Cell Phones, Cancer, and Secondhand Smoke

A huge study released just this week shows no evidence that cell phones trigger cancer. Scientists tracked 420,000 Danish cell phone users, including 52,000 who had used them for 10 years or more and some with 21 years of usage. Matching these names against the Danish Cancer Registry, which records every citizen who gets the disease, the researchers found cell phone users were no more likely than anyone else to get cancer of various types. This result was really no surprise since at least 13 previous studies had come to the same conclusion.

Epidemiologists evaluate danger on a scale of “relative risk.” (Relative risk is also known as risk ratio, or RR.) On this scale, the number 1.0 indicates no effect. Higher numbers indicate higher risk, and numbers below 1.0 indicate a beneficial (protective) effect rather than danger. Cell phones, computers, electric blankets, and hair dryers all have RRs of 3.0 to 4.0, and none of these devices has been found to cause cancer. The municipal water supplies that tens of millions of Americans drink every day in thousands of U.S. cities have RRs 2.0 to 4.0, and no danger of cancer has been found from them. And EPA declined to regulate high-voltage power lines because it said the relative risk seldom exceeded 3.0. But both EPA and the U.S. Surgeon General claim that secondhand tobacco smoke with a RR of 1.19 (EPA's number) or 1.2 to 1.3 (SG's number) is a serious health hazard! (See my earlier blog posting “Surgeon General Trades Integrity for Advocacy” July 16, 2006 and my other postings on secondhand smoke.)

If secondhand smoke really is dangerous, why does it have a RR so much lower than cell phones, computers, electric blankets, hair dryers and municipal water supplies, which aren't dangerous? And the differences are much greater than you might think. Consider, for example, two RRs: one of 1.2 and the other 2.0. The latter would seem to be less than twice the former (67 percent greater, actually)—but the risk is actually five times greater. Here's why: a RR of 1.2 means a risk of 20%, and a RR of 2.0 means a risk increase of 100%. And 100% is five times greater than 20%. So, the tens of millions of Americans who drink municipal water with a RR of 2.0 are incurring a risk five times greater than that posed by secondhand smoke with an RR of 1.2, and the risk is fifteen times greater for the millions more who drink municipal water with RR of 4.0. And the risk from secondhand smoke is only one-tenth of that for a RR of 3.0. (Cell phones RR is actually slightly higher than that; so the risk from secondhand smoke is slightly less than one-tenth of that from cell phones.) And cell phones aren't dangerous. Secondhand smoke is even less so. In fact, a large number of studies show secondhand smoke with a RR of less than 1.0, particularly for children.