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Small can be healthy

Toxins like radon and even DDT may have beneficial effects at very low doses.

Ursula Sautter | May 2008 issue

Arsenic

The notoriously toxic metalloid arsenic, found in the groundwater of some regions, is a known carcinogen. But recent studies suggest that when it’s consumed in minute concentrations, arsenic can reduce the risk of cancer. Geneticists from the Kolkata-based Indian Institute of Chemical Biology found that people who regularly ingest tiny amounts of the substance in drinking water are less likely to develop aberrant cells in their lymphocytes than people who aren’t exposed at all.

A 2004 study of bladder cancer mortality in the U.S. produced comparable results. A team of scientists from the School of Biological and Chemical Sciences at Deakin University in Burwood, Australia, and the New York University School of Medicine found a “protective effect against oxidative stress and DNA damage” when they treated human skin cells with small amounts of arsenite, one of the most common forms of arsenic.

DDT

DDT, a potential carcinogen, was banned in most countries and for most uses back in the 1970s, but traces of this pesticide (as well as others) can still be found in our food and our bodies. There is laboratory evidence that DDT boosts tumour growth in large doses. Research also suggests that at lower doses the substance may reduce abnormal tissue growth.

In 2005, pathologists at the University Medical School in Osaka, Japan, reported in Toxicology and Applied Pharmacology that DDT fed to rats in low doses inhibited the development of lesions in their livers. The researchers concluded this could be “related to changes in metabolizing enzymes, cell communication and DNA damage and its repair.”

Dioxins

Dioxins can be found in substances as diverse as herbicides, wood preservatives and car exhaust. It was the poison that almost killed Ukrainian politician Victor Yushchenko in 2004, leaving his face pocked and scarred. Trace amounts of dioxins routinely enter our bodies through the consumption of meat, fish, eggs and dairy products. One of the most harmful dioxins, TCDD, has been found to cause cancer in laboratory animals.

The same 1976 study that showed high doses of TCDD caused cancer in rats also demonstrated an anti-cancer effect when the chemical was administered in small amounts. More evidence of this effect was published in 2005, when a group at the National Public Health Institute in Kuopio, Finland, wrote in Dose-Response, “Moderately low exposures to dioxins could even decrease the risk of [soft-tissue sarcoma].” This is still a hypothesis, researchers stress, not a proven fact.

Hormesis has its critics, who argue that the potential benefits of low levels of toxins are due to random statistical fluctuations. Even if some substances do turn out to have positive effects in low doses, they point out, that shouldn’t distract from their harmful effects at higher doses. Indeed, no one suggests that popping low-dose dioxin pills—or exposing yourself randomly to any other toxin—is a good thing.

“It is also possible that some of these low-dose effects are in fact detrimental as well,” warns Dave Eaton, director of the Center for Ecogenetics and Environmental Health at the University of Washington in Seattle. “For example, low levels of DNA damage may well activate certain DNA repair pathways that increase the extent and possibly the efficiency of DNA repair. But it is still possible that some of the low-level DNA damage escapes repair and is ultimately detrimental. Thus I don’t think one can assume that all ‘low-dose’ responses are without potential harm.”

Still, if further research confirms the potential benefits of hormesis, Paracelsus’ old observation may acquire a new relevance.

Ursula Sautter is a freelance journalist living in Bonn, Germany.

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