Vitamin B12 is important for the normal functioning of the brain and nervous system and for the formation of red blood cells. It is required for the formation of fatty acids in myelin, which is the coating around our nerves. It is also required, together with folate, to produce DNA. It is involved in the metabolism of every cell of the body and vital for fertility.
What happens if Vitamin B12 levels are low?
B12 deficiency can cause a form of anaemia called megaloblastic anaemia. This is where the cells are large and abnormal and not able to carry oxygen around the body adequately. Symptoms include pale skin, lethargy, shortness of breath, palpitations and weight loss.
Nerve cell damage.
Severe B12 deficiency causes damage to nerve cells, can affect the spinal cord and sometimes causes paralysis.
When Vitamin B12 levels in the blood are low, the levels of an amino acid called homocysteine will increase. High homocysteine levels have been identified as a risk factor for heart disease. Homocysteine levels may also be high when folate intake is low. See information on folate.
Vitamin B12 is one of the essential nutrients required for the production of DNA. Damage to DNA can occur when levels of Vitamin B12 are low. DNA damage can affect the way the body functions and can increase the risk of Alzheimer's Disease and even cancer.
What causes Vitamin B12 deficiency?
Poor Vitamin B12 intake
Vitamin B12 is found in abundant amounts in animal foods. It is not present in plant foods. Individuals who eat no animal foods at all (vegans) are at risk of Vitamin B12 deficiency. Vitamin B12 is stored in the body and it can take many years for levels in the blood to drop.
Low levels of intrinsic factor
Intrinsic factor is a glycoprotein produced by the stomach and is necessary for the absorption of vitamin B12. The vitamin is then absorbed into the body in the last part of the small bowel. Levels of intrinsic factor decrease with age and will be severely reduced if part of the stomach is removed during surgery. Lack of intrinsic factor causes pernicious anaemia, which has similar effects to the megaloblastic anaemia described above.
Low stomach acid
The proper activation of B12 by intrinsic factor also requires the acid environment in the stomach. If an individual is taking antacids or if stomach acid is low, then the vitamin may not be activated properly, leading to low levels of Vitamin B12 in the blood.
Activated B12 is absorbed into the blood stream from the last part of the small bowel. If bowel diseases such as Crohn's disease is present, or if the last part of the small bowel has been removed by surgery, then the vitamin may not be absorbed.
Some medications may affect the activation or absorption of Vitamin B12. Discuss this with your doctor or pharmacist.
Where is Vitamin B12 found?
Vitamin B12 cannot be made by plants or animals. The only type of organisms that have the enzymes required for the synthesis of B12 are bacteria. Vitamin B12 is naturally found in foods that harbor B12 bacteria such as meat, particularly liver and shellfish, as well as milk products and eggs. Vitamin B12 is not found in any plant foods. We obtain approximately 25% of our Vitamin B12 from red meat and 30% from dairy foods. Foods such as mushrooms and fermented soy products may have traces of B12 from residual contamination from bacteria, but this is not sufficient to meet requirements and a vegetarian who takes no animal foods (vegan) will require a B12 supplement. A supplement is particularly important for a vegetarian woman who is pregnant or lactating to ensure that the developing infant receives sufficient of the vitamin to prevent irreversible nerve damage.
How much Vitamin B 12 is needed?
The usual recommended intake of B12 for adults is 2.8ug per day. Optimal intake recommended when DNA
damage has been identified is at least 7ug per day. Most individuals will need a supplement in order to achieve this higher intake, and your doctor or dietitian will recommend an appropriate supplement if necessary. No toxic effects of high intakes of B12 have been identified.
Sometimes oral intake of Vitamin B12 will not be effective at increasing levels in the blood, for example, after a total gastrectomy (removal of the stomach) or if the last part of the small bowel has been removed. In this instance regular injections of B12 will be required.
What is the B12 content of certain foods?
Note: All figures are approximate and sourced from US data on the B12 content of food
Vitamin B12 activates another vitamin called folate to help to make healthy red blood cells. Some of the symptoms of low Vitamin B12 levels are therefore closely linked to the symptoms of folate deficiency. Folic acid, particularly in large doses, can mask vitamin B12 deficiency. In vitamin B12 deficiency, folic acid can improve megaloblastic anemia, but potentially irreversible nerve system damage can continue to occur. In this case, Vitamin B12 levels should be checked before folic acid is given by itself.