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B12 and the Vegan Diet
All You Need To Know About Vitamin B12 in Vegetarian and Vegan Diets
The association of vitamin B12 with animal foods such as fish, meat, poultry, eggs, milk and dairy products has helped create the myth that this vitamin can only be obtained from these foods and that a vegetarian or vegan diet provides a substandard amount. Consequently B12 has become a contentious issue. Concerns that vegetarians, and especially vegans, are at risk of B12 deficiency prevail even though the evidence suggests the meat-eating elderly are by far the group most likely to be deficient in B12. Furthermore, research suggests that the B12 present in meat, poultry and fish is not as easily absorbed as the B12 present in fortified vegetarian foods.
What are the B Complex Vitamins and Why Do We Need Them?
The B complex vitamins are a group of water-soluble compounds that act as ‘cofactors’ or helpers in different enzyme systems in the body. In other words, they are involved in a wide range of biochemical reactions in the body. Reactions include the synthesis of fatty acids and DNA.
Vitamin B12 is a complex molecule; it’s common name, cobalamin reflects the presence of the mineral cobalt in the centre of its structure. As with the other B vitamins, B12 helps build the material that makes up our genetic blueprint; our DNA. It is also particularly important in the production of red blood cells and in maintaining a healthy nervous system. B12 also helps release energy from our food. A further important role of B12 is to act in conjunction with folic acid (another B vitamin) in the synthesis of the amino acid methionine; this limits the build up of a potentially damaging molecule known as homocysteine (more on this later).
How Much Vitamin B12 Do We Need?
In the UK, the reference nutrient intake value (RNI) is used; this is similar to the Recommended Daily Amount (RDA) used previously. The RNI value for a nutrient is the amount of that nutrient that is sufficient for 97.5 per cent of the people in a given group. The UK government currently suggests that the RNI value for Vitamin B12 in adults aged between 19 and 50 years of age is one-and-a-half micrograms per day (1). The current European Union (EU) recommended daily allowance is even lower at only one microgram per day. These figures are based on preventing B12 deficiency and therefore may not represent the optimum intake. It has been suggested that three micrograms per day from fortified foods (or 10.0 micrograms per day from a supplement if you don’t eat fortified foods) should ensure an adequate intake of B12 and minimise the build up of homocysteine (2). Currently, there isn’t enough evidence to know what the effects of taking high doses of vitamin B12 supplements each day might be.
Food Sources of Vitamin B12
Vitamin B12 is manufactured by microorganisms (bacteria, fungi and algae) - especially bacteria in soil and water, and to some extent bacteria in the gut, although production in the gut occurs in a different area to where absorption takes place. Animals obtain B12 from food and water contaminated with these microorganisms. Plants do not require B12 and therefore have no mechanism to produce, absorb or store it. Therefore humans must obtain B12 in the diet, either from animal sources (red meat, fish, poultry, eggs and dairy products) or from fortified plant-based foods. While plants do not naturally contain B12, they may carry some through microbial contamination. Plant-eating primates such as the gorilla (and our human ancestors and many people in developing countries) obtain a plentiful supply of B12 from their consumption of plants due to the presence of insects and bacterial contamination of their plant foods and water. Some primates eat faeces and soil which may also provide a source of B12. When fed a sanitised diet, in a zoo for example, primates often develop B12 deficiency (2).
In modern society, fruit and vegetable production is far more sanitised in that fruit and vegetables are washed in chlorine for sale in supermarkets. This removes the B12-producing bacteria and so vegetarians and vegans must obtain vitamin B12 from other sources, this means fortified foods. The industrial production of vitamin B12 for the fortification of foods involves fermentation with bacteria. Large-scale production is carried out using a number of bacterial species, including for example Pseudomonas denitrificans, Propionibacterium freudenreichii and Propionibacterium shermanii. Bacterial cultures are grown in huge vats for the extraction of B12.
B12 can be obtained from many everyday food items that are fortified such as veggie burger and sausage mixes, yeast extracts, vegetables stocks, margarines, breakfast cereals and soya milks. See below for guide to how much B12 is contained in a range of these foods.
So, as the table shows, the EU recommended daily amount
of B12 can be obtained for example from one slice of Meridian
yeast extract on toast or one glass of B12 –fortified
Vitamin B12 Absorption
B12 metabolism is complex and requires many processes.
The first stage is consumption of B12-containing food. B12
from meat is bound to animal protein. In order to absorb
this form of B12 gastric secretions are required to remove
the animal protein and release the B12. B12 produced by bacteria
(used in fortified foods) is not bound in this way and so
is easier to absorb. Once the animal protein is removed (or
if it was never present as in fortified foods supplemented
with B12 produced by bacteria), the free B12 binds to other
proteins to form complexes that travel further along the
digestive system. Enzymes break up these complexes to release
the B12 molecule which then binds with an important molecule
called intrinsic factor. B12 can only be absorbed in the
small intestine in the presence of intrinsic factor. The
B12-intrinsic factor complex attaches to cells in the final
section of the small intestine (the ileum) where transport
proteins bind to it and distribute it into cells all around
the body (the liver is the predominant storage site). B12
enters the cells where it is broken down and converted into
biologically useful molecules.
Vitamin B12 Deficiency
B12 deficiency can be divided into four stages. First of all, levels of B12 in the blood drop, then levels of B12 in the cells fall, then a biochemical deficiency occurs whereby levels of B12-related compounds are disrupted and finally clinical deficiency (or megaloblastic anaemia) occurs (3). This condition is characterised by abnormally enlarged immature red blood cells that are unable to divide properly. The abnormal cells are unable to transport oxygen efficiently thus chronic vitamin B12 deficiency can lead to a range of problems from fatigue, tingling and numbness of the limbs (4) to damage to nerve cells (3), the spinal chord (5) and the brain (6). In extreme cases paralysis or death may result from vitamin B12 deficiency.
What Causes B12 Deficiency?
B12 deficiency is rare; the most common cause is malabsorption which results from some condition of the stomach or of the small intestine. This type of deficiency usually requires treatment with B12 injections. This type of deficiency has nothing to do with the amount of B12 present in the diet - it arises from inadequate absorption due to a wide range of physiological or medical conditions. Furthermore, B12 absorption tends to decrease with age (7). For example, in the elderly a decline in the production of acid in the stomach may reduce B12 absorption, although this mainly affects B12 absorption from meat. The most common cause of B12 deficiency in the UK is the loss of intrinsic factor; this may result from a genetic predisposition and tends to be age-related (3).
B12 deficiency can arise if any of the stages of metabolism are not completed. For example B12 malabsorption may occur if surgery has been performed on the digestive system (such as a gastrectomy or ileal resection) or in the case of gastrointestinal disorders such as Crohn's disease (8). In autoimmune diseases the body’s normal responses to molecules perceived as foreign invaders (such as bacteria and viruses) go wrong and the body attacks itself. A condition called pernicious anaemia may result from an autoimmune disease that targets the cells that produce intrinsic factor, this condition is characterised by large immature red blood cells. Pernicious anaemia is most common in older people. It affects about 1 in 8,000 people over the age of 60. It is more common in women than in men and in people with fairer colouring. Symptoms of anaemia include tiredness, shortness of breath and palpitations. In some more serious cases symptoms may include soreness of the tongue, weight loss, paling skin colour, diarrhoea, and poor resistance to infections. In extreme cases there may be a tingling sensation in the fingers and toes, muscle weakness and confusion.
Additional causes include stomach infections with the bacterium Helicobacter pylori (3), the single-celled parasite Giardia lamblia (9) or the parasitic worm Enterobius vermicularis (10). These parasites can interfere with normal B12 absorption by competing with the host organism (that could be you!) for the B12 present in the diet.
The total number of people estimated to have B12 deficiency varies widely; this is largely due to how B12 deficiency is defined. The discrepancy in the figures reflects how B12 deficiency may go undiagnosed as symptoms are subtle and may not be noticed. A recent review reported that B12 deficiency is estimated to occur in anything between five and 60 per cent of the general population of industrialised countries (11). This suggests B12 deficiency is a problem for meat, poultry and fish eaters as much as anyone else. Indeed it may be worse for them as they do not actively seek out fortified foods and the B12 they consume is bound to animal protein. However, in 2004 a UK government survey suggested that only two per cent of men and four per cent of women had a serum vitamin B12 concentration below the limit of the normal range (1). Vitamin B12 deficiency does however occur frequently in the elderly (12), indeed it has been estimated that up to 40 per cent of elderly people suffer B12 malabsorption due to atrophic gastritis; inflammation of the stomach leading to a reduction in acid production (7).
More rarely, B12 deficiency may occur among people whose diets lack any B12. This type of deficiency is very rare but the consequences can be extremely serious especially for infants. Furthermore, when vitamin B12 is absent from the diet, deficiency may take some time to occur as stores in the liver are used up. The authors of a recent review of studies on B12 deficiency agree that nutritional deficiency of B12 is rare among healthy adults in industrialised countries and estimate that deficiency caused by lack of B12 in the diet only accounts for five per cent of all cases seen (13).
Since the early 1990’s the amino acid
homocysteine has become the subject of much interest among
the scientific community. Evidence suggests that homocysteine
damages the lining of blood vessels and enhances blood clotting.
Elevated concentrations of homocysteine in the blood have
been linked to Furthermore, the study acknowledged that the
actual intakes of an increased risk for heart disease and
stroke. Some studies B12 and calcium might now be higher
because the number of suggest it may have an even more important
role in determining foods fortified with B12 has increased
in recent years. It may be the health of individuals than
cholesterol (2). Homocysteine is that vegetarians and vegans
have gained an advantage in that they converted into the
amino acid methionine in the presence of are used to routinely
consuming B12-fortified foods and are B12. In the same reaction,
methyltetrahydrofolate is converted therefore less likely
to experience B12 deficiencies associated with to folate
which is used in the synthesis of DNA. This entire age-related
gastrointestinal conditions. reaction relies on sufficient
supplies of B12, B6 and folate. In B12 deficiency, the amount
of homocysteine in the body can Numerous studies now demonstrate
that any actual deficiencies of escalate to potentially dangerous
levels and has been linked to a B12 in a vegetarian or vegan
diet are usually due to poor meal range of disorders including
depression, dementia, damage to planning (20). While vitamin
B12 may be the nutrient most likely the inner lining of the
artery walls and may be a trigger for to be missing from
a vegetarian or vegan diet, meat remains an
How is B12 Deficiency Diagnosed and Treated?
Vitamin B12 deficiency may be diagnosed by measuring the levels of serum B12 or by measuring the levels of homocysteine; which can accumulate to high levels in the absence of B12. However, high homocysteine levels can also be caused by folate or vitamin B6 deficiencies. Conventionally vitamin B12 deficiency is treated with a course of intramuscular injections. A B12-like compound called hydroxocobalamin is injected into the muscle every two to four days. Around six injections are given to build up stores of vitamin B12 in the liver. Blood tests are given periodically to monitor the success of the treatment (15).
Vegetarians, Vegans and Vitamin B12 Deficiency
Several reports single out vegetarians, and particularly vegans, as a high risk group for vitamin B12 deficiency. (16, 17, 18). One extensive UK study described the nutrient intakes of over 65,000 people including 33,883 meat-eaters, 10,110 fish-eaters, 18,840 lacto-ovo vegetarians and 2,596 vegans (19). This EPIC-Oxford cohort currently includes the largest number of vegetarians than any comparable study in the world. The study concluded that vegans had the highest intakes of fibre, vitamin B1, folate, vitamin C, vitamin E, magnesium and iron, and the lowest intakes of retinol, vitamin B12, vitamin D, calcium and zinc. But this does not necessarily mean they were deficient in any of these nutrients.
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