Dietary intake of vitamin A is a combination of both pre-formed
and pro-vitamin A sources, but the bioavailability of different
sources varies between different forms. Pre-formed vitamin A,
such as retinyl palmitate, is absorbed rapidly, whereas provitamin
A carotenoids have poor absorption rates (Preedy, 2012).
Traditionally, vitamin A activity has been described in RE, which
takes into consideration the different bioavailabilities