May 15, 2003 -- A controversial new study that questions the health risks of being exposed to secondhand smoke -- a factor often said to contribute to some 50,000 American deaths each year -- has outraged some health officials.
The new study, to be published in the May 17 issue of the British Medical Journal, shows no measurable rates of heart disease or lung cancer among nonsmokers who ever lived with smokers, and reports only a slight increased risk of chronic obstructive pulmonary disease. Many health agencies, including the U.S. Surgeon General's Office, have long said that secondhand smoke boosts the risk of heart disease by about 30% and lung cancer risk by 25% in nonsmokers.
"We found no measurable effect from being exposed to secondhand smoke and an increased risk of heart disease or lung cancer in nonsmokers -- not at any time or at any level," lead researcher James Enstrom, PhD, MPH, of the UCLA School of Public Health, tells WebMD. "The only thing we did find, which was not reported in the study, is that nonsmokers who live with smokers have a increased risk of widowhood because their smoking spouses do die prematurely."
However, the American Cancer Society blasted the study -- and Enstrom -- for misusing its own data in an attempt to "confuse the public about the dangers of secondhand smoke." And former U.S. Surgeon General Julius Richmond, MD, is expected to join other medical experts in calling the study "bogus" in a news conference on Friday.
The study was funded in part by the Center for Indoor Air Research, which the American Cancer Society says is an arm of Philip Morris and other tobacco companies. Enstrom requested and received funding for the study in 1997.
For his finding, Enstrom used data from an ACS study -- the Cancer Prevention Study I that began in 1959 as one of the first major smoking studies. It involved some 1 million Americans across the country; Enstrom focused on some 36,000 nonsmoking Californians whose spouses had smoked, part of the 118,000 state residents in the trial. Although the study ended in 1972, Enstrom traced the cause of death of some 7,000 of those participants until 1998.
"ACS scientists and in particular, myself, had repeatedly asked him not to use the data to study the effects of secondhand smoke because it would lead to unreliable results," Michael Thun, MD, head of epidemiological research for the ACS, tells WebMD. "And it did."
Thun says the study, co-authored by Geoffrey Kabat, PhD, of the State University of New York at Stony Brook, is flawed for several reasons:
- There's no information on smoking habits after 1972, even though the observation period went another 26 years. "We don't know if the nonsmokers continued to be exposed to secondhand smoke, or if their spouses continued to smoke," Thun tells WebMD.
- Since the participants were an average of age 52 when the study began in 1959, many smoking spouses could have died, quit smoking, or ended the marriage before 1972, when Enstrom started his observation phase. This would have affected the secondhand smoke exposure of the nonsmokers. In addition, environmental factors such as secondhand smoke are less apparent in older ages.
- Participants were first enrolled in 1959, when secondhand smoke was pervasive. "Most people were exposed to it, pretty much everywhere, whether or not they were married to smokers."
- The finding is based on only 10% of the original study participants.
- The tobacco industry funded the study as part of an ongoing campaign to publish studies that question the dangers of secondhand smoke. "It views secondhand smoke as one of the most dangerous components against it, since it's what causes cities and states to restrict public smoking," says Thun. "And it actively seeks out this kind of research to confuse the public."
In fact, researchers reported in the Journal of the American Medical Association in 1998 that 75% of studies done between 1980 and 1995 that found no link between secondhand smoke and health problems were funded by tobacco companies. In that review, researchers examined 106 studies conducted in those 15 years; two in three indicated secondhand smoke does contribute to lung and heart disease.
"While this study is flawed, there are at least 50 very reputable studies that find a link between secondhand smoke and lung cancer and at least 50 others that find an increased risk of heart disease," says Thun.
Among them: Two findings from the newer Cancer Prevention Study II that began in the 1980s -- the follow-up to the study used for Enstrom's research -- that suggest nonsmokers face a 20% increased risk for both heart disease and lung cancer when exposed to secondhand smoke. "The consensus of multiple health committees from around the world, including the surgeon general, is that secondhand smoke is definitely related to lung cancer and heart disease, and may be also be related to chronic lung disease."