Is It Safe Yet to Have an Honest Conversation About Secondhand Smoke and Lung Cancer?

Several years ago I was talking
to an epidemiologist who is skeptical of the idea that smokers pose
a mortal threat to people in their vicinity. Although he supported
workplace smoking bans, he was frustrated by the willingness of so
many anti-tobacco activists and public health officials to overlook
or minimize the weakness of the scientific case that secondhand
smoke causes fatal illnesses such as lung cancer and heart disease.
He wondered when it would be possible to have a calm, rational
discussion of the issue, one in which skeptics would not be
automatically dismissed as tools of the tobacco industry. I
suggested that such a conversation might take place once smoking
bans became ubiquitous, at which point the political stakes would
be lower. Judging from a
recent article in the Journal of the National Cancer
Institute, headlined “No Clear Link Between Passive Smoking
and Lung Cancer,” that conversation may have begun.

The article describes a large prospective study that “confirmed
a strong association between cigarette smoking and lung cancer but
found no link between the disease and secondhand smoke.” The study
tracked more than 76,000 women, 901 of whom eventually developed
lung cancer. Although “the incidence of lung cancer was 13 times
higher in current smokers and four times higher in former smokers
than in never-smokers,” says the JNCI article, there
was no statistically significant association between reported
exposure to secondhand smoke and subsequent development of lung
cancer. “We don’t want people to conclude that passive smoking has
no effect on lung cancer,” says one of the researchers, Stanford
oncologist Heather Wakelee. “We think the message is, this analysis
doesn’t tell us what the risk is, or even if there is a risk.”

While hardly the last word on the subject, the study has
advantages over most of the research commonly cited as evidence
that secondhand smoke causes lung cancer. “To our knowledge,” the
authors say, “this is the first study to examine both active and
passive smoking in relation to lung cancer incidence in a complete
prospective cohort of US women.” The prospective design avoids a
weaknes of studies that start with lung cancer cases and “match”
them to controls. “Many studies that showed the strongest links
between secondhand smoke and lung cancer were case–control studies,
which can suffer from recall bias,” notes the JNCI
article, since “people who develop a disease that might be related
to passive smoking are more likely to recall being exposed to
passive smoking.”

Even more revealing than the study’s findings are the comments
from experts quoted in the article (emphasis added):

Jyoti Patel, MD, of Northwestern University School of Medicine
said the findings were not new….

“Passive smoking has many downstream health effects—asthma,
upper respiratory infections, other pulmonary diseases,
cardiovascular disease—but only borderline increased risk of lung
cancer,” said Patel. “The strongest reason to avoid passive
cigarette smoke is to change societal behavior: to not live in a
society where smoking is a norm.“

In other words, although the U.S. Centers for Disease Control
and Prevention will
tell you that “secondhand smoke causes an estimated 3,400 lung
cancer deaths among U.S. nonsmokers each year,” scientists have
long understood that the actual number might be closer to zero. The
basic problem is that the doses of carcinogens absorbed by
nonsmokers are much lower than the doses absorbed by smokers, so
any lung cancer risk would be correspondingly small and therefore
hard to detect using the blunt tools of epidemiology. The
associations found in studies of secondhand smoke and lung cancer
(which generally involve wives of smokers) are weak, meaning it may
be impossible to rule out alternative explanations. But none of
that really matters, Patel says, because the main goal of smoking
bans was “to change societal behavior” by stigmatizing smoking,
making it less convenient and less socially acceptable. Indeed,
even if you accept every allegation about the hazards of secondhand
smoke, it’s clear that the real “public health” payoff from smoking
bans, in terms of reducing tobacco-related morbidity and mortality,
comes from shrinking the number of smokers.

That is not what advocates of smoking bans said, however. Their
main rationale was always protecting bystanders, and they never had
any patience for the distinction between public and private
property, or the notion that people who choose to enter a bar or
restaurant where smoking is allowed thereby consent to any risk
posed by exposure to secondhand smoke. The warning that “secondhand
smoke kills,” with lung cancer as the paradigmatic
example, played an important role in the debate over
government-imposed smoking bans. By raising the stakes, it helped
transform a complaint into a right, so that people annoyed by
tobacco smoke now felt justified in demanding that it be eliminated
everywhere they might want to go, including other people’s
property. As another expert quoted
in JNCI article puts it, “We’ve gotten
smoking out of bars and restaurants on the basis of the fact that
you and I and other nonsmokers don’t want to die. The reality is,
we probably won’t.” Now they tell us.