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by Daphne Lambert

The importance of vitamin B-12 in the diet particularly for people who eat a plant based diet


Natural sources of vitamin B-12 are restricted to foods of animal origin and not generally in plant based foods as they do not require B12 and therefore have no mechanism to produce, absorb or store it. For those who choose to abstain from the use of animal products careful consideration must be given to how optimum B-12 in the diet is achieved.


The role of vitamin B-12

Vitamin B-12 is integral to normal, healthy energy metabolism in all cells of the body, as well as amino acid and fatty acid metabolism.

It works together with folate in the synthesis of DNA and red blood cells.
It is involved in the production of the myelin sheath around the nerves, and the conduction of nerve impulses.
It is necessary for cognitive health.
Vitamin B-12 is involved in the prevention of excessive homocysteine build-up. A long list of cardiovascular diseases have been associated with excessive accumulation of homocysteine in the bloodstream, including coronary heart disease, peripheral vascular disease, and stroke. Vitamin B12 helps normalize levels of homocysteine in the blood by allowing conversion of homocysteine to methionine.


People at risk of vitamin B-12 deficiency

B12 deficiency can occur even in people eating large amounts of B-12 containing animal products, however research shows deficiency is far greater in vegetarians and vegans.

The role of vitamin B-12 in DNA synthesis and red blood cell production is primarily to recycle folate. A high intake of folate, which is often the case for people eating a plant based diet  can  compensate for insufficient folate recycling. Unfortunately, this means that a high-folate diet can forestall the development of anemia, which is easily detectable with a simple blood test, while potentially irreversible nervous system degeneration progresses without warning. Vegetarians & vegans who consume large amounts of folate-rich green leafy vegetables could therefore be at risk for a form of vitamin B12 deficiency that is not considered severe until it is too late.


Older age groups can be deficient in vitamin B-12  this is often caused by the decreased ability of the digestive system to absorb nutrients. This means that even if you optimize your diet to contain high amounts of B12, most of it only passes through the digestive system unabsorbed.


People with intestinal dysbiosis, gut inflammation, hypochlorhydria (low stomach acid) or  those taking certain medications especially PPIs and other acid-suppressing drugs are at risk as are those who consume a lot of alcohol


Vitamin B-12 deficiency symptoms

Fatigue. B12-deficiency can cause overwhelming fatigue and tiredness. This may be accompanied by numbness or tingling of the extremities as well.

Megaloblastic anemia.  characterized by abnormally sized red blood cells and a lower cell count. Some of the telltale symptoms of megaloblastic anemia include shortness of breath, muscle weakness, nausea and paleness. Megaloblastic anemia caused by vitamin B-12 deficiency is referred to as pernicious anemia

Jaundice. This is often characterized by the abnormal yellowing of the eyes and skin, which is caused by the high amounts of the bilirubin pigment being released from the destruction of the fragile red blood cells brought on by low vitamin B12 levels.

Memory loss or cognitive difficulties. Studies show that the presence of low to normal levels of B12 in the body can lead to white matter damage in the brain, which then causes major impairment in cognitive function.




Researchers have discovered that B-12 deficiency generally occurs in four distinct stages:

Stage 1

Declining blood levels and cell stores.

Stage 2

Low cellular levels.

Stage 3

Increased blood level of homocysteine and a decreased rate of DNA synthesis.

Stage 4

Neurological disorders and in some cases cumulative damage due to long-standing deficiency may be irreversible. This impresses the importance of early diagnosis and ensuring adequate blood levels of vitamin B-12



If you suspect you have B-12 deficiency - get tested. You need an accurate baseline to work from. If you are B-12 deficient  you need to identify why - most likely with help  from your GP or a qualified nutritionist . Once the mechanism causing deficiency is identified then the appropriate action can be taken.

The first step is generally a blood test. Levels mostly considered normal are between 200ng/L & 650ng/L but experts who specialise in diagnosis and treatment of B-12 deficiency suggest 200ng/L is too low if patients present with symptoms & B-12 levels should not be less than 450ng/L

If  optimising your diet to contain higher amounts of B-12  the next step  can be difficult if you do not eat foods of animal origin as your choices are limited.

Vitamin B-12 comes from bacteria. Most grazing animals have multiple stomachs which contain bacteria that produce vitamin B-12  and whilst humans make vitamin B-12 in the colon it is too far down the intestinal tract to be absorbed.

Primates such as gorillas & chimps who eat a plant based diet obtain vitamin B-12 in a number of ways. Inadvertently they would eat many insects  and some primates also eat faeces neither option to most vegans is acceptable. These primates could also obtain B-12 from soil bacteria as they munch their way through unwashed vegetation, I think this is interesting and potentially it would be beneficial to eat your organic veg without scrupulously scrubbing away the soil, however this method is unlikely to be a reliable source of adequate B-12.


There are a variety of claims that certain plant foods contain B-12 including spirulina, nori, chlorella, tempeh and barley grass. Most studies, however,  have shown them to be inadequate to raise blood levels of B-12.  It is difficult to distinguish true B12 from analogues that can disrupt B12 metabolism. Even if true B12 is present in a food, it may be rendered ineffective if analogues are present in comparable amounts to the true B12. .

 Australian research has found B-12 present on button mushrooms surface which is bioavailable This could come from the growing medium. Some studies have also suggested shiitake mushrooms as a source.


B-12 can be harvested from bacteria and used in fortified foods and supplements, for vegans to ensure optimum levels of vitamin B-12 my preference would be for a supplement over a fortified processed food, because many of these foods are highly processed. One exception is Marigold Engivita yeast flakes made from inactive yeast without additives and can be very beneficial to help ensure adequate B-12 sprinkled over your meals.

Vitamin B-12 (also known as cobalamin) comes in different forms including cyano, methyl, deoxyadenosyl & hydroxy cobalamin. Supplements that contain  methylcobalamin are the ones to buy as this form is more easily utilized by the body, I recommend

If a mother is already B-12 deficient during pregnancy, a baby may be born with seriously low B-12 levels and develop clinical signs of deficiency as soon as two weeks. The general research suggests that even among non-vegetarians, B-12 can be insufficient in infants, and that perhaps all breastfeeding mothers should consider B-12 supplements for themselves and their infants during the time of breastfeeding. This lack of B-12 in the mother's diet during pregnancy has been associated with a lack of myelin production, which is the coating of the nerves. It takes somewhere between one to twelve months to develop, and manifests as failure to thrive and slow developmental progression.  Some vegans & vegetarians (who are the groups most likely to be deficient in B12) choose not to use fortified foods or supplements, however if you are breast feeding an infant, pregnant or seeking to become pregnant it is essential to ensure adequate B-12 in the diet.




J Agric Food Chem. 2009 Jul

Vitamin B12 is the active corrinoid produced in cultivated white button mushrooms (Agaricus bisporus).

Koyyalamudi SR1, Jeong SC, Cho KY, Pang G.


Eur J Clin Nutr. 2010 Sep

Serum concentrations of vitamin B12 and folate in British male omnivores, vegetarians, and vegans: results from a cross-sectional analysis of the EPIC-Oxford cohort study

Anne MJ Gilsing,  Francesca L Crowe,  Zouë Lloyd-Wright,  Thomas AB Sanders,  Paul N Appleby, Naomi E Allen,  and Timothy J Key


American Society for Nutrition

Vitamin B-12 and homocysteine status among vegetarians: a global perspective

Ibrahim Elmadfa and Ingrid Singer


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