The role of carotenoids on the risk of lung cancer.

Smoking prevention and cessation remain the primary methods of reducing the incidence of lung cancer. The limited success of efforts towards smoking cessation have led to increasing interest in the role of nutrition in lung cancer prevention. One class of nutrients that has attracted attention as potential chemopreventive agents is the carotenoids, especially beta-carotene, due to their antioxidant properties. In vitro, carotenoids exert antioxidant functions and inhibit carcinogen-induced neoplastic transformation, inhibit plasma membrane lipid oxidation, and cause upregulated expression of connexin 43. These in vitro results suggest that carotenoids have intrinsic cancer chemopreventive action in humans. Many cohort and case-control study data have shown an inverse relationship between fruit and vegetable consumption and lung cancer, although several more recent studies have cast doubt on these findings. Different effects of various dietary nutrients on lung cancer risk have been observed. Several prospective intervention trials were undertaken to examine the effect of supplementation on the risk of lung cancer. Some of these studies demonstrated an increased incidence and mortality from lung cancer in those receiving supplementation. Many hypotheses have emerged as to the reasons for these findings.