Factors Affecting the Bioavailability and Metabolism of Vitamin A and Its Precursors

Abstract

In dealing with the problem of vitamin A deficiency in preschool children, the dietary intake required to satisfy the needs of a child for growth and the prevention of clinical symptoms of vitamin A deficiency should obviously be defined. At first glance, we are seeking a specific number, which appears to be a simple, easily resolvable task. In actuality, it is not a simple task at all, because the number keeps changing as a result of five major factors: 1) the bioavailability of vitamin A and its precursors in the diet, 2) nutrient interaction, 3) the presence, length, and severity of disease, 4) metabolic parameters — and in particular storage efficiency, the turnover of reserves, and recycling efficiency, and 5) statistical considerations. I wish first to consider each of these major factors, and then to suggest a new approach to vitamin A nutriture which might allow simplification of many of the complexities involved in assessing their importance.