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Observational epidemiological surveys (WG 3) page 13
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because of the results of intervention trials and the possibility that it is another fruit and
vegetable compound which is responsible for the risk reduction.
For stomach cancer, CNERNA, COMA and IARC agreed on the reduction of risk by
carotenoids. WRCF only said « possible » because there was no certitude that it is not another
fruit and vegetable compound which is responsible for the risk reduction. For larynx and
oesophagus cancers, results consistently showed a reduction of risk but there are few studies
which explain the « possible » of WCRF instead of the expected « probable ». For cervix
cancer, there are few studies, but they tend to agree with a reduction of risk. For colon and
rectum cancers, CNERNA, COMA and IARC agreed on the inconsistency of the results. The
WCRF sources indeed are very heterogeneous, in spite of the statement « possible ».
CNERNA and IARC found results on pancreas cancer more insufficient than inconsistent,
which was chosen by WCRF and COMA. CNERNA and IARC agreed on the inconsistency
of findings related to breast cancer. The « weakly consistent » of COMA was due to the
including carotenoids with vitamin A activity. This point demonstrates the difficulty of
assessing carotenoids in nutritional data base, since many of them evaluate carotenoids in
vitamin A equivalent. WCRF noted that one cannot ascertain that carotenoids are the marker
of other bioactive compounds. All of the four sources agreed to say that studies on prostate
cancer are too heterogeneous to bring any type of conclusion and that studies are insufficient
on ovary and endometrium cancers. Data are insufficient and/or inconsistent for all of the
other cancer sites.
Comparison between tables 2 and 5
The evidence that β-carotene is inversely associated to the risk of larynx, oesophagus, lung
and respiratory tract and stomach cancers was consistent. Thus it is possible that the reduction
of risk which is attributed to fruit and vegetables is mediated through carotenoids for these
cancers or alternatively that carotenoids are the markers of fruit and vegetables intake. For
bladder and pancreas cancers, data were insufficient. Colon, rectum, breast, ovary and
endometrium cancers appeared not related to carotenoids. Thus, the possible effect of
vegetables on the risk of these cancers might be not related to carotenoids.
1-1-5 Vitamin C (Table 6)
The conclusions of the three reference books, which are summarised in this part, do not
differentiate between dietary intake and plasma levels, and are presented as such in Table 6.