Lycopene, tomato products, and prostate cancer prevention.
Have we established causality?*
Elizabeth C. Miller1, Craig W. Hadley2, Steven
J. Schwartz2, John W. Erdman, Jr.3, Thomas W.-M.
Boileau4, and Steven K. Clinton1, **
1Division of Hematology and Oncology, Ohio State University,
Columbus, OH 43210, USA; 2Department of Food Science and Technology,
Ohio State University, Columbus, OH 43210, USA; 3Division of Nutritional
Sciences, University of Illinois, Urbana, IL 61801, USA; 4Department
of Human Nutrition and Food Management, Ohio State University, Columbus,
OH 43210, USA
Abstract: The relationship between tomato products
and prostate cancer prevention has been the subject of increasingly
intense research activity over the past decade. The hypothesis that
tomato products contain phytochemicals, perhaps lycopene and others,
that modify prostate carcinogenesis warrants investigation. However,
scientists, regulatory agencies, marketers of products, and those defining
public health policy have differing opinions regarding the strength
of the data when applied to criteria for inference and causality. It
is useful to briefly review these criteria and discuss the relative
strengths and weaknesses of the published data in order to better define
future directions for research. Accepted categories of criteria include:
consistency, strength of association, biological gradient, temporality,
specificity, biological mechanisms and coherence, and experimental evidence.
We believe that continued support for research regarding tomato products,
lycopene and other phytochemicals, and prostate cancer risk is warranted
and may ultimately serve as the basis for more consistent public health
recommendations for the consumer. But, what do we say to the public
when the data is still inconclusive? The authors support the recommendation
that a minimum of five servings of fruit and vegetables should be consumed
daily from a variety of sources. We believe that the hypothesized benefits
of tomato products for prostate cancer prevention may be achieved with
approximately five servings of tomato products per week. The consumption
of lycopene supplements is not currently recommended for prostate cancer
prevention or therapy. Future research will allow us to provide more
** Corresponding author.
*Lecture presented at the 13 th International Symposium
on Carotenoids, Honolulu, Hawaii, USA, 6-11 January 2002.
Other lectures are published in this issue, pp. 1369-1477.