Pro-vitamin A carotenoid conversion factors: retinol equivalents — fact or fiction?

The vitamin A potential of a food is conventionally expressed as retinol equivalents, i.e. retinol plus the corresponding retinol equivalent of the provitamin A carotenoids. 1 mg of β-carotene, for example, is taken to have the same biological activity as 0.167 mg of retinol. However, this figure is based on certain assumptions regarding the amount of β-carotene absorbed and subsequently converted to retinol. This commentary considers the numerous food and host related factors which may ultimately determine carotenoid bioavailability and conversion to retinol. The authors endorse suggestions that until more definitive data on the potential absorption of carotenoids from foods is available, any calculated value of the retinol equivalent of the provitamins must be treated with caution. Furthermore, we would suggest that the use of current data on retinol equivalents in tables of food composition should be abandoned.