Vitamin B12 (Cobalamin)

Vitamin B12 is a very important vitamin: it’s key to the health of the central nervous system and is essential for the formation of blood cells and DNA.  
 
B12 deficiency can lead to (potentially irreversible) neurological damage and megaloblastic anaemia (when red cell count is low and the cells are larger the normal). 
 
It can take several years for vitamin B12 deficiency to manifest: the absence of symptoms should not be interpreted as a sign that supplementation is not required.  

No unfortified animal-free food has been shown to reliably increase vitamin B12 levels. And it is therefore mandatory for vegans to take a B12 supplement and/or consume B12-fortified foods.  

Supplementation has been shown to raise vitamin B12 levels in vegans to levels seen in non-vegans1.  

The table below (taken from veganhealth.org2) shows the requirements according to age and the dosing regimens one can adopt to meet these recommendations. 

The metabolism and absorption of vitamin B12 is rather complicated. These dosing regimens were created with the help of mathematician Stephen Walsh, who is affiliated with The Vegan Society. 

These recommendations only apply to cyanocobalamin (the form of vitamin B12 most commonly found in supplements).  

I think that taking a daily multivitamins and mineral supplement (that contains at least 5µg of B12) may be a more convenient option for many, as this can address other nutrients of focus (and thus can simplify supplement regimens).

Good vitamin B12 intakes are important for women who are planning to get pregnant as well as during pregnancy and lactation. Deficiency of this vitamin increases risk of irreversible neurological damage to baby.  Due to the lack of the scientific data on oral supplementation routines among vegan women and the possibility of newly absorbed vitamin B12 being more important for placental transport3 , daily intakes may be more appropriate. Veganhealth.org also suggests this option.
 
Although there is no established upper safe limit; it is widely believed that 1000mcg a day is a safe dose. I would advise against taking this amount daily for a prolonged period of time without discussing it with a doctor. 

If you opt to eat fortified foods or take low dose supplements several times per day, there should be a 4-6 hours gap between doses/meals. I fear that this may be impractical for many people and a single larger dose is a more convenient and reliable strategy. It is worth noting that taking vitamin B12 supplement on an empty stomach facilitates better absorption4.

After 50 the production on intrinsic factor drops and it seems sensible for older people to take a supplement whether they eat an animal-free diet or not. 

Other situations can also affect absorption of vitamin B12: pernicious anaemia; chronic or atrophic inflammation of the stomach; taking medication that suppresses stomach acid production like omeprazole, metformin; and smoking. These clinical situations may require higher doses under supervision of a doctor. 

Those who consume a lot of seaweeds (which I advise against) should not rely on standard blood tests for vitamin B12. It can be deceptive since seaweeds contain a lot of substances that look like vitamin B12 (analogues). These analogues are not able to fulfil the functions of vitamin B12. Under these circumstances, individuals should consider checking their levels of homocysteine or MMA (methylmalonic acid) in the blood. Elevated levels of either may suggest a vitamin B12 deficiency.  

References:

1.  Selinger, E., Kühn, T., Procházková, M., And?l, M. and Gojda, J., 2019. Vitamin B12 deficiency is prevalent among Czech vegans who do not use vitamin B12 supplements. Nutrients, 11(12), p.3019.   (https://www.mdpi.com/2072-6643/11/12/3019)    
2. https://veganhealth.org – Vitamin B12: Rationale for VeganHealth’s Recommendations
3. Rashid, S., Meier, V. and Patrick, H., 2021. Review of Vitamin B12 deficiency in pregnancy: a diagnosis not to miss as veganism and vegetarianism become more prevalent. European Journal of Haematology, 106(4), pp.450-455.  (https://onlinelibrary.wiley.com)
4. Berlin, H., Berlin, R. and Brante, G., 1968. Oral treatment of pernicious anemia with high doses of vitamin B12 without intrinsic factor. Acta Medica Scandinavica, 184(1?6), pp.247-258.

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