Tomatoes, Lycopene, and Prostate Cancer

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Abstract
Summary The epidemiologic data tend to support an association between intake of tomato-based foods and a lower risk of prostate cancer. The observed inverse association may be due to lycopene though this is unproven at this point. Even two servings a week of a rich source of bioavailable lycopene, such as tomato sauce, was related to a substantially lower risk of prostate cancer. Whereas chance alone is highly unlikely to account for the consistent inverse association with tomato-based products, confounding by other variables, particularly dietary, cannot be definitively excluded as alternative explanations. Of greatest concern is that a lycopene-rich diet is acting as an indicator of a diet rich in vegetables and fruits that may lower risk of prostate cancer through other phytochemicals. An important historical lesson is provided by β-carotene, for which an abundance of evidence based on questionnaires and blood levels suggested a benefit on various cancers (93), particularly lung cancer, but recent intervention trials of β-carotene supplementation have not confirmed this benefit (60). In retrospect it appears difficult, if not impossible to differentiate β-carotene intake from that of a general dietary pattern that is high in fruits and vegetables. In contrast, this is not the case for lycopene. Other carotenoids in prostate tissue tend to be significantly interrelated, but lycopene content does not appear to be correlated appreciably with other carotenoids (83). In the Health Professionals Follow-Up Study and the Seventh-Day Adventist study, tomato-based products and lycopene were associated with a lower prostate cancer risk, but fruits and vegetables, individually and in aggregate, and other carotenoids were not associated with prostate cancer risk. These results are consistent with findings from other studies that overall vegetable and fruit consumption appear unrelated to prostate cancer incidence (36, 94, 95). It is more difficult to separate specific effects of lycopene from that of other potentially beneficial compounds in tomatoes; however, based on similarity of results for plasma predictors of lycopene with predictors of prostate cancer risk, the putative compound would be expected to have similar bioavailability characteristics as lycopene. Thus, with regard to practical recommendations, the available data are most conservatively interpreted as supporting a potential benefit of increased consumption of tomatoes and tomato-based products. To attribute a specific effect to lycopene or a particular isomer of this carotenoid would require much more research. Additional studies by epidemiologists, clinical investigators, cancer biologists, and nutritional scientists are underway, and answers to many questions concerning tomatoes, lycopene, and prostate cancer should be forthcoming.

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