Vitamin B12

Figure 1. The chemical structure of Vitamin B12 (i.e. Cobalamin).

Vitamin B12 or Cobalamin is a micronutrient and one of eight essential B vitamins. Vitamin B12 is a water soluble vitamin and it is required in the human body as a cofactor in DNA synthesis and both fatty acid and amino acid metabolism. Vitamin B12 is important in the normal functioning of the nervous system via its role in the synthesis of myelin, and in the circulatory system in the maturation of red blood cells in the bone marrow.

Vitamin B12 is the most chemically complex of all vitamins. For humans, Vitamin B12 is the only vitamin that must be sourced from animal-derived foods or from supplements. Plants do not contain Vitamin B12, as plants do not require Vitamin B12 to carry out reactions with enzymes. As such, plant-derived foods must be fortified with Vitamin B12 in order to provide it.

In the foods we eat, Vitamin B12 is bound to protein. In the stomach, hydrochloric acid and enzymes unbind Vitamin B12 into its free form. From there, vitamin B12 combines with a protein called intrinsic factor and is absorbed in the small intestine. Supplements and fortified foods already contain B12 in its free form, hence may be more easily absorbed in the body.

Food Sources

Examples of food sources of Vitamin B12 include:

• Fish, shellfish
• Liver
• Red meat
• Eggs
• Poultry
• Dairy products such as milk, cheese, and yogurt
• Fortified nutritional yeast
• Fortified breakfast cereals
• Enriched soy or rice milk

Taken as a Dietary Supplement

As a dietary supplement, Vitamin B12 is used to treat Vitamin B12 deficiency conditions. It is estimated that up to 15% of the general population has a vitamin B12 deficiency, and factors which may contribute to deficiency include inadequate intake of animal derived food products, lack of intrinsic factor (i.e. due to pernicious anaemia, an autoimmune disease), inadequate or supressed stomach acid, and digestive disorders. Symptoms of Vitamin B12 deficiency include:

• Megaloblastic anaemia (a condition of larger than normal sized red blood cells and a smaller than normal amount)
• Pernicious anaemia (a type of megaloblastic anaemia caused by a lack of intrinsic factor so that vitamin B12 is not absorbed)
• Fatigue, weakness
• Nerve damage with numbness, tingling in the hands and legs
• Memory loss, confusion
• Dementia
• Depression
• Seizures

Vitamin B12 is also promoted as a supplement to help reduce the risk of cardiovascular diseases and neurodegenerative diseases (e.g. Alzheimer's, dementia).

The Recommended Dietary Allowance for Vitamin B12 for men and women ages 14+ years is 2.4mcg daily. For pregnancy and lactation, the amount increases to 2.6mcg and 2.8mcg daily, respectively. Being a water soluble vitamin, Vitamin B12 is well tolerated in the human body thus unlikely to cause adverse side effects from high Vitamin B12 intake. No upper limit has been set for Vitamin B12, but some studies have suggested that supplementation of 25mcg per day or higher may increase the risk of bone fractures.