Answer :Unlike many other nutrients, the Institute of Medicine has not established a Tolerable Upper Intake Level for vitamin B12, so theres no official point at which taking B12 becomes too much of a good thing. According to Jacob Selhub, PhD, director of the Vitamin Metabolism Laboratory at Tufts Jean Mayer USDA Human Nutrition Research Center on Aging, however, the bodys absorption of vitamin B12 is very limited, irrespective of dose. So theres no need to worry about overdosing on B12 in supplements or in food.
