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Vitamin B12

Introduction -- Functions -- Dietary Sources -- Required Intakes

Fact & Info

protein, iron and calcium.

Zinc  Vitamin B12

Vitamin D

Introduction

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 2-5mg 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 10ug (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, an 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. ½ pint of milk (full fat or semi skimmed) contains 1.2 µg. A slice of vegetarian cheddar cheese (40g) contains 0.5 µg. A boiled egg contains 0.7 µg. 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

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, µg/day. (1000 µg = 1mg)

 

Age

RNI

0 to 6 months

0.3 µg

7 to 12 months

0.4 µg

1 to 3 yrs

0.5 µg

4 to 6 yrs

0.8 µg

7 to 10 yrs

1.0 µg

11 to 14 yrs

1.2 µg

15 + yrs

1.5 µg

Breast feeding women

2.0 µg

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.

acknowledgement-online source: http://www.vegsoc.org/info/b12.html

 

 

 

 

 

 

 

 

 

 

 

Key Nutrients
Vegetarians can rest assured, plant-based foods are loaded with nutrients including ample protein, iron and calcium.

Zinc  Vitamin B12

Vitamin D
 
Whether you eat a vegetarian or non-vegetarian diet, the key to health is simple. Include a wide variety of different foods in your diet – no one food source is nutritionally complete by itself. Vegetarians choose foods from grains, vegetables, legumes, nuts, seeds and fruits. Whole unrefined foods are best. Eggs and dairy are optional. On a plant-based diet, you will have the distinct advantage of obtaining nutrients from sources high in fibre, and low in saturated fat and cholesterol.

Protein
It was once thought that foods had to be combined within a single meal to provide complete protein but it is now clear, as stated by the American Dietetic Association, that conscious combining of plant foods at a given meal is not necessary. Most people can easily meet their protein needs by eating a variety of whole grains, legumes, and vegetables on a daily basis. Although there is somewhat less protein in a vegetarian diet, this is actually an advantage, as excess protein has been linked to heart disease, strokes, various cancers, kidney stones and osteoporosis. Foods high in protein include tofu, tempeh, TVP, beans, nuts, seeds, soy milk, eggs, cheese, yoghurt and dairy milk.


Iron
Only about one fifth of the iron in a standard diet comes from meat. Dairy products are deficient in iron. The richest plant sources are dark green vegetables, soy products and legumes, whole grains, dried fruits, nuts and seeds. Cooking with cast-iron pots also contributes to dietary intake. Adding foods high in vitamin C to your meals, such as fruits and greens, enhances iron absorption. Foods that contain factors that decrease absorption include: tea, coffee, milk, cheese, spinach, rhubarb, Swiss chard and chocolate.

Calcium
Dairy products are high in calcium, but needs can also be met on a well planned vegan diet (containing no animal-source foods). Rich plant food sources include dark green vegetables such as broccoli, bok choy and kale, beans, tofu (made with calcium), tahini, sesame seeds, almonds, figs, seaweeds, and fortified soy milks. Since the consumption of animal protein increases calcium requirements, a person following a vegan diet may have much lower needs. Although some plant foods contain oxalates and phytate which can inhibit calcium absorption, the calcium in plant foods is generally well absorbed.

Vitamin D
This vitamin is essential for the absorption of calcium and is formed in the presence of direct or indirect sunlight. Your body stores vitamin D during the summer for winter use. On average, about 10 to 15 minutes a day of sun on the face and hands for light-skinned people should suffice. Darker-skinned people, the elderly, and those at higher latitudes may need more sun exposure. Sunscreen lotion rated SPF 8 or above prevents vitamin D synthesis. Dairy products and some soy milks are fortified with vitamin D. People getting insufficient sun or not eating fortified foods should consider taking a daily multiple vitamin with 400 IU of vitamin D.

Zinc
Zinc is readily available in many plant foods – whole grains (breads, pasta, rice), wheat germ, tofu, tempeh, miso, legumes, sprouts, nuts and seeds – as well as eggs and dairy products.

Vitamin B12
Vitamin B12 is produced by micro-organisms in the soil. In the past, root vegetables contained adequate amounts of B12. Today root vegetables are cleaned so well that all traces of B12 are removed. Meat-eaters acquire B12 through micro-organisms living in the animal flesh they eat. Lacto-ovo vegetarians receive B12 through eggs and dairy products. Obtaining enough B12 through a vegan diet is more challenging. Although cases of B12 deficiency are rare, it can cause pernicious anemia, a serious deficiency disease. Confirmed vegan sources include fortified soy milks, other fortified foods, vitamin pills, and Red Star nutritional yeast (T6635+). Red Star is available at many natural food stores. Other sources which may prove reliable are the surface bacteria on lightly washed organic vegetables, and bacterial activity in the small intestine, but these are not scientifically verified. Long term studies of vegans have detected a very low rate of B12 deficiency. In fact, more meat-eaters than vegans suffer from this deficiency due to problems absorbing B12. The human body stores a 2-7 year supply of vitamin B12. It's especially important for women to ensure B12 intake when pregnant or breastfeeding.

All other vitamins, minerals, fats and carbohydrates are widely found in the plant kingdom. These nutrients can be easily obtained by maintaining variety in a plant food diet. If you have difficulty adapting to a vegetarian diet it may be that your body needs a few months to adjust and detoxify. Try experimenting with a variety of different foods and cooking methods. If you have concerns about a nutrient deficiency, you can always have your blood tested, but rest assured that a varied vegetarian diet lacks no nutrients and is proven to be a powerful health promoting choice. Bon appetit!

 

acknowledgement-online source: http://www.veg.ca/noframes/facts/key.htm