Vitamins — How Much Is for Keeps?

An evaluation of the adequacy of dietary intakes of nutrients requires not only knowledge of the nutrient content of the foods ingested but also the extent to which the nutrient present in the diet is available for absorption and utilization, that is, its bioavailability. What is meant by bioavailability? Bioavailability is considered to be the relative absorption of a nutrient from the diet, but this definition may be extended to include the relative accumulation of a nutrient into storage pools and various tissues. Obviously, nutrients ingested but not released during the digestive process for absorption and utilization have no nutritional value. Thus, overall bioavailability may refer to the degree to which a nutrient becomes available to the target tissue after ingestion from the diet.1