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Small can be healthy

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

A glass of red wine after dinner a couple of times a week can help prevent heart disease; a nightly magnum of the stuff will corrode your liver. This is pretty much accepted wisdom. But what isn’t yet widely understood is that in very small doses, an array of substances considered toxic could potentially be good for you.

Take cadmium. This soft, blueish-white heavy metal, frequently used in batteries, is a known carcinogen. But studies on rodents suggest that in small doses, it can reduce cancer rates. Or consider mercury, a neurotoxin in fluorescent bulbs and thermometers; in tiny amounts, it has an antioxidant effect and can protect against cell damage.

The theory behind these phenomena is hormesis, a term derived from the Greek word hormo, “to excite.” The mechanism behind it is simple: A small dose of a toxin excites a stress reaction in the body, causing it to bolster its defences against the invader. This idea has been around since at least the 16th century, when Renaissance physician Paracelsus observed, “It’s the dose that makes the poison.”

In the 18th century, the German pioneer of homeopathy, Samuel Hahnemann, had the same notion. He believed remedies for diseases could be created by ingesting minute amounts of substances that cause symptoms of the disease.

It may not be surprising that some potentially harmful natural substances may have healthy effects at low doses. After all, the same principle underlies vaccinations, in which a tiny dose of, say, polio is administered so the immune system can build up resistance to it.

What’s more surprising is that the same may be true of man-made chemicals like dichloro-diphenyl-trichloroethane (DDT) and dioxins. These toxic substances can cause serious environmental and health problems, but research suggests that in small doses they can have positive effects. Hormesis “could be a major revolution across broad reaches of the biomedical world,” says toxicologist Edward Calabrese of the University of Massachusetts at Amherst, who found thousands of instances of the phenomenon in the scientific literature. “It would also be very important for drug discovery.” Here’s a look at some of the bad stuff that, in tiny amounts, might be good for you.

Radiation

The conventional view is that the higher the dosage of radiation, the greater the risk of cancer. Yet evidence is mounting that shows exposure to low-dose radiation can be a boon. For example, research into the long-term effects of the atomic bombs dropped on Nagasaki and Hiroshima in 1945 has found no indication that the attacks caused genetic damage. In fact, the frequency of leukemia among survivors exposed to relatively low-dose radiation was abnormally low.

A similar effect is seen in less dramatic cases of exposure. Reviewing scientific literature, Myron Pollycove, professor emeritus of laboratory medicine and radiology at the University of California at San Francisco, concluded in a 2007 article in the U.S. medical journal Dose-Response that “[p]opulations living in high background radiation areas and nuclear workers with increased radiation exposure show lower mortality and decreased cancer mortality than the corresponding populations living in low background radiation areas and nuclear workers without increased radiation exposure. … Both studies of cancer in animals and clinical trials of patients with cancer also show, with high statistical confidence, the beneficial effects of low-dose radiation.”

The impact of exposure to radon is a case in point. An odourless, tasteless and invisible radioactive gas produced from the natural breakdown of uranium in water, soil and rock, it’s often detected in building materials and causes thousands of lung cancer deaths per year. Yet several scientific studies suggest low levels of the element can decrease mortality from this type of cancer too. In 1993, researchers from Osaka found that residents of Misasa, Japan, where radon is plentiful, develop lung cancer less often than those in surrounding suburbs. A 1995 study conducted at the University of Pittsburgh also showed a correlation between higher radon levels and decreasing mortality rates from lung cancer.

Reviewing these and other papers, scientists at the Institute for Nuclear Science and Techniques in Hanoi, Vietnam, concluded in the 2006 International Journal of Low Radiation that “radon has been proven to decrease the lung cancer mortality rate at the low level.”

The secret behind the possible beneficial effects of low-level ionizing radiation—and other kinds of hormesis—appears to be cellular stress adaptation. Bombarded by radioactive substances, cells muster their defences to fend off damage.

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