur without anaemia. Causes are low intake (vegan diet), too little stomach acid or intrinsic factor (for example with autoimmune gastritis, acid blockers or metformin) and diseases of the small intestine.

High vitamin B12 – what does it mean?

A high value usually results from taking vitamin B12; excess is excreted by the kidneys. Without supplementation, high levels can occur with liver and kidney disease or certain blood disorders, because more transport protein is then present in the blood or B12 is released from stores – the treating practice assesses this.

The interpretation is given in your report.