Today, another form of scientific illiteracy. The
University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
We all know salt is a major
contributor to heart disease, don't we? We know DDT
and chlorine cause cancer. We once knew that
electric fields caused leukemia. That knowledge has
largely evaporated, but salt and DDT still frighten
us. Coffee, cyclamates, and Alar have all been
called major carcinogens and later been cleared of
charges. Being called a carcinogen today is much
like being called a communist in 1954. If you were
called a communist, you were a communist until
you'd proven you weren't.
DDT is like that. Economist Tom DeGregori points
out it's a pretty benign chemical. During WW-II we
prevented typhus epidemics by DDT spraying, with no
side effects. Today it's called a "known
carcinogen" based upon almost no evidence. During
years of DDT use, liver cancer (which was blamed on
DDT) dropped by 32 percent. Hundreds of millions of
deaths from malaria and other insect-borne diseases
were prevented. DDT remains the cheapest safe
protection for most poor countries. Removing it
would mean major catastrophe.
While DDT hasn't been cleared as an environmental
threat, it has almost eliminated malaria in our
hemisphere. But then, most germicides and
pesticides come under attack sooner or later. The
natural element chlorine was removed from the water
supply in Trujilla, Peru, after a 1991 cancer
scare. The resulting cholera epidemic afflicted
almost a million people.
Now Gary Taubes writes about salt in
Science magazine. He titles his
article, The (Political) Science of Salt.
For thirty years we've been hearing that salt
increases the risk of heart attack. Medical
organizations have supported the claim up and down
the line.
The problem is, salt runs through our food chain
and is interwoven with fat in our diets. When we
examine data, the independent influence of
salt on blood pressure disappears. Taube calls the
controversy one between requirements of public
health policy and of good science. It started when
a 1972 study of rats linked salt to high blood
pressure. Since then half the studies suggest a
weak link, half show no link. Public health
organizations have accepted the first half and
ignored the second. And as experimental and
mathematical methods have improved, the link has
vanished.
DeGregori objects to popular media people making
national health policy. In the matter of salt, the
National Heart, Lung, and Blood institute is about
to convene yet another study panel. One noted
doctor says this time he hopes we'll "let
science drive the system rather than
opinions."
Of course it comes down to scientific literacy.
When we don't look to the methodical process of
scientific inquiry for knowledge, we lay ourselves
open to being misled over and over. The first and
last marker of scientific literacy has always been
doubt. Science means holding on to skepticism,
especially when we want to believe.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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