Bioavailability of and Interactions Among Trace Elements

With the advent of present-day tools and techniques of analysis, it is possible and practical to measure accurately the essential trace element content of human foods. Although this is a major step forward in assessing nutrient needs and status, an important unknown remains. To meet nutritional requirements it is important to know not only the quantity consumed but the proportion of that consumed which is absorbed and utilized. A major thrust of modern nutrition research is concerned with the absorption and utilization of nutrients in foods. The term bioavailability has been applied to this concept. Although bioavailability applies to and is an important consideration for all nutrients, it is particularly pertinent for the trace elements because so many factors affect their absorption and assimilation. Bioavailability of a specific trace element is affected by intrinsic factors such as the physiological status of the animal or person that consumes it. There are numerous intrinsic factors that significantly affect bioavailability (1), but this chapter is concerned with the extrinsic or dietary factors of importance in the bioavailability of those elements that are of prime concern in human nutrition. Extrinsic factors that affect bioavailability may be divided into major and minor dietary components. Furthermore, each of these components may be classed as an essential or nonessential nutrient. The minor components tend to interact more specifically with the essential nutrients. The purpose of this review is to describe interactions which determine bioavailability of iron, zinc, copper, and selenium. The reader is also referred to other reviews and symposia (1-6) related to the subject.