Introduction -- Functions --
-- Required Intakes
protein, iron and
Zinc 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.
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.
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
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
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
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.
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
Reference Nutrient Intakes for Vitamin B12, µg/day. (1000 µg =
0 to 6 months
7 to 12 months
1 to 3 yrs
4 to 6 yrs
7 to 10 yrs
11 to 14 yrs
15 + yrs
Breast feeding women
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.
Vegetarians can rest assured, plant-based foods are loaded with
nutrients including ample protein,
iron and calcium.
Zinc Vitamin B12
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
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
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.
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.
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 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 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
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!