One-time graded doses of vitamin A to weanling piglets enhance hepatic retinol but do not always prevent vitamin A deficiency

Background: Vitamin A supplements are administered to infants in developing countries at immunization contacts; doses of 50 000 IU vitamin A are recommended. Doses of 100 000 IU are given to children aged 0.5-1 y. The efficacy of these doses has not been adequately determined. Objective: We aimed to quantify liver vitamin A after the administration of vitamin A doses to piglets. Piglets are a good model for infants because of their similar size, gastrointestinal anatomy, and vitamin A requirements. Design: Castrated male piglets born to sows fed a vitamin A-depleted diet throughout 1 (parity A) or 3 (parity B) pregnancy and lactation cycles were randomly assigned to receive 1 of 4 oral vitamin A doses (ie, 0, 25 000, 50 000, or 100 000 IU) at weaning (days 9-14). A vitamin A-depleted diet was fed until the piglets were killed on day 10. Serum retinol was measured on days 1, 2, 4, 7, and 10. The modified relative dose response was measured before supplementation and at the time of killing, and liver vitamin A concentration was measured. Results: In both parities, 25 000 IU did not result in a mean liver retinol reserve > 0.07 μmol/g liver (the deficiency cutoff). The 50 000-IU dose increased mean reserves above 0.07 μmol/g only in parity A. Liver vitamin A reserves with the 100 000-IU treatment were only 5% above those with the 50 000-IU treatment. The modified relative dose-response test reflected differences in liver vitamin A stores in parity B, and the 0-IU group differed significantly from the 100 000-IU group (P = 0.011). Conclusion: This piglet model suggests that, for supplementation to infants <6 mo old, a 50 000-IU dose is likely to be more efficacious in mitigating deficiency than is a 25 000-IU dose.