**4. Conclusions**

*Z*-Isomerization of carotenoids can cause changes in the bioavailability, antioxidant activity, and other functionalities (such as anticancer and antiatherogenic activities), and it may result in "positive" or "negative" effects, which vary according to the type of carotenoid. Although more than 1100 carotenoids are found in nature, only the eight carotenoids discussed above have been investigated in terms of these effects. Thus, further progress in this research area is expected. Furthermore, most investigations have focused on the effects of *Z*-isomerization of carotenoids on the bioavailability and antioxidant activity, but the *Z*-isomerization has been shown to enhance the anticancer and antiatherogenic activities of β-carotene and fucoxanthin. Since these data provide important evidence for the roles of carotenoid *Z*-isomerization in human health, examination of other carotenoids is expected in the future.
