I'm a strict vegetarian ( but not a vegan) but a little worried
about my vitamin B12 levels. Is it true B12 can only come from an
Dave, Bedford, England
Thanks for your letter about B12.
Yes, you are right, animal sources are the only reliable sources
of B12. But you eat dairy products. They are from animal sources
too, remember! So it seems a lacto vegetarian diet is sufficient.
Last week I got my B12 count checked. It was a little above average,
in other words, acceptable. I have not eaten meat since 1968, so
my vegetarian diet seems to be working. So 36 years without meat
has had no ill effects on my B12.
Here's some information on 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
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 0ug (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, hoyu
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 ith B12 and inhibit metabolism.
The current nutritional consensus is that no plant foods can be
relied on as a safe source of vitamin B12.
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. 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 population.
Reference Nutrient Intakes for Vitamin B12, µg/day. (1000
µg = 1mg)
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 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.
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