Hormesis Theory:
Tiny Bits of Toxins Do Affect People

Tiny doses of toxins and radiation in the environment, 
once ignored as insignificant, affect people's health in good and bad ways

SETH BORENSTEIN / Knight Ridder 27feb04

WASHINGTON—Tiny doses of toxins and radiation in the environment, once ignored as insignificant, affect people's health in good and bad ways, scientists are finding.

In some cases—such as most types of radiation and cancer-causing dioxin—tiny exposures may benefit people, according to a scientific theory that's growing in acceptance. The hormesis theory is that small doses of a toxin can make a human cell grow stronger.

In other cases—such as lead and tiny particles of soot—new research indicates that doses once considered insignificant sometimes make people sick.

Whether small doses of toxins are beneficial or harmful seems to depend on what the substances are, how small the doses are, what diseases are being studied and who's exposed to them.

One thing toxicologists agree upon these days is that small doses of toxic substances really do matter. Findings in this developing science will dramatically change how society weighs the risks of pollution and existing environmental and public health regulations. It also will affect thinking about which pollution most needs to be cleaned up.

"The real question is what is happening at low doses as opposed to what is happening at high doses," Linda Birnbaum, the Environmental Protection Agency's director of experimental toxicology and incoming president of the Society of Toxicology, said in a news briefing this week.

A National Academy of Sciences study on the health effects of low-level radiation—including possible beneficial effects—is due late this year. It is expected to give the most comprehensive and independent look to date at small dose issues.

Edward Calabrese, a toxicology professor at University of Massachusetts in Amherst, is the driving force behind the new look at the effects of small doses of toxic chemicals. The once-discredited theory, hormesis, is making its way into mainstream science and will be a central topic at next month's Society of Toxicology conference in Baltimore.

The idea behind hormesis is that parts of human cells change when challenged with small doses of toxins. These changes often make the cell stronger at first, but larger doses can still damage it. It is similar to the immunity-building effects produced by small and weakened doses of viruses used in vaccines, Calabrese said.

With the help of a $900,000 Air Force contract, he's developed a database of 6,000 studies that he says show hormesis effects.

Some, Calabrese says, show that low levels of dioxin—a group of cancer-causing chemicals that are byproducts of burning and industrial activities—reduce liver tumors. Other studies suggest health benefits from low doses of non-radon radiation.

"The blanket statement that low doses can be helpful is wrong," said Peter deFur, an environmental studies professor at Virginia Commonwealth University who serves on an EPA's chemical advisory board. "There's no evidence to support that what's actually happening is actually good for you."

Birnbaum said Calabrese's work doesn't look at how low doses of toxins can accumulate in a body to become bigger and harmful doses. And, she said, it doesn't take into account that different toxins in the body interact in new and harmful ways.

Calabrese acknowledges these limitations. "The idea that low doses of things may have a good effect is something we have to be very, very careful about," Birnbaum said.

source: http://www.charlotte.com/mld/observer/news/8053453.htm 27feb04