Lycopene observational studies

Etminan, M. et al.. The role of tomato products and lycopene in the prevention of prostate cancer a meta-analysis of observational studies. Cancer Epidemiol. Biomarkers Prev., 13, 340, 2004. 

The potential beneficial effects of lycopene in human health have been reviewed extensively in recent years [39-45] numerous observational studies have consistently shown an inverse relationship between the consumption of lycopene-rich diets (tomato or tomato-based foods) or plasma lycopene levels with the risk of cancers at various sites [46, 47]. The strongest inverse relationship was that for prostate cancer [2, 46-49], one of the most prevalent male cancers in the western populations and common across the world other significant inverse relationships were found with lung and stomach cancers. 

Lycopene in combination with vitamin E or vitamin D has been reported to potentiate inhibition of cancer cell growth. A synergistic effect was observed when physiologically relevant concentrations of a-tocopherol and lycopene were studied in various prostate cancer cell lines. Lycopene, in itself, was not a potent inhibitor of prostate carcinoma cell proliferation however, up to 90% growth inhibition was reported with the a-tocopherol and lycopene combined treatment. This synergistic effect was not shared by p-tocopherol, ascorbic acid, or probucol, indicating a nonantioxidant mechanism to be the basis of the finding. 

However, the overall picture is by no means as dark. To demonstrate this clearly, the evidence should be interpreted correctly. It is a fact that a diet with high levels of carotene is advantageous (Table 3.8). But a very high-dose consumption of purified carotenoids (especially p-carotene and vitamin A) is associated with higher risk for humans exposed to increased oxidative stress. General statements about the effects of carotenoids are impossible. For example, several studies showed that lycopene (the red pigment in tomatoes) rednces the risk of prostate cancer, and observational studies of tomato consumers revealed no side effects. 

Human observation studies using intermediate biochemical markers e.g., inverse relationships between lycopene intakes or its blood levels and biochemical markers, such as lipid or DNA oxidation products. 

Moreover, we recently reported that lycopene was able to enhance the arrest of cell cycle progression induced by TAR in RAT-1 immortalized fibroblasts. TAR-exposed cells treated with lycopene showed a delay in cell cycle at the G0/G1 phase and a concomitant reduction in S phase. Such effects were accompanied by a dose-dependent decrease in cyclin Dl levels. On the other hand, fibroblasts treated with lycopene alone showed the same effects, although to a lower extent. The down-regulation of cyclin Dl observed in this study was dose-dependent and occurred at lycopene concentration achievable in vivo after carotenoid supplementation (Palozza et al., 2005b). 

The observed associations between folate, antioxidant vitamins, and cardiovascular disease may be confounded by other substances in fruits and vegetables, as the following examples of studies show Flavonoids (see Chapter 31) are naturally occurring, water-soluble antioxidants found widely distributed in vegetables, fruits, tea, and wine. There is an inverse relationship between flavonoids and decreased risk of coronary heart disease. Lycopene, the key antioxidant in tomatoes, shows an inverse association with myocardial infarctions. There is an inverse association between folate and cardiovascular disease. 

Lycopene derived from a fungal biomass of Blakeslea trispos, suspended in sunflower oil at a concentration of 20% w/w, was tested for subchronic toxicity at concentrations of 0%, 0.25%, 0.50%, and 1.0% in rats for 90 days (Jonker et al., 2003). No evidence of toxicity of lycopene at dietary intake levels up to 1.0% was observed in this study. The authors suggest the noobserved-effect level (NOEL) for this lycopene to be 1.0% in the diet, the highest dietary concentration tested. McClain and Bausch (2003) published... 

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