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Observational epidemiological surveys (WG 3) page 46
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1-4 SYNTHETIC CONCLUSION
The conclusions of the reference books (CNERNA, 1996; WCRF, 1997; COMA, 1998) on
the protective effect of tomatoes on cancers of upper aero-digestive tract, as well as lung
and stomach are supported by the recent studies. Whether the tomatoes are raw, cooked or
processed was not precised in these studies. These cancers are those which are presenting a
lower incidence in subjects with high intake, or high plasma concentration of common
antioxidants, namely β-carotene and vitamin C (see tables 5, 6, 14-20). However, lycopene,
the specific carotenoid of tomato, which is a powerful antioxidant (see group one) was not
associated to these cancer sites (upper aero-digestive tract, plus lung and stomach) in six
studies out of 8 (significantly inversely associated with oesophagus and mouth and pharynx
cancers). Although the difficulty in assessing lycopene intake and plasma concentrations has
to be kept in mind, these observations suggest that it is not lycopene which is responsible for
the protective effect of tomato against upper aero-digestive tract, as well as lung and stomach
cancers, but the other compounds present in tomatoes, β-carotene and vitamin C, and
possibly phenolics. These compounds might act additively or synergistically (see table 16,
Yong et al., 1997). Thus, it is the food as a whole which is most likely to be protective, and
this may be extended to food habits or typology.
So far, no effect of tomatoes on other cancers has been demonstrated except for the
suggestion of a protective effect of cooked tomatoes against prostate cancer (Giovanucci et
al., 1995, Key et al., 1997; Tzonou et al., 1999). This suggests a role for lycopene since
cooking and processing tomatoes concentrates lycopene and makes it more absorbable,
whereas vitamin C is decreased in cooked and processed tomatoes. Again, in five studies
investigating the relationship of lycopene and prostate cancer, two, the Health Professional
Study and the Physicians Health Study (Giovanucci et al., 1995; Gann et al., 1999), showed a
risk reduction for prostate cancer, especially in aggressive cases. However, vitamin E has
been shown protective against prostate cancer in a case-control study (Tzonou et al., 1999,
see Table 22), in two prospective studies based on plasma concentrations, especially in
smokers (Eicholzer et al., 1996; Gann et al., 1999, see table 25) and in an intervention trial
(Heinonen et al., 1998). Vitamin E present in tomato seeds is generally kept out from the
edible part or excreted, but vitamin E-rich vegetable oil is often used to prepare canned
processed tomato sauce and home cooked tomatoes. Thus, a confounding might occur, since