Teratogenicity of vitamin A.

There are few documented reports in humans that link teratogenic consequences to high intakes of supplemental R or RE, taken either acutely or chronically. This is in contrast to the well-documented teratogenicity in humans of RA and some of its synthetic derivatives. Both R and RE are documented teratogens in animals. Therefore, until more is known about the mechanisms of placental transfer and control as well as about the dose-related teratogenicity of vitamin A at different stages of gestation, there are few justifications for routine ingestion by fertile women of supplemental vitamin A in excess of 8-10,000 IU. Exceptions are when clinical signs are evident and habitual diets are unusually deficient. Even then, however, high dosages should be restricted to single administrations followed by frequent or daily dosages not exceeding 10,000 IU. Available evidence indicates that high-dosage supplements of beta-carotene can be safely taken; the dosages probably should be of a level to sustain blood concentrations below 300 micrograms/dl.