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β-Carotene and the Immune Response

There have been consistent findings in over thirty epidemiological studies that high intakes of carotenoid-containing foods and high serum @-carotene levels are associated with lower incidences of certain cancers, especially lung cancer. One possible mechanism for the chemoprevention may be enhancement of immune responses (Bendich & Olson, 1989). The immuno-enhancement may be due to an increased vitamin A status from provitamin A carotenoids, or involve the antioxidant and singlet oxygen-quenching capacities of carotenoids having nine or more conjugated double bonds or involve other mechanisms as yet undetermined. The present review examines the effects of carotenoids on many aspects of immune function in normal animals as well as in tumour-bearing animal models with the objective of elucidating the non-vitamin A effects of carotenoids. In addition, the recent findings of direct effects of carotenoids on decreasing malignant transformations are discussed.