β-Carotene (Provitamin A) is a naturally-occurring retinol (vitamin A) precursor obtained from certain fruits and vegetables with potential antineoplastic and chemopreventive activities. As an anti-oxidant, beta carotene inhibits free-radical damage to DNA.

Glucoraphanin, the precursor of the widely extolled chemopreventive agent sulforaphane found in broccoli, has antioxidant activity.