A new Harvard School of Public Health study, published in the March 6 issue of the Journal of the National Cancer Institute, showed a lower risk of prostate cancer in men whose diets were rich in tomatoes and tomato-based products containing the antioxidant lycopene. Results were taken from the Health Professional Follow-Up Study, in which the dietary and health histories of 47,000 men, aged 40 to 75, were tracked for a period of 12 years. It was found that those who ate two or more meals a week containing tomato products reduced their risk of prostate cancer by 24 to 36 percent. The head researcher, Dr. Edward Giovannucci, said that these findings supported earlier studies linking foods such as fruits and vegetables with a lower risk of prostate cancer.
In the recent ACSH report, Risk Factors for Prostate Cancer, which evaluated and ranked the strength of scientific evidence for various lifestyle and dietary factors, lycopene was rated as a speculative protective factor with limited or conflicting scientific support. While it is an attractive idea that something as simple and well liked as tomato sauce could prevent prostate cancer, the scientific data, including the findings of this current study, do not conclusively support such a claim. The ACSH report states: "There is good reason to speculate that lycopene might be protective: this carotenoid is found in higher levels in the prostate than in most other body organs, and it has several biological actions, which might be cancer-protective. However, only some of the studies that attempted to relate men's lycopene intakes to their risk of prostate cancer found a relationship. Thus, the role of lycopene as a prostate cancer protective factor is still considered merely speculative."
The new Harvard study was most likely well done and carefully controlled but is not the strongest type of study. This descriptive study relies on dietary questionnaires as a source of data, and self-reporting is not always the most accurate form of data due to poor memory and/or misunderstanding of the questions. While this method can suggest hypotheses for future investigation, it cannot prove a causal relationship between lycopene and prostate cancer.
Finally, we should not assume that the positive effects shown in this study are due to only one component of a fruit or vegetable (such as lycopene in a tomato) that could easily be replaced with a supplement. Any real effect on prostate cancer might be due to the consumption of a combination of nutrients in lycopene-rich foods. Therefore, the conclusion that tomato-based products or lycopene lower the risk for prostate cancer is far from conclusive. In the press release, Dr. Giovannucci refers to a previous 1995 Harvard report, which produced similar results, as support of the hypothesis. However, this earlier report was based on the same study that is presented in the current report the only difference being that the earlier one used the preliminary data.
At the same time, there is nothing wrong with the recommendations Dr. Giovannucci and his colleagues are making to consumers to follow current health guidelines and increase their fruit and vegetable consumption. It is always a good idea to eat a sensible diet, one that includes moderate amounts of fat and meat and is high in fruits and vegetables, because such a diet plays a key role in fighting other health problems, such as heart disease and diabetes. However, men should not rely on lifestyle and dietary factors to protect them against prostate cancer. Until research proves otherwise, our top recommendation is that men, especially if they are at higher risk (if they're older, African-American, or have a family history of prostate cancer), should have regular checkups from their doctors.