Lycopene and prostate cancer risk. Methodological considerations
in the epidemiologic literature*
Channing Laboratory, Department of Medicine, Brigham
and Women's Hospital and Harvard Medical School, 181 Longwood Avenue,
Boston, MA 02115, USA; Departments of Nutrition and Epidemiology, Harvard
School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA
Abstract: Prostate cancer is the most common cancer
in U.S. males. Among potentially beneficial natural compounds is lycopene,
which is derived largely from tomato-based products. Recent epidemiologic
studies have suggested a potential benefit of this carotenoid against
risk of prostate cancer, but not all of the studies have been supportive.
The largest prospective dietary study, the Health Professionals Follow-Up
Study (HPFS), had found that 2-4 servings of tomato sauce per week were
associated with about a 35 % risk reduction of total prostate cancer
and a 50 % reduction of advanced prostate cancer in follow-up from 1986
to 1992. Tomato sauce was by far the strongest predictor of plasma lycopene
levels in this study. In the largest plasma-based study, high lycopene
levels were associated with similar risk reductions for total and advanced
prostate cancer. Results from other studies, mostly dietary case-control
studies, have been mixed. The reasons for these inconsistencies are
unclear. Because lycopene may come from a number of sources, and the
bioavailability of lycopene may vary profoundly across these sources,
dietary questionnaires are likely to vary markedly in their utility
to estimate true variation in body lycopene stores across individuals.
With further follow-up in the HPFS, we addressed some possibilities
for apparently conflicting results. We confirmed our initial findings
with the independent 19921998 follow-up period. Our results also
indicated various factors may contribute to some of the inconsistencies,
including insufficient sample size, low intake of lycopene, failure
to account for bioavailability, reliance on a single dietary assessment,
and heterogeneity of prostate cancer.
*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.
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