Written By: Jerome Arnett, Jr., M.D.
Published In: Environment & Climate News
Publication Date: July 1, 2008
Publisher: The Heartland Institute
Exposure to secondhand smoke (SHS) is an unpleasant experience for many nonsmokers, and for decades was considered a nuisance. But the idea that it might actually cause disease in nonsmokers has been around only since the 1970s.
Recent surveys show more than 80 percent of Americans now believe secondhand smoke is harmful to nonsmokers.
Federal Government Reports
A 1972 U.S. surgeon general's report first addressed passive smoking as a possible threat to nonsmokers and called for an anti-smoking movement. The issue was addressed again in surgeon generals' reports in 1979, 1982, and 1984.
A 1986 surgeon general's report concluded involuntary smoking caused lung cancer, but it offered only weak epidemiological evidence to support the claim. In 1989 the Environmental Protection Agency (EPA) was charged with further evaluating the evidence for health effects of SHS.
In 1992 EPA published its report, "Respiratory Health Effects of Passive Smoking," claiming SHS is a serious public health problem, that it kills approximately 3,000 nonsmoking Americans each year from lung cancer, and that it is a Group A carcinogen (like benzene, asbestos, and radon).
The report has been used by the tobacco-control movement and government agencies, including public health departments, to justify the imposition of thousands of indoor smoking bans in public places.
EPA's 1992 conclusions are not supported by reliable scientific evidence. The report has been largely discredited and, in 1998, was legally vacated by a federal judge.
Even so, the EPA report was cited in the surgeon general's 2006 report on SHS, where then-Surgeon General Richard Carmona made the absurd claim that there is no risk-free level of exposure to SHS.
For its 1992 report, EPA arbitrarily chose to equate SHS with mainstream (or firsthand) smoke. One of the agency's stated assumptions was that because there is an association between active smoking and lung cancer, there also must be a similar association between SHS and lung cancer.
But the problem posed by SHS is entirely different from that found with mainstream smoke. A well-recognized toxicological principle states, "The dose makes the poison."
Accordingly, we physicians record direct exposure to cigarette smoke by smokers in the medical record as "pack-years smoked" (packs smoked per day times the number of years smoked). A smoking history of around 10 pack-years alerts the physician to search for cigarette-caused illness. But even those nonsmokers with the greatest exposure to SHS probably inhale the equivalent of only a small fraction (around 0.03) of one cigarette per day, which is equivalent to smoking around 10 cigarettes per year.
Low Statistical Association
Another major problem is that the epidemiological studies on which the EPA report is based are statistical studies that can show only correlation and cannot prove causation.
One statistical method used to compare the rates of a disease in two populations is relative risk (RR). It is the rate of disease found in the exposed population divided by the rate found in the unexposed population. An RR of 1.0 represents zero increased risk. Because confounding and other factors can obscure a weak association, in order even to suggest causation a very strong association must be found, on the order of at least 300 percent to 400 percent, which is an RR of 3.0 to 4.0.
For example, the studies linking direct cigarette smoking with lung cancer found an incidence in smokers of 20 to around 40 times that in nonsmokers, an association of 2000 percent to 4000 percent, or an RR of 20.0 to 40.0.