Vitamin B12 (Cobalamin)
Keywords: nervous system, anaemia, frailty in the elderly
- Detoxifies cyanide (found in tobacco smoke and in some foods)
- DNA synthesis
- Growth and development
- Healthy nerves
Good food sources
Found only in animal foods, although some vegan products are fortified with extra B12 by the manufacturers.
- Disorientation and confusion
- Increased risk of heart disease (by promoting raised homocysteine levels)
- Loss of sensation in feet and legs
- Nerve and spinal cord degeneration (with unsteadiness and mental deterioration)
- Sore, smooth tongue
Low levels of several B vitamins have been found in psychiatric patients and (for B12 in particular) in senile dementia.
Although vitamin B12 is only found in animal foods, vegans (who do not eat any animal foods) survive because our requirements for this vitamin are very small. Yeast extracts used as food flavourings are often fortified with vitamin B12, and vegans should ensure that they consume such foods regularly, or some other product with a guaranteed vitamin B12 content, such as a B12 supplement. Algae and seaweeds are sometimes promoted as plant sources of this vitamin, but they are not a reliable source and some contain only vitamin B12 analogues—substances which are quite similar to vitamin B12 but may actually block the bioavailability of the real vitamin.
Between 16 and 75 per cent of vitamin B12 in a meal is absorbed. The more B12 is ingested, the lower the percentage of absorption. The bioavailability of vitamin B12 is reduced by a lack of intrinsic factor (see below), by parasitic infections and by bacterial overgrowth of the small intestine. Chronic diarrhoea, tapeworm and other intestinal disorders can also inhibit B12 absorption.
Vitamin B12 contains the trace element cobalt, and provides its only known function in the human body.
Pernicious anaemia, which is the vitamin B12 deficiency disease, is not usually caused by a poor intake of this vitamin, but by a lack of ‘intrinsic factor’, a substance found in the stomach which combines with vitamin B12 and allows it to be absorbed by the lower part of the small intestine. Elderly people are particularly susceptible to a lack of intrinsic factor. Without it, only about 1 per cent of dietary vitamin B12 can be absorbed. Intestinal parasites can also cause vitamin B12 malabsorption.
Vitamin B12 deficiency is common even in the presence of normal blood levels, particularly in the elderly. In a study carried out on 548 surviving members of the original Framingham study 12 per cent were found to be B12 deficient. (Lindenbaum J et al. Prevalence of cobalamin deficiency in the Framingham elderly population. Am J Clin Nutr 1994;60(1):2-11.)
Information compiled by Linda Lazarides
Naturopathic Nutritionist, Author, Educator