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
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 homocysteineHow 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. 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.
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 soya milk.
In the past, spurious claims have been made that certain fermented soya foods such as miso, tamari and tempeh are rich in vitamin B12; the B12 content of these foods may vary widely and cannot be depended on as a reliable source. Furthermore there have been claims that the algae spirulina and the seaweed nori contain significant amounts of B12. However, the current consensus now is that they contain compounds structurally similar to B12, known as B12 analogues which may disrupt normal B12 metabolism by competing with B12 for absorption. It is wise to assume that no plant foods can be relied on as an adequate source of vitamin B12. While vegetarians may obtain some of their B12 from free-range eggs and dairy products, vegans must obtain their B12 from fortified foods. To ensure that you get enough vitamin B12 become a label reader! If the food is fortified then B12 will be listed in the list of ingredients (how much is present will be given in the nutritional information). Check the nutritional information on the label of fortified foods to ensure that you are getting sufficient B12; it is quite easy to attain the target of three micrograms of B12 per day using fortified foods. Frequent use of fortified foods will ensure an adequate intake for most healthy people.
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.The ability to absorb B12 is important but it is not the only factor that determines B12 status. The bioavailability of the B12 in the diet is just as important as including B12 in the diet; it is pointless consuming lots of B12-rich food if it occurs in a form that the body cannot absorb. The bioavailability of B12 from different food sources has been shown to differ. It has been shown that B12 in fortified foods (such as breakfast cereals) is easier to absorb than the B12 in meat, poultry and fish sources; this seems to apply particularly to the elderly. Indeed, the National Academy of Sciences in the US advise that adults aged 50 and over obtain most of their B12 from supplements of fortified foods, this raises the question that maybe younger adults should consider using these sources as well (7).
