Estimating the potential for vitamin A toxicity in women and young children.

This paper describes usual intakes of vitamin A from diet plus low dose supplements, reviews methods for assessing vitamin A toxicity and applies a kinetic analysis of vitamin A turnover to estimate the effect of high dose supplements on vitamin A liver stores in infants and young children. In the United States, the 95th percentile of intake by preschoolers from foods and supplements exceeds the tolerable upper level (UL) but is below the no-observed-adverse-effect level (NOAEL). The 95th percentile of vitamin A intake from foods and supplements for nonpregnant, nonlactating women aged 19-30 y also exceeds the UL but is below the NOAEL for women of reproductive age. In low income populations in developing countries, vitamin A intakes of preschoolers and women consuming foods plus low dose supplements can also exceed the UL but are unlikely to exceed the NOAEL. There are few data on which to establish thresholds for excessive vitamin A intake or vitamin A concentrations in tissues. To assess the potential toxicity of the new recommendations (see article by Ross in this issue) for high dose vitamin A supplements for infants and children, we used a kinetic approach to estimate accumulation of the vitamin in liver. The new recommendations are unlikely to result in toxic levels (>300 microg per gram of liver) even if high dose supplements are inadvertently given monthly. The kinetic analysis also illustrates that a constant supply of vitamin A from breast milk (and/or complementary foods) is vital for preventing depletion of liver vitamin A stores between high dose supplements.