                             VegSocUK Information Sheet
                             THE VEGETARIAN SOCIETY


   ___________________________________

                                  VITAMIN B12

   Vitamin B12 is a member of the vitamin B complex. It contains cobalt, and so
   is also known as cobalamin. It is exclusively synthesised by bacteria and is
   found primarily in meat, eggs and dairy products. There has been considerable
   research into proposed plant sources of vitamin B12. Fermented soya products,
   seaweeds, and algae such as spirulina have all been suggested as containing
   significant B12. However, the present consensus is that any B12 present in
   plant foods is likely to be unavailable to humans and so these foods should
   not be relied upon as safe sources. Many vegan foods are supplemented with
   B12. Vitamin B12 is necessary for  the synthesis of red blood cells, the
   maintenance of the nervous system, and growth and development in children.
   Deficiency can cause anaemia. Vitamin B12 neuropathy, involving the
   degeneration of nerve fibres and irreversible neurological damage, can also
   occur.

  FUNCTIONS

   Vitamin B12's primary functions are in the formation of red blood cells and
   the maintenence of a healthy nervous system. B12 is necessary for the rapid
   synthesis of DNA during cell division. This is especially important in
   tissues where cells are dividing rapidly, particularly the bone marrow
   tissues responsible for red blood cell formation. If B12 deficiency occurs,
   DNA production is disrupted and abnormal cells called megaloblasts occur.
   This results in anaemia. Symptoms include excessive tiredness,
   breathlessness, listlessness, pallor, and poor resistance to infection. Other
   symptoms can include a smooth, sore tongue and menstrual disorders. Anaemia
   may also be due to folic acid deficiency, folic acid also being necessary for
   DNA synthesis.

   B12 is also important in maintaining the nervous system. Nerves are
   surrounded by an insulating fatty sheath comprised of a complex protein
   called myelin. B12 plays a vital role in the metabolism of fatty acids
   essential for the maintainence of myelin. Prolonged B12 deficiency can lead
   to nerve degeneration and irreversible neurological damage.

   When deficiency occurs, it is more commonly linked to a failure to
   effectively absorb B12 from the intestine rather than a dietary deficiency.
   Absorption of B12 requires the secretion from the cells lining the stomach of
   a glycoprotein, known as intrinsic factor. The B12-intrinsic factor complex
   is then absorbed in the ileum (part of the small intestine) in the presence
   of calcium. Certain people are unable to produce intrinsic factor and the
   subsequent pernicious anaemia is treated with injections of B12.

   Vitamin B12 can be stored in small amounts by the body. Total body store is
   2-5 mg in adults. Around 80% of this is stored in the liver.

   Vitamin B12 is excreted in the bile and is effectively reabsorbed. This is
   known as enterohepatic circulation. The amount of B12 excreted in the bile
   can vary from 1 to 10 micrograms a day. People on diets low in B12, including vegans
   and some vegetarians, may be obtaining more B12 from reabsorption than from
   dietary sources. Reabsorption is the reason it can take over 20 years for
   deficiency disease to develop in people changing to diets absent in B12. In
   comparison, if B12 deficiency is due to a failure in absorption it can take
   only 3 years for deficiency disease to occur.

  DIETARY SOURCES

   The only reliable unfortified sources of vitamin B12 are meat, dairy products
   and eggs. There has been considerable research into possible plant food
   sources of B12. Fermented soya products, seaweeds and algae have all been
   proposed as possible sources of B12. However, analysis of fermented soya
   products, including tempeh, miso, shoyu and tamari, found no significant B12.

   Spirulina, a algae available as a dietary supplement in tablet form, and
   nori, a seaweed, have both appeared to contain significant amounts of B12
   after analysis. However, it is thought that this is due to the presence of
   compounds structurally similar to B12, known as B12 analogues. These cannot
   be utilised to satisfy dietary needs. Assay methods used to detect B12 are
   unable to differentiate between B12 and it's analogues, Analysis of possible
   B12 sources may give false positive results due to the presence of these
   analogues.

   Researchers have suggested that supposed B12 supplements such as spirulina
   may in fact increase the risk of B12 deficiency disease, as the B12 analogues
   can compete with B12 and inhibit metabolism.

   The current nutritional consensus is that no plant foods can be relied on as
   a safe source of vitamin B12.

   Bacteria present in the large intestine are able to synthesise B12. In the
   past, it has been thought that the B12 produced by these colonic bacteria
   could be absorbed and utilised by humans. However, the bacteria produce B12
   too far down the intestine for absorption to occur, B12 not being absorbed
   through the colon lining.

   Human faeces can contain significant B12. A study has shown that a group of
   Iranian vegans obtained adequate B12 from unwashed vegetables which had been
   fertilised with human manure. Faecal contamination of vegetables and other
   plant foods can make a significant contribution to dietary needs,
   particularly in areas where hygiene standards may be low. This may be
   responsible for the lack of aneamia due to B12 deficiency in vegan
   communities in developing countries.

   Good sources of vitamin B12 for vegetarians are dairy products or free-range
   eggs. A half pint of milk (full fat or semi skimmed) contains 1.2 micrograms.
   A slice of vegetarian cheddar cheese (40g) contains 0.5 micrograms. A
   boiled egg contains 0.7 micrograms. Fermentation in the manufacture of
   yoghurt destroys much of the B12 present. Boiling milk can also destroy
   much of the B12.

   Vegans are recommended to ensure their diet includes foods fortified with
   vitamin B12. A range of B12 fortified foods are available. These include
   yeast extracts, Vecon vegetable stock, veggieburger mixes, textured vegetable
   protein, soya milks, vegetable and sunflower margarines, and breakfast
   cereals.

  REQUIRED INTAKES


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VegSocUK Information Sheet
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   The old Recommended Daily Amounts (RDA's) have now been replaced by the term
   Reference Nutrient intake (RNI). The RNI is the amount of nutrient which is
   enough for at least 97% of the population.

   Reference Nutrient Intakes for Vitamin B12, micrograms/day. (1000 micrograms = 1 mg).

Age                     RNI

0  to  6  months        0.3 micrograms
7  to  12 months        0.4 micrograms
1  to  3  yrs           0.5 micrograms
4  to  6  yrs           0.8 micrograms
7  to  10 yrs           1.0 micrograms
11 to  14 yrs           1.2 micrograms
15  +  yrs              1.5 micrograms

Breast feeding women    2.0 micrograms

   Pregnant women are not thought to require any extra B12, though little is
   known about this. Lactating women need extra B12 to ensure an adequate supply
   in breast milk.

   B12 has very low toxicity and high intakes are not thought to be dangerous.
   ___________________________________


//
This article is copyright to the Vegetarian Society (UK), but may be freely
copied for non-commercial use provided it is kept intact, not altered
and these lines are included.

For futher information contact: The Vegetarian Society, Parkdale, Dunham Road,
Altrincham, Cheshire WA14 4QG, England. Tel: (England) 061 928 0793
email: vegsoc@vegsoc.demon.co.uk
//



[The text of this file was obtained from the Vegetarian Society (UK) in
March 1995.]

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