ABSTRACT
I. INTRODUCTION In the past few decades, dietary carotenoids have been implicated in biological processes that may have physiological relevance to human health and chronic disease. Some of the biological actions of carotenoids include antioxidant activity, intercellular communication, cell differentiation, immunoenhancement, and inhibition of mutagenesis and transformation. A variety of hypotheses concerning the potential role of carotenoids in health and disease arose from the effects of carotenoids observed in model systems in vitro and animal studies in vivo. Numerous epidemiological studies have also supported an inverse association between dietary intake or blood levels of carotenoids and risk of some chronic diseases. One of the most dramatic and consistent epidemiological observations from these studies was the inverse association between intake of fruits and vegetables high in β-carotene and lung cancer, which stimulated subsequent human intervention trials in high-risk groups of asbestos workers and smokers. The unexpected negative results that emerged from these trials brought into question the mechanisms of action of β-carotene and other carotenoids and their role in health and disease prevention.
