Study Strengthens Cancer Link to Secondhand Smoke : Health: Exposure during both childhood and adulthood poses greatest risk. Tobacco industry disputes findings.
In the largest and most comprehensive study of its kind, researchers in four states reported Tuesday that long-term exposure to secondhand cigarette smoke can increase the risk of lung cancer in nonsmoking women by as much as 86%, and that women exposed both during childhood and adulthood were particularly at risk.
Experts said the five-year study, which appears in today’s Journal of the American Medical Assn., provides the best proof to date that secondhand smoke is associated with an increased risk of lung cancer, and backs the U.S. Environmental Protection Agency’s controversial 1993 decision to deem secondhand smoke a human carcinogen.
The study found that, on average, a nonsmoking woman who has lived with a smoker at any time in her adult life faces a 30% increased risk of lung cancer. The research found a clear “dose-response” relationship, meaning the risk grew dramatically as exposure increased.
“This is a tremendously important paper,” said Stanton Glantz, a UC San Francisco researcher who has done extensive work on secondhand smoke. “The scientific evidence that passive smoking causes lung cancer is pretty ironclad. This makes the iron quite a lot thicker.”
The article comes at a time of intense debate over the dangers of secondhand smoke, also known as environmental tobacco smoke, or ETS. Nationwide, more than 600 state and local ordinances restrict smoking. Congress is considering a bill that would ban smoking in nearly every public building in the country.
The tobacco industry is waging a campaign to persuade Americans that secondhand smoke is less harmful than most people believe, and contends that government efforts to regulate it are not supported by science. Today’s JAMA article drew immediate criticism from the Tobacco Institute, the industry’s chief lobbying group.
The institute asserted that the study, “like 12 of the other 13 ETS studies conducted in the United States,” failed to show a statistically significant increase in risk. The group said the article “confirms the insubstantial and uncertain nature” of the dangers of secondhand smoke.
The lead author of the article, epidemiologist Elizabeth T.H. Fontham of Louisiana State University, countered: “The body of data available is not consistent with the Tobacco Institute’s contention.” After 40 years of denial that active smoking causes lung cancer, Fontham said, she did not expect the tobacco industry to acknowledge the risks of secondhand smoke.
Fontham and her colleagues, including epidemiologists at USC and UC Berkeley, tracked women in Atlanta, Houston, New Orleans, Los Angeles and San Francisco. Their research, a continuation of their work that was cited in last year’s EPA report, compared 653 nonsmoking women with lung cancer to a control group of 1,253 randomly selected women.
Unlike other secondhand smoke studies, which have focused primarily on women who were married to smokers and exposed in the home, the Fontham group also examined exposure in the workplace and social settings. The researchers used detailed questionnaires to determine when and where the women had been exposed, and for how many years.
The investigators found that women who had been exposed to secondhand smoke only during childhood did not face an increased risk of lung cancer. But women who were exposed during childhood and adulthood faced twice the risk of women exposed as adults only.
The research also demonstrated that workplace exposure may pose a greater risk than exposure at home. Women who had been exposed to secondhand smoke in the workplace for more than 30 years faced an 86% greater risk of lung cancer than women who had never been exposed at work, the study found. Women exposed for up to 15 years faced a 30% increase in risk, and women exposed for 16 to 30 years faced a 40% increase.
In the home, women exposed to more than 30 years of secondhand smoke faced a 23% increase in risk over those never exposed.
Glantz theorized that the reason for this is because smoking at work occurs in closer quarters than at home. But Fontham and her colleagues were unwilling to speculate on their results, and cautioned against interpreting the statistics to mean that exposure in the home is less risky.
“They are equally significant,” said Anna Wu, a USC epidemiologist who participated in the study. “This simply points out that exposure, whether it is at home or the workplace or in a social setting, if it is intense enough, it is going to be bad for you.”
The group also addressed some specific criticisms leveled by the tobacco industry against previous studies: that statistics have been culled from people who lied about their smoking habits, and that other risk factors--such as a high-fat diet--were responsible for lung cancer in nonsmokers.
Fontham said the researchers excluded 2% of the study participants after urine samples showed levels of cotinine--a nicotine byproduct--that were consistent with smoking. And, she said, the researchers adjusted their figures to account for participants’ eating habits.
Although the study looked only at women, the researchers said their findings hold for men as well. Most secondhand smoke studies have focused on women because women are more likely to be the nonsmoking partner.
The findings prompted the American Medical Assn. to call for further restrictions on smoking in public places, and for the U.S. Food and Drug Administration to regulate cigarettes as drugs because of the addictive nature of nicotine--a move the FDA is considering.
“Cigarettes are no different than syringes,” Dr. Randolph Smoak Jr., a member of the AMA’s board of trustees, told a Washington news conference at a joint appearance with Fontham. “They are a drug delivery device for nicotine. They should be regulated just as we regulate morphine and heroin.”
