Conversion of carotenoid to vitamin A is rarely 100% efficient and the potency of foods is described in retinol activ ity equivalents(RAE): 1 ug of retinoi is equivalent to 12 Hg B-carotene, or 24 ug of other carotenes. Retinol in turn can be converted to retinal and retinoic acid. Liver, fish oil. egg yolk, butter, and milk are good sources of preformed retinol and retinoic acid.