Newsletter 02 2006.pdf - Sight and Life

NEWSLETTER 2/2006
21
SIGHT AND LIFE
Prof. Erdman’s collaborators.
Once the trial studies are assembled
and sorted, those that meet
inclusion criteria are rated for
quality in terms of design, inclusion/exclusion
criteria, balance
of population characteristics
across groups, verification of
compliance with the intervention
and appropriateness of statistical
analysis. This is done for each
study. The CARIG audience was
particularly intrigued to learn that
any study without a “validated”
dietary intake method would be
excluded from consideration. For
those who know the limitations
of dietary method validation/calibration,
this seems fraught with
arbitrary possibilities.
The pre-final step is to rate the
overall strength of the body of
evidence in terms of type, quality,
quantity and studies’ sample size,
consistency and replication of
findings, and the relevance to the
US general population or target
subgroups. Finally, the claim can
have three degrees of ranking: 1.
conclusive; 2. limited; or 3. very
limited.
The modifications in the FDA
procedures derive from the tension
among consumers’ desire to
preserve health, producers’ and
retailers’ desire to exercise free
speech, and the government’s
duty to protect the citizenry from
consumer fraud. Dr. Ellwood’s
message had shown that the role
of the scientific community lies in
how well they design and execute
studies on causal relationships
between a dietary substance and
a beneficial outcome.
Prof. John Erdman of the University
of Illinois also spoke in the
second session of the program
with a talk entitled: Tomato, Lycopene
and the Risk of Prostate
Cancer. He was also awarded
this year’s Wilbur O. Atwater
Memorial Lecture, sponsored by
the United States Department
of Agriculture on 4 April, which
had the theme of carotenes at its
center. His award’s lecture topic
was Colors, Critters, and Cancer.
As he explained, the colors refer
to carotenoid pigments; the critters
refer to the selection (limits
and possibilities) with different
animal models for investigation
of carotenoid metabolism and
effects; and cancer is specifically
prostate cancer. The context is
the epidemiological evidence that
suggests that tomato consumption
is protective against prostate
cancer.
The world of colorful carotenoids
contains over 650 compounds.
Phytoene and phytofluene are
simple colorless precursor carotenoids.
All known members of
this family of compounds are initially
synthesized in plant tissues;
animals cannot form carotenoids.
Prof. Erdman reminded his audiences
that the ripeness of fruits
John Erdman
and vegetables is reflected in
their carotenoid content. Carotenes
contribute to the hues
of birds’ feathers and insects’
coloring. Moreover, carotenes are
important to aroma compounds
in nature that have importance for
interspecies signaling.
Not all animals handle carotenoids
in a uniform fashion.
It has been found for instance
that, for studies of carotenoid
metabolism related to human
physiology, gerbils, ferrets and
pre-ruminant calves provide the
best in likeness to human absorptive
systems. They are capable
of absorbing the compounds
both intact and metabolized. As
herbivores, rats and mice are efficient
converters of provitamin A
carotenoids. They are poor at
absorbing intact carotenoids;
thus, high feed levels are needed
for these rodents to replicate the
tissue concentrations achieved in
humans. In Prof. Erdman’s view,
the armamentarium of animal
models for cancer studies with
carotenoids includes rats, mice,
and again ferrets.
The prostate gland and carotenoid-containing
foods came
together in the observations of
vastly different spontaneous incidence
rates for prostatic cancer
with 70 times greater incidence
rates in North American blacks
and 50-fold increased rates