NB: 1 international unit (IU) = 0.3 retinol equivalents (RE); 1 RE = 1 µg retinol = 0.0035 µmol retinol.
The current RDA for men is set at 900 RE (3,000 IU).
Acute toxicity occurs when adults and children ingest > 300,000 IU and > 60,000 IU over hours to days.
Chronic toxicity occurs with daily intakes of more than 100,000 IU for more than 6 months, or more than 25 000 IU for more than 6 years.
References
Penniston KL, Tanumihardjo SA. The acute and chronic toxic effects of vitamin A. Am J Clin Nutr. 2006 Feb;83(2):191-201 PMID 16469975.
Institute of Medicine, Food and Nutrition Board. Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, molybdenum, nickel, silicon, vanadium, and zinc. Washington, DC: National Academy Press; 2001:65-126.