The apparent conversion factor (x) for calculating the amount
of retinol equivalents provided by provitamin A carotenoids from
fruit or vegetables was estimated by using the following formula:
Change in serum retinol concentration of retinol-rich group/
mg retinol + (mg carotene/x) provided to retinol-rich group =
change in serum retinol concentration of fruit or vegetable group/
mg retinol + (mg carotene/x) provided to fruit or vegetable group
(1)
where mg carotene = mg all-trans-b-carotene + 0.5 3 mg
a-carotene + 0.5 3 mg b-cryptoxanthin + 0.5 3 mg cis-isomers