Vitamin B12 (Cyanocobalamin)

Description Vitamin B12 is a water soluble vitamin and a member of the B-vitamins group.
Function/ Used for Vitamin B12 is essential in the functioning of the nervous and immune systems; red blood cell formation and RNA and DNA synthesis.

It is also involved in energy production and works synergistically with vitamin B6 and folic acid in homocysteine (an amino acid) metabolism.

It also helps to reduce tiredness and fatigue.

Intake Recommended intake

EU NRV: 2.5µg (micrograms)


UK average daily intake

Requirements vary depending on age and gender. The UK National Diet and Nutrition Survey lists up-to-date intake requirements and average intakes1.

As a supplement Available as a single supplement. Also commonly available as part of a multivitamin and mineral formula.

Different multivitamin and minerals products will vary in the percentage NRVs they include. People should always check the label for information about a specific product.

Found in (dietary sources) Vitamin B12 is found only in animal products and certain foods fortified with the vitamin, therefore, vegans and strict vegetarians are at risk of deficiency. Good sources include meat, liver, kidney, poultry, fish, eggs, dairy products and fortified breakfast cereals.
Deficiency Deficiency of vitamin B12 leads to enlarged, but fewer red blood cells (megaloblastic anaemia).

Other deficiency symptoms include mood changes, sore tongue, fatigue, weakness and lack of concentration.3

Precautions and contraindications None known.

Safe Upper Level: 2000µg/day1

Use in pregnancy and breastfeeding There is no evidence of adverse effects in pregnancy with normal intakes.
Interactions e.g. with other medications Excessive intake of alcohol may reduce the absorption of vitamin B12.

Oral contraceptives may reduce blood levels of vitamin B12.

Large doses of folic acid given continuously may reduce vitamin B12 in blood or may mask symptoms of megaloblastic anaemia.

Vitamin C may destroy vitamin B12 (avoid large doses of vitamin C within one hour of taking oral vitamin B12).3,4


All B vitamins act synergistically and excess levels of one may lead to imbalance or deficiency in others.  It is advisable to take B vitamins as a complex rather than as single substance supplements.

Adverse effects Vitamin B12 may occasionally cause diarrhoea and itching skin. Megadoses may exacerbate acne.
References 1.

2.       Expert Group on Vitamins and Minerals, 2003.

3.       Mason, P. Dietary Supplements. Pharmaceutical Press, London, 2001.

4.       Gaby, A. R. A-Z Guide to Drug-Herb-Vitamin Interactions. HealthNotes 2006.