Vitamin B12 Sources And Recommendations

Vitamin B12 is not made by plants or animals. B12 is made by bacteria. These vitamin B12-producing bacteria can be found in soil, the roots of plants, the gut of animals and even in the human gut. Unfortunately for us, our B12-producing bacteria are located in a specific lower part of our gut where we cannot absorb the vitamin, which is consequently lost in our feces. For this reason, some animals get their B12 via coprophagy – consuming their feces. Animals store the B12 produced by their gut bacteria in their muscles and liver, or secrete it via the milk. We humans are fully reliant on our diet for B12, with animal products being the main source.

If we don’t consume enough B12, we might feel tired or weak, but over time, this deficiency can result in dementia, depression, memory loss, and even psychosis. Getting enough B12 is particularly important during pregnancy and while breastfeeding, whereas too little B12 can have major consequences for the developing baby. We do store substantial amounts of B12 in the liver, which can delay symptoms for up to 10 years after insufficient intake.

All The B12 That You Need

Our body needs between 2.4 and 4 microgram (μg) B12 per day, however not all B12 that we consume is actually absorbed. The absorption of B12 is an interesting process. Per meal or dose, we can only uptake 1.5 – 2 μg, due to a limited number of receptors that can bind B12. After that, we need about 6 hours before we can uptake more B12. In addition to this active uptake, about 1% of any given dose is absorbed by a process called passive diffusion. That effectively means that only about 10 μg of a 500 μg oral supplement is absorbed in healthy people. On a plant-based diet, it is highly recommended to take an oral supplement of 250 μg or higher per daily dose, even though lots of foods (especially dairy-free milks) are B12-fortified.  

B12 supplements are sold in various forms: cyancobalamin, methylcobalamin, deoxyadenosylcobalamin and hydroxocobalamin There is currently no consensus on which form is better. In foods hydroxy-, methyl- and deoxyadenosyl-cobalamin are the main cobalamins present. Cyanocobalamin, a synthetic form of B12 which is rarely naturally present is food, is often used in supplements since it is more stable. Eventually all cobalamins are converted into methylcobalamin and deoxyadenosylcobalamin, the forms which are used by our body.

references

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Degnan, P. H., Taga, M. E. & Goodman, A. L. Vitamin B12 as a modulator of gut microbial ecology. Cell Metab. 20, 769–778 (2014)

European Food Safety Authority. Scientific Opinion on Dietary Reference Values for cobalamin (vitamin B12). Available at: https://www.efsa.europa.eu/sites/default/files/consultation/150310a.pdf

European Food Safety Authority. Scientific Opinion on 5’-deoxyadenosylcobalamin and methylcobalamin as sources for Vitamin B12 added as a nutritional substance in food supplements. (2008). Available at: http://www.efsa.europa.eu/sites/default/files/scientific_output/files/main_documents/815.pdf

Food and Drug Administration. Food Labeling: Revision of the Nutrition and Supplement Facts Labels. (2016). Available at: https://www.federalregister.gov/documents/2016/05/27/2016-11867/food-labeling-revision-of-the-nutrition-and-supplement-facts-labels

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National Institutes of Health. Vitamin B12 Fact Sheet for Health Professionals. (2018). Available at: https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/

Thakkar, K. & Billa, G. Treatment of vitamin B12 deficiency-methylcobalamine? Cyancobalamine? Hydroxocobalamin? – Clearing the confusion. Eur. J. Clin. Nutr. 69, 1–2 (2015)

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Watanabe, F., Yabuta, Y., Bito, T. & Teng, F. Vitamin B₁₂-containing plant food sources for vegetarians. Nutrients 6, 1861–73 (2014)