From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Thu Sep 11 2003 - 21:21:58 MDT
On Thu, 11 Sep 2003, Robbie Lindauer wrote:
> We KNOW that the pollutants cause cancer.
To a limited extent -- we know that certain pollutants can cause
mutations (this has been worked out extensively by Bruce Ames).
But this can include both pollutants *and* natural substances.
What we don't know is the effect of dose-response relationships.
There is reasonable evidence that exposure to low levels of stresses
or toxic substances might actually up-regulate cell defenses and
decrease the chances of getting cancer. This process is known as
hormesis.
> We don't KNOW that age does.
Ca-ca. Cancer rates go up with age whether one lived in Roman
times or the 20th century.
> Although it seems tautological - if increased exposure to pollutants
> causes cancer, then the longer you are exposed to them, the more
> likely you are to get cancer, hence the older you are, the more
> likely you are, etc.
No argument -- except for the hormesis effect I point out above.
This is very variable in the human population -- consider humans
living in a cave (for generations) with high radon levels vs. humans in
a cave with low radon levels. It would have been very difficult for evolution
to do a complete population optimization for exposure to variable levels
of ionizing radiation (radon is radioactive and decays producing radiation
that is potentially a major source of lung cancer).
> While the conjecture is an important one, it doesn't make it more than
> a contributing factor - GIVEN that we KNOW that increased stress,
> pollutants, alcohol, tobacco, smog, heavy-metals, food-poisons, etc.
> are cancer-causing.
Stress causes cancer because it down-regulates the response of the
immune system (see Sapolsky's work). This is a general misprogramming
of the genome and the shift we have had from a hunter-gatherer societies
to modern societies (which do provide certain benefits like antibiotics).
Pollutants is kind of a genaral term -- certainly some alter gene regulation
pathways in very subtle ways -- such as pollutants that resemble natural
hormones (which seem to be involved in serious consequences to the development
of certain fish and amphibians). Other pollutants may be completely harmless.
Tobacco and smog are complex problems because they are not specific substances.
Again types of molecules may be harmful but others may be non-harmful or
even beneficial.
Heavy metals can disrupt normal genetic regulatory pathways or the function
of normal protein functions (as was recently determined for cadmium).
They may or may not cause cancer. Iron and copper can hardly be considered
"heavy" metals but both are ions that if not properly managed can generate
free radicals that *will* damage DNA and lead to cancer. They are also
essential nutrients -- if not consumed in sufficient quantities one is
highly likely to suffer a premature death. Ha -- you can beat cancer
by reducing your iron and copper intake -- that way you die before you
get a chance to develop cancer.
Certain "food-poisons", such as Sulforaphane in Broccoli actually have
anti-cancer properties by up-regulating the better pathways of detoxification
in ones liver.
Bottom line (IMO): a big chunk of aging is due to the misrepair of DNA
double strand breaks corrupting the genetic code. The longer you are around
the more corrupted the code becomes. Result: increased rates of cancer
and the more general phenomena known as "aging".
This fits in well with oxidative stress, management of cellular glucose
levels (the whole glycemic index thingy), caloric restriction, increases
in mutagenic substances in the environment damaging DNA, exposure to higher
radiation levels (homes with higher radon levels), etc.
Bottom line -- one isn't going to correct the problem until one has robust
bionanotechnology or nanotechnology to correct the repair pathways that
cause the corruption of the genetic code. The best you may be able to do
in the meantime is retard those processes that contribute to the mutations
and/or double strand breaks.
Robert
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