The Bogus 'Science' of Secondhand Smoke
Tuesday, January 30, 2007; 12:00 AM
Smoking cigarettes is a clear health risk, as most everyone knows. But lately, people have begun to worry about the health risks of secondhand smoke. Some policymakers and activists are even claiming that the government should crack down on secondhand smoke exposure, given what "the science" indicates about such exposure.
Last July, introducing his office's latest report on secondhand smoke, then-U.S. Surgeon General Richard Carmona asserted that "there is no risk-free level of secondhand smoke exposure," that "breathing secondhand smoke for even a short time can damage cells and set the cancer process in motion," and that children exposed to secondhand smoke will "eventually . . . develop cardiovascular disease and cancers over time."
Such claims are certainly alarming. But do the studies Carmona references support his claims, and are their findings as sound as he suggests?
Lung cancer and cardiovascular diseases develop at advancing ages. Estimating the risk of those diseases posed by secondhand smoke requires knowing the sum of momentary secondhand smoke doses that nonsmokers have internalized over their lifetimes. Such lifetime summations of instant doses are obviously impossible, because concentrations of secondhand smoke in the air, individual rates of inhalation, and metabolic transformations vary from moment to moment, year after year, location to location.
In an effort to circumvent this capital obstacle, all secondhand smoke studies have estimated risk using a misleading marker of "lifetime exposure." Yet, instant exposures also vary uncontrollably over time, so lifetime summations of exposure could not be, and were not, measured.
Typically, the studies asked 60--70 year-old self-declared nonsmokers to recall how many cigarettes, cigars or pipes might have been smoked in their presence during their lifetimes, how thick the smoke might have been in the rooms, whether the windows were open, and similar vagaries. Obtained mostly during brief phone interviews, answers were then recorded as precise measures of lifetime individual exposures.
In reality, it is impossible to summarize accurately from momentary and vague recalls, and with an absurd expectation of precision, the total exposure to secondhand smoke over more than a half-century of a person's lifetime. No measure of cumulative lifetime secondhand smoke exposure was ever possible, so the epidemiologic studies estimated risk based not only on an improper marker of exposure, but also on exposure data that are illusory.
Adding confusion, people with lung cancer or cardiovascular disease are prone to amplify their recall of secondhand smoke exposure. Others will fib about being nonsmokers and will contaminate the results. More than two dozen causes of lung cancer are reported in the professional literature, and over 200 for cardiovascular diseases; their likely intrusions have never been credibly measured and controlled in secondhand smoke studies. Thus, the claimed risks are doubly deceptive because of interferences that could not be calculated and corrected.
In addition, results are not consistently reproducible. The majority of studies do not report a statistically significant change in risk from secondhand smoke exposure, some studies show an increase in risk, and ¿ astoundingly ¿ some show a reduction of risk.
Some prominent anti-smokers have been quietly forthcoming on what "the science" does and does not show. Asked to quantify secondhand smoke risks at a 2006 hearing at the UK House of Lords, Oxford epidemiologist Sir Richard Peto ¿ a leader of the secondhand smoke crusade ¿ replied, "I am sorry not to be more helpful; you want numbers and I could give you numbers..., but what does one make of them? ...These hazards cannot be directly measured."
It has been fashionable to ignore the weakness of "the science" on secondhand smoke, perhaps in the belief that claiming "the science is settled" will lead to policies and public attitudes that will reduce the prevalence of smoking. But such a Faustian bargain is an ominous precedent in public health and political ethics. Consider how minimally such policies as smoking bans in bars and restaurants really reduce the prevalence of smoking, and yet how odious and socially unfair such prohibitions are.
By any sensible account, the anachronism of tobacco use should eventually vanish in an advancing civilization. Why must we promote this process under the tyranny of deception?
Presumably, we are grown-up people, with a civilized sense of fair play, and dedicated to disciplined and rational discourse. We are fortunate enough to live in a free country that is respectful of individual choices and rights, including the right to honest public policies. Still, while much is voiced about the merits of forceful advocacy, not enough is said about the fundamental requisite of advancing public health with sustainable evidence, rather than by dangerous, wanton conjectures.
A frank discussion is needed to restore straight thinking in the legitimate uses of "the science" of epidemiology -- uses that go well beyond secondhand smoke issues. Today, health rights command high priority on many agendas, as they should. It is not admissible to presume that people expect those rights to be served less than truthfully.
Gio Batta Gori, an epidemiologist and toxicologist, is a fellow of the Health Policy Center in Bethesda. He is a former deputy director of the National Cancer Institute's Division of Cancer Cause and Prevention, and he received the U.S. Public Health Service Superior Service Award in 1976 for his efforts to define less hazardous cigarettes. Gori's article "The Surgeon General's Doctored Opinion" will appear in the spring issue of the Cato Institute's Regulation Magazine.