Carotenoid functions in photoprotection and cancer prevention.

Carotenoid pigments in in vitro and in vivo systems are able to quench excited species, such as singlet oxygen and free radicals. The U.S. Food and Drug Administration has approved beta-carotene for use in humans for prevention of the photosensitivity associated with the orphan disease, erythropoietic protoporphyria. Although the usual adult dose used is 180 mg/day, intake up to 300 mg/day is allowed. No serious toxicity to beta-carotene has been reported. Carotenoids have demonstrated some anticancer activity in certain animals. Clinical trials in populations at high risk for developing certain types of cancer are presently underway, using doses of beta-carotene ranging from 15 to 50 mg/day, or much lower doses than used for photosensitivity prevention. There is no way of predicting which dose will be effective in preventing cancer: The lower doses were chosen to avoid development of marked carotenodermia; they are sufficient to cause an increase in the serum carotenoid level but may, occasionally, in individuals, cause the development of some degree of carotenodermia. This article reviews development of the use of beta-carotene for preventing photosensitivity in humans, studies investigating the anticancer properties of the carotenoids, and studies aimed at understanding how the carotenoids exert their protective functions.