A critical review of minimal vitamin B6 requirements for growth in various species with a proposed method of calculation.

We conclude that vitamin B6 is efficiently conserved by the tissues and that the major dietary requirement is to meet physiological stresses such as growth, pregnancy, lactation, vigorous exercise, and/or disease. A reasonable approximation of the minimal requirement for growth in most species can be obtained by assuming 15 nmol vitamin B6 for each g gain in body weight. For birds and fish, which can achieve 1 g gain/g feed, the vitamin B6 content would need to be about 15 mumol (3 mg)/kg feed. Such an intake is achievable with a variety of natural diets and would also be adequate for most mammalian species, which have lower feed efficiencies. Although well-balanced natural diets are usually adequate, supplementation with 5-10 mumol (1-2 mg)/kg diet is inexpensive and would provide a safety factor to allow for variations in feed composition and physiological stresses such as pregnancy, disease, parasites, and so on. At this time, whether the metabolic changes associated with increases in vitamin B6 intake above the minimum confer long-term health benefits on the organisms is not clear. Excessive vitamin B6 intake can be toxic. Fish and prawn seem to be particularly sensitive to this toxicity. Additional work is needed to clarify the interactions between vitamin B6 requirements and protein intake.