The recommended dietary amount of vitamin B-12 for people age 14 and up is 2.4 micrograms per day, according to Mayo Clinic. Pregnant women require 2.6 micrograms of vitamin B-12 daily, while breast-feeding mothers need 2.8 micrograms per day.
Children require much smaller doses than adults, advises Mayo Clinic. Children from ages 1 to 3 need 9 micrograms of vitamin B-12, while children from 4 to 8 years need 1.2 micrograms. Children ages 9 through 13 need a 1.8 microgram dose.
Doctors recommend people age 50 and over meet their recommended dietary intake through foods rich in vitamin B-12 or via a supplement of 25 to 100 micrograms, reports Mayo Clinic. When used for treating vitamin B deficiency, doctors sometimes recommend up to 2,000 micrograms of vitamin B-12.