13-cis-β-Carotene-d5 is labelled 13-cis-β-Carotene (C184225) which is an isomer of β-Caroten (C184250). Carrots are one of the highest dietary sources of β-carotene and are naturally high in the (all-E)-β-carotene isomer, which has higher bioavailability, provitamin A activity, and antioxidant capacity compared to Z (cis) isomers.