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Vitamin B12 - What are the Facts

Karen Scobie


Vitamin B12 is a remarkable vitamin. It is actually needed in smaller amounts than any other known vitamin. It has been shown that we only need around 10 mcg per day to supply the body with all it needs. It can take 5 years or more to develop a deficiency in adults, although some people can experience problems within one year and for others it could be up to 20 years depending on their stores. 

Vitamin B12 will not be supplied in sufficient amounts on a whole food plant based diets. Herbivores, like sheep and cows, can absorb vitamin B12 via their own digestive tract, but for humans, although it has been shown we can make vitamin B12 via the microorganisms within our gut, we cannot reabsorb it back through the gut wall. We therefore, need to be absorbing it from our food, or taking a supplement. Many foods, like cereals and non-dairy milks, are now fortified with vitamin B12 and it is possible to get your recommended daily allowance from this type of food. 

It is not a forgone conclusion that because you eat animal products that you will automatically be absorbing vitamin B12. Whether you can absorb vitamin B12 depends on how good your stomach and small intestine environment are and whether you are producing enough intrinsic factor. According to research there are more meat eaters with a vitamin B12 deficiency than those who are on a plant based diet, mainly due to the fact that they supplement it. 

There are many foods in the plant kingdom that have certain levels of vitamin B12 such as spirulina, nori, tempeh, barley grass etc, but the claims that they are a suitable non-animal sources of vitamin B12 for humans, hasn't stood the test of time. In over 60 years of vegan experimentation only vitamin B12 fortified foods and vitamin B12 supplements have proven themselves as a reliable sources which are capable of supporting optimal health. 

The organisms that create vitamin B12 are the microbes that blanket the Earth. This shows you how fundamental bacteria are to human existence. These bacteria grow in the guts of animals, which is why their bodies and products can be a source of this vitamin. Herbivores get all they need from ingesting insects, bacteria, dirt and faeces. We may once have gotten all we needed by drinking out of mountain streams and well water, but our water is now chlorinated to kill off bugs and bacteria. We also live in very clean environments, with antibacterial wipes, sprays, soaps and bleach. In our sanitised world those on a plant based diets must ensure that they get a regular reliable source of vitamin B12. 

What are the signs of deficiency? Fatigue and regular pins and needles in the fingers and toes are signs of longterm deficiency which can lead to elevated homocysteine and methylmalonic acid (MMA) levels. Even slightly elevated homocysteine levels is associated with increased risk of many health problems including heart disease in adults, preeclampsia during pregnancy and neural tube defects in babies. Clinical deficiency can cause anemia or nervous system damage. 

Earlier we noted that meat eaters are also at risk of deficiency and this is usually due to the digestive systems inability to absorb vitamin B12. Anyone over the age of 50 should look at supplementing vitamin B12 as research has shown that our stomach acid declines as we age. Try the stomach acid test from last months Fatburn Boost to check yours. Stress also lowers stomach acid and many people are now on medications that stop stomach acid production completely. No stomach acid means no intrinsic factor, which means no vitamin B12 absorption. 

We can help our stomach acid production by looking at all of these. Apple cider vinegar has been shown to help improve the stomach environment. Taking a couple of teaspoons of organic apple cider vinegar in some warm water 10 mins before food may help improve your overall digestive ability. Celery juice has also been shown to improve the ability to increase stomach acid production.

Most plant based eaters have been shown to have adequate levels of vitamin B12 to make clinical deficiency unlikely but nonetheless show restricted activity of vitamin B12 related enzymes, leading to elevated homocysteine levels. Strong evidence has been gathered over the past decade that even slightly elevated homocysteine levels will increase the risks of heart disease, stroke and pregnancy complications. 

How much vitamin B12 do we actually need? Latest research is suggesting that we need between 4 and 7 micrograms per day. We only absorb 1.5 mcg at a time. If we take a weekly supplement of 2500 mcg we will immediately absorb 1.5 mcg into our receptors and then 1% of the remainder of the 2500 mcg will diffuse passively right through our gut into our bloodstream. This will give us almost a week’s supply. We could take up to 3000 mcg at one sitting to make sure that we are completely covered for the week. Anymore than that and we would just pee it out. Even although it is a water soluble vitamin we don't have to take it everyday because we have evolved to work with such small amounts and our body has devised a way to hold on to it. 


Andres, E., Loukili, N. H., Noel, E., et al. (2004). Vitamin B12 (Cobalamin) Deficiency in Elderly Patients. CMAJ. Aug 3;171 (3): 251-9 

Doscherholmen, A. and Hagen, P. S. (1957). A Dual Mechanism of Vitamin B12 Plasma Absorption. J. Clin. Invest. Nov; 36 (11): 1551-7 

Allen, L. H. (2009). How Common is Vitamin B12 Deficiency? Am. J. Clin. Nutr. Feb; 89 (2):693S-6S. Carmel, R. and Jacobsen, D. W., (2001). Homocysteine in Health and Disease. Cambridge University 

Press, ISBN 0-521-65319-3. 

Institute of Medicine (US ), (1998). Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6,Folate,VitaminB12,PantothenicAcid,BiotinandCholine. NationalAcademyPress,ISBN0-309- 06554-2. 

Norris, J. (No Date). Vitamin B12: Are you getting it? Available at: (Accessed: 25 October 2016)