Tiny doses can be dangerous
By Elizabeth Weise
From USA Today,
A saying among toxicologists is ''The dose
makes the poison.'' The assumption was that most everything was safe if
there were only a little of it.
But new scientific work is
beginning to show that the adage may be wrong and that extremely low
levels of certain chemicals are more dangerous than we knew.
Some chemicals are what are
known as ''endocrine mimics.'' That means the shapes of their molecules
are very similar to hormones that the body produces naturally, so they
readily fit into the hormonal receptors sprinkled around the body.
In high doses, these
chemicals simply swamp those hormone receptors. Once they fill them all
up, the system is maxed out, so a higher dose doesn't have any additional
effect. In testing, this makes it look as if there's no greater effect
above a certain level. But it's turning out that the real effect is at
extremely low doses, doses that are much closer to the tiny amounts the
body itself produces to signal hormonal and reproductive changes.
Because of this, there's
concern that high-dose testing is misleading because it has created the
belief that extremely low doses are safe. But in fact, scientists have
found in some instances that doses in the range of the natural hormones --
doses previously thought to be safe -- can have striking effects,
especially on reproduction and development.
2003 USA TODAY, a division of Gannett Co. Inc.