The Vitamin A activity of beta-carotene compared to that of retinol is?
Beta-Carotene (provitamin A): 

This is found in plant foods. lt is cleaved in the intestine to produce two moles of  retinal.
ln humans, this conversion is inefficient, hence beta-carotene possesses about  one-sixth vitamin A activity compared to that of retinol.

Reference: Satyanarayana- Biochemistry, 3rd edition, pg-119
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