Could tomato (or lycopene) prevent prostate cancer?
The intake of cooked tomatoes, and the lycopene they contain, is associated with decreased risk of prostate cancer in several major epidemiological studies.
Rodents - In a fist animal model of prostate cancer, Imaida et al (2001) found no significant protection afforded by 15 to 45 ppm lycopene in dimethylaminobiphenol induced rats. However, a close look at their data shows that lycopene-fed rats had three-times less carcinoma than controls, in two independent studies (1/18 and 2/19 incidences vs. 8/23 in first study; 3/17 and 2/16 vs. 8/23 in second study). These data are consistent with a protection.
Boileau et al (2003) showed that freeze-dried tomato powder clearly protected the methylnitrosourea-testosterone-treated rats: the hazard ratio was 0.74 with 95%CI = 0.59 to 0.93. In contrast, 161 ppm lycopene had no effect (N.S. 9% decrease in mortality). The methylnitrosourea-testosterone treatment induces carcinoma in the dorsolateral and anterior prostate, which may be closer to human cancer than the ventral location induced by dimethylaminobiphenol. Further analysis of these data shows that tomato powder and pure lycopene significantly decreased the hazard risk for prostate cancer death by 56% and 44% respectively, after 45 wk (both p<0.05).>
Humans - No definitive clinical trial was done in humans yet. However, at least three small scale intervention studies were conducted in volunteers. Together, they give convincing evidence that tomato sauce, or lycopene, shrinks prostate cancer in humans.
H-1- The proportion of apoptotic cells increased three-fold in the prostate carcinoma of 32 patients given tomato sauce for 3 weeks (30 mg lycopene/d), compared with pre-treatment value (Kim, N&C 2003). However, the difference with control patients not given tomato did not reach significance. The same study shows that tomato sauce significantly reduced the level of serum prostate-specific antigen (PSA), and the level DNA oxidative damage in the prostate (Chen JNCI 2001; Bowen, EBM 2002).
H-2- Fifteen prostate cancer patients given tomato oleoresin extract (30 mg lycopene/d) for 3 weeks had smaller tumors (80% vs. 45% less than 4 ml), and lower level of invasion of both prostatic and extra-prostatic tissues, compared with subjects in the control group (N=11). In addition, the intervention reduced PSA levels (Kucuk, CEBP 2001).
H-3- The third study involved 54 prostate cancer patients for two years. They all underwent orchidectomy, and half of them were given 4 mg lycopene/d via two capsules. Each LycoredTM capsule contains: lycopene 2mg, vitamin A palmitate 2500 I.U., alpha-tocopheryl acetate 10 I.U, vitamin C 50 I.U, zinc sulphate monohydrate 27.45 mg, monohydrated selenium dioxide 70 µg (Dr R.N. Gupta, personal communication). Several tumor markers, including PSA levels, uroflowmetry and bone scans were significantly improved in the lycopene group. Strikingly, 12 patients died in the control group, but seven only in the lycopene group (p<0.001)>
Conclusion on lycopene and prostate- These studies support the hypothesis that tomato reduces the risk of prostate cancer. No direct evidence is given that lycopene alone has chemopreventive properties. One rat study points out that whole tomato is protective, but not pure lycopene. Human studies were done with tomato sauce or extracts, or lycopene mixed with other antioxidant molecules. Animal and human studies fit together, but they were done simultaneously: In this ongoing success story, rodents studies were not "predictive", since rats results were not known before humans trial were set up.
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