Thursday, November 5, 2009

cancer lurks in every shadow

This article, about the many chemicals we ingest and absorb, ought to leave you nicely paranoid about your own chances for getting cancer. Extract:

Let’s start with the bad news: You are saturated with man-made chemicals, some of them toxic. Today’s exposure began when compounds in your shampoo and shaving cream seeped into your skin cells, and during your morning coffee, when you drank chemicals that were released into your brew as hot water ran against the plastic walls of your coffeemaker. It continued all day as you touched industrial chemicals in packaging, or walked through pesticide-sprayed lawns, or cooked dinner on nonstick pans. This very minute, your skin is probably touching a piece of clothing or furniture that was doused in protective chemicals to make it resistant to microbes, fungus or water. Tonight, there’s a good chance you’ll curl up in sheets treated with flame retardants.

Some of these chemicals can stay in the body for decades, and in numerous studies over the past eight or so years, environmental toxins have been linked to everything from early puberty to cancer. David Servan-Schreiber, a founding member of Doctors Without Borders in the U.S. and a cancer researcher who survived the disease himself, summarized our predicament in the New York Times last year. “Since 1940, we have seen in Western societies a marked and rapid increase in common types of cancer,” he wrote. Since 1974, leukemia and brain cancer rates in children have risen by 28 percent.

Read the rest on your own. The article is about a guy who's trying to analyze all the chemicals in his system.



Bill said...

There are several things to keep in mind when doing the kind of broad epidemiologic reasoning that this guy is doing.

1. Some cancer death rates are because we now out-live other causes of death. We die from something--as accident, infectious disease, and cardiovascular death rates drop, so cancer death rates will rise.

2. Correlation is not the same as causation. This is part of the problem with the global warming controversy, there is a correlation between CO2 and average temperature, at least up until 1999, but the CO2 may have followed not preceded the higher temperatures. In the case of cancer incidence it may be covariant.

3. Causation can only be demonstrated by controlled studies. Those are extremely difficult to carry out on such issues as carcinogenesis.

4. Almost all demonstrations of carcinogenesis use orders of magnitude greater concentrations than can be found in the environment to induce the effect. Under such conditions, almost anything, including table salt can be shown to be carcinogenic. Such high concentrations are always cytotoxic, so the effect being found is not truly parallel to what is occurring in daily life.

5. Studies of carcinogenesis make a highly questionable assumption in their analyses--that the dose response relationship is linear all the way to zero exposure. From years of study of biological and chemical literature, I would consider this a false assumption. The actual relationship is most likely an S-curve. At some low level of exposure there is no effect.

Rather than cancer lurking in every shadow, fear and ignorance lurk in every shadow. Unfortunately, we don't do much to dispel the ignorance, which in turn would dispel much of the fear.

Bill said...

Sorry for the second post, but a comment on the original article reminded me that people play nasty games with statistics. They can skew them in their favor with mathematically correct, but analytically false calculations. The commentor picked the example of childhood leukemia statistics and pointed out the fact that large percentage change in the incidence did not translate into a large change in actual numbers. So call this item 6 in my preceding list.