In our modern sanitary world, vitamin B12 is found reliably only in animal products, supplements, and B12-fortified foods. Vegetarians and vegans are recommended to take supplements containing at least 50 mcg of cyanocobalamin (the most stable form2452) a day or at least 2,000 mcg once a week2453 (or brush twice daily with a B12-fortified toothpaste2454).
