For people over 14 years of age, 2.4 mcg is the recommended daily intake for vitamin B-12. Thus, any supplement that gives you a higher dosage should meet the requirements (15). Also, be mindful of the vitamin B-12 you will be consuming through food products like eggs, beef, and tuna. It is best to follow the manufacturer's suggestion or the expert of medical opinion while deciding the dose of a vitamin B-12 supplement.