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Observational epidemiological surveys (WG 3) page 10
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may appear inconsistent or weakly consistent if all types of vegetables are considered. It has
to be noted that several studies attributed the risk reduction effect of vegetables specifically to
vegetable fibre.
1-1-3 Lycopene (Table 3)
1-1-3-1 studies based on dietary intake
The specific effect of lycopene was never considered in the COMA. There are very few data
on dietary lycopene and cancers in the two other reference books.
Table3: Level of evidence of protection provided by studies on
dietary intake of lycopene and cancers*
cancer sites CNERNA
WCRF
Carotenoids
(France, 1996) (USA, 1997) (I A R C, 1998)
lung and
NM NM inconsistent
respiratory tract
1:-; 2: (-); 1: 0
pancreas insufficient
1: -
NM NM
breast NM NM insufficient
1: 0
prostate insufficient** insufficient inconsistent
1: (+); 1-
1:(+)1:-
1:-; 3: 0.
*the figures indicate the number of studies, -: a significant risk reduction; (-): a non
significant risk reduction; 0: no relationship; + an increased risk.
**the study showing an increased risk of prostate cancer with high intake of lycopene,
was significant only when papaya was the source of carotenoids.
NM: Not Mentioned
The data were scarce and inconclusive. However, studies based on lycopene intake are
hampered by lack of availability of complete and reliable food composition tables, which
might explain the unexpected inconsistency of the relationship between lycopene intake and
lung and respiratory tract cancers. Alternatively, it might be that compounds other than
lycopene are responsible for a protective effect of tomatoes.
1-1-3-2 Studies based on plasma levels (Table 4)
Neither CNERNA nor COMA reported on plasma levels of lycopene and cancers. They were
summarized in the IARC book and were shown to be too few to draw any conclusions except
for breast (inconsistent) and skin (no relationship) cancers (Table 4). However, it is known
that lycopene is characterised by unstability and fast turnover in plasma (see WG2), and this
might explain these inconclusive results.
Table 4: Level of evidence of protection provided by
studies on plasma lycopene and cancers*