News - Tiny doses can be dangerous

Tiny doses can be dangerous
By Elizabeth Weise
From USA Today, 04/24/03
Page 2D

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.