Vitamin B12 is a common term for a group of chemically related substances that all have vitamin activity. They are also known as cobalamins. The biosynthesis of the basic structure is handled by bacteria that are found many places in nature. The uptake of vitamin B12 from food requires the presence of the protein intrinsic factor that is formed in the gastric mucosa. Intrinsic factor binds to vitamin B12 and transports it into the body from the small intestine. Coli bacteria in the colon also produce vitamin B12 that is taken up by the body. Vitamin B12 is stored in the liver for up to several months at a time, and we humans are also able to reuse vitamin B12 that has been absorbed from the intestine. It is generally more difficult for the body to absorb vitamin B12 compared with other vitamins, and our ability to take up the nutrient decreases as we grow older. The synthetic basic form of vitamin B12 is used in nutritional supplements and also as a food additive. The dosages are typically rather large in order to ensure sufficient uptake of the nutrient.
Functions and importance for
- Formation of red blood cells that carry oxygen to all parts of the body
- Energy levels
- Nervous system - maintenance and new formation
- Mental balance
- Immune system
- Conversion of the amino acid homocysteine to methionine
- Cell division
Deficiencies and poor utilisation may be caused by
- Poor production of intrinsic factor (which is necessary for vitamin B12 uptake)
- Overconsumption of alcohol
- Reduced ability to store the vitamin in the liver
- Old age (especially in combination with an unbalanced diet)
- Estrogen and contraceptive pills
- Sleeping medication
- Doing without animal food sources for long periods of time. Vegans and vegetarians are particularly exposed
- Too little gastric juice and poor intestinal flora
- Fish tapeworm (tapeworms from freshwater fish that consumes large amounts of vitamin B12)
- Chronic pancreatitis (inflammation of the pancreas)
- Long-term use of medical drugs like:
Salicylic acid preparations against intestinal inflammation (Asacol, Pentasa etc.)
Cholesterol-lowering drugs (cholestyramine and clofibrate)
Isoniazid against tuberculosis
Methotrexate against rheumatism and cancer
It normally takes quite a long time for deficiencies to develop, as we humans are able to reuse vitamin B12 and store it in the body for relatively long periods of time. Deficiencies may either occur as minor or major deficiencies. In some individuals, the first symptoms show in the nervous system, while other people show signs of anemia.
- Symptoms of anemia - occur because the cells of the brain, the heart, and the muscles etc. lack blood and oxygen. Symptoms include fatigue, heart palpitations, breathing difficulty, dizziness, and in severe cases headaches, heart cramps, and leg pain (intermittent claudication)
- Megaloblastic anemia that is also seen with folic acid deficiency.
In addition, the following symptoms may occur:
- Red and irritated tongue
- Impaired sense of taste
- Symptoms related to the nervous system
- Impaired memory, mental drowsiness, and dementia
- Numbness of the hands and feet due to nerve damage
- Lack of coordination with cerebral palsy
Children of mothers who consume an unbalanced or vegetarian/vegan diet are at risk of developing vitamin B12 deficiency, which may lead to reduced growth, anemia and in worst case mental retardation.
Vitamin B12 deficiency is often seen in conjunction with lack of folic acid.
Blood samples and diagnosis
Vitamin B12 deficiency is detectable by means of a blood test.
Mainly animal sources such as liver, meat, fish, eggs, and dairy products
Vitamin B12 content in micrograms per 100 grams
|Beef liver/pork liver||111/40|
Recommended daily allowance (RDA)
Adults: 11 years of age and older: 2.5 micrograms
Children: 1-10 years of age: 1 microgram
Pregnancy: Vegetarians and vegans should always take vitamin B12 supplements.
- The above listed deficiency diseases and with use of medical drugs
- Overconsumption of alcohol
- Old age, especially in combination with an unbalanced diet
- Extended periods without animal foods. Special caution should be taken by vegans and vegetarians.
- Use of contractive pills
- In case of pernicious anemia injections should be administered.
Supplements should normally be taken with other B vitamins and not together with antacids.
Overdosing - side effects
No side effects have been observed, not even with large doses. Injections of the vitamin directly into the bloodstream may cause an allergic reaction.