Tomatoes, Lycopene, and Risk of Prostate Cancer

Like other carotenoids, lycopene can protect plants from photo-oxidation damage, but its role in humans is unclear. In the United States, tomatoes provide 85‐90% of dietary lycopene, with two-thirds contributed by tomato products. Tomatoes are also rich in vitamins C and A, folate, potassium, and several non-nutrient phytochemicals. Increased lycopene and tomato intake has been hypothesized to decrease the risk of prostate cancer, the most commonly diagnosed cancer among U.S. men. Of the 15 epidemiologic studies ‐ 3 prospective and 12 retrospective ‐ to evaluate this relationship, approximately half reported reductions in risk with increased intake (relative risks ~0.6‐0.8 between extremes of intake). Protective effects were most consistently seen with cooked tomato products, possibly because of enhanced lycopene bioavailability, and in U.S. white men. The three prospective studies of prediagnostic blood lycopene levels, a biomarker which integrates intake, absorption, and metabolism, and prostate cancer have also not concurred. However, they do suggest that risk may be reduced (relative risks ~0.5‐0.8) in U.S. white men, possibly because of relatively high circulating lycopene or linked dietary patterns and lifestyles. Thus, at present, epidemiologic research does not persuasively support or refute the protective promise of lycopene and tomatoes. Future research should focus on dietary and lifestyle determinants of blood lycopene levels, improved assessment of tomato product intake and incorporation of updated lycopene databases, direct measurement of lycopene in prostate tissue, and development of reliable intermediate markers of prostate carcinogenesis.