Secondhand sickness
The headlines say it all:
"Passive smoking risk overstated"...
"Passive smoking may not damage your health after all"...

The reports stem from a May paper published in the British Medical Journal (BMJ) that claimed there is no, or very little, relationship between passive smoking and cancer. For the study, researchers James Enstrom and Geoffrey Kabat looked back on a well-known study originally commissioned by the American Cancer Society. The study, which followed the habits and health of 118,904 Californians for 39 years beginning in 1959, has been used to understand the epidemiology of several cancers but never, until now, applied to passive smoking.

Enstrom and Kabat paid close attention to what happened to the 35,561 participants who had never smoked but were married to someone who smoked. The model assumes that "never smokers" married to smokers will have more exposure to secondhand smoke than other individuals. Accordingly, if secondhand smoke poses a real threat to health, "never smokers" married to smokers should be more likely to get sick, on average, than "never smokers" married to nonsmokers.

But in fact, Enstrom and Kabat found no such link. Rather, they concluded that there is no statistically significant link between secondhand smoke and deaths from coronary heart disease, lung cancer or chronic obstructive pulmonary disease (COPD).

"The results do not support a causal relation ..., although they do not rule out a small effect," the researchers -- who declined our requests for an interview -- wrote.

The paper clashes with the hundred or so studies in BMJ and other medical journals in recent years that do report a link between secondhand smoke and disease. But, as BMJ editors pointed out in an accompanying editorial, the new paper is hard to dismiss, by virtue of having so many participants.

Despite this strength, the paper's authors have faced a storm of criticism. The British Medical Association called the study "flawed" and pointed out the "overwhelming evidence" showing a link between secondhand and lung cancer, heart disease and as a trigger for asthma in children.

Another objection is that secondhand smoke was far more common, in public places as well as in homes, in the 1960s and 1970s than it is now. As a result, the "never smokers" married to nonsmokers in the study may have been exposed to enough ambient secondhand smoke to be at risk of disease.

Along similar lines, being married to a smoker doesn't necessarily mean being exposed to any volume of smoke. The association may exist, but many researchers suspect the controversial study overestimated it. This uncertainty is a persistent problem in studies of passive smoking.

Lastly, as the authors acknowledged in the paper, they were largely funded by tobacco industry grants. It is not the first time industry-funded research has dismissed the threat of passive smoking.

Just last December, BMJ published an account ( see "How the tobacco industry responded..." in the bibliography) of the tobacco industry's response to a 1981 Japanese study showing an association between passive smoking and lung cancer. According to the BMJ report, tobacco companies sponsored a new study designed to disprove the original, and "tried to hide its involvement in refuting the [original] study."

The researchers who designed and executed the study included a tobacco industry scientist, a tobacco industry consultant, and an industry law firm. The paper, not surprisingly, concluded there is no evidence that exposure to secondhand smoke increases the risk of lung cancer. But what may surprise you is that many of the primary contributors -- those with industry ties -- were never listed as authors on the final paper. This kind of "ghost" authorship is increasingly common in studies funded by corporations. But critics say it's a misleading practice, leaving gaps where credit and accountability should be.

Courtesy The Richard W. Pollay 20th Century Tobacco Advertising Collection.

Not in my face
Critics of the Enstrom and Kabat paper are quick to point out that their study should not be dismissed merely because they received industry support. But the overwhelming consensus of health researchers and organizations remains: Passive smoking is bad for you, and for your children. Both the World Health Organization and the Centers for Disease Control have issued impassioned statements warning of the risks of secondhand smoke.

The authors of a new study say warnings about the dangers of secondhand smoke have gone too far. Others disagree. AP Photo/Jim Mone

The carcinogens in tobacco smoke have been found in "passive smokers" -- at far higher levels than in people who are not exposed to smoke. And more than 40 studies of people who were married to smokers (many of which do not share the design flaws of the Enstrom paper) show that in all, passive smokers have around a 20 percent increased risk of disease, compared with people in nonsmoking households. One of these studies, known as the CPS-II, which was conducted by the American Cancer Society, followed nearly a million people for 14 years.

What's more, researchers at the Cincinnati Children's Hospital in the Medical Center of Ohio found last year that exposure to secondhand smoke in childhood is linked with lower cognitive abilities, even after factors such as poverty and the level of education of the parents were controlled for. Reading scores, for example, declined by about one point for every nanogram of cotitine (a breakdown product of nicotine) present in a child's blood.

Join the growing quitter's club.

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