Vitamin B12 is an important nutrient as it plays a large role in red blood cell production, health of our nerves and brain health. Deficiency in B12 can lead to many health problems including anemia and neurological issues. 40% of the general public has been shown to be deficient in B12 consumption making this not just a "vegan issue" but a public health issue.
Let’s talk about where this vitamin comes from. B12 is a vitamin produced by bacteria in the soil. No animal/human produces enough B12 on its own and that’s why it is important to make sure we get enough. Originally, humans could get B12 from rain water, well water and from the bacteria on fruits and vegetables. Now we live in a very sanitized world, where water is chlorinated, fruits and vegetables are triple washed, and pesticides are highly utilized. All good measures as they save a lot of lives and help protect us from other pathogenic bacteria. However, this process also kills the bacteria that produce B12.
Safest way to get enough B12 is supplementing with a B12 supplement. Similar to how most humans are not able to get B12 naturally, animals in animal agriculture don't either. The animals in the animal agriculture get supplemented with B12. By supplementing with B12, you are cutting out the middle man (meat).
B12 supplement recommendation is to supplement with at least 2000mcg cyanocobalamin once a week. People 65 years of age or older should supplement 1000mcg every day.
References:
Ankar, A. Vitamin B12 Deficiency (Cobalamin). StatPearls. 2019.
Vitamins, 6. B Vitamins. Ullmann's Encylcopedia of Industrial Chemistry. 2012.
Tucker, K.L. Plasma vitamins B-12 concentrations related to intake source in the Framingham Offspring Study. Am J Clin Nutr. 2000.
Schubach, R. Micronutrients status and intake in omnivores, vegetarians and vegans in Switzerland. Eur J Nutr. 2017.
Vitamin B12: Fact Sheet for Health Professionals. NIH.
Greger M. Vitamin B12: how much, how often? 2011 Aug 30.
https://ods.od.nih.gov/factsheets/vitaminb12-healthprofessional/
https://www.agric.wa.gov.au/livestock-biosecurity/cobalt-deficiency-sheep-and-cattle