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K E Y P O I N T S

Passive smoking is the act of breathing in secondhand smoke.

Tobacco smoke contains over 400 chemicals, and over 60 are known or suspected to be carcinogenic (cancer-causing).

A controversial study published in the British Medical Journal appears to show that in non-smokers regularly exposed to smoke via their spouses were not at significant risk of cancer or heart disease.

Despite the finding, the study has been strongly criticised, with a multitude of flaws highlighted.

Experts contend that the dangers of passive smoking are well documents and cite existing evidence from more than 50 studies.

According to Cancer Research UK, passive smokers are 20 to 30 per cent more likely to develop lung cancer than people not exposed to smoke, with several hundred deaths occurring as a direct result in the UK each year.

How dangerous is passive smoking?

Bupa investigative news - 27 May 2003
written by Rachel Newcombe, reporter for Bupa's Health Information Team

A new debate regarding the dangers of passive smoking has erupted following the publication of a study claiming that secondhand smoke might not be as harmful as previously believed. But, considering all the evidence already available concerning the dangers of passive smoking, should this research be taken seriously?

What were the headlines?

Coverage of the story appeared in all the major newspapers, with reports ranging from lengthy analysis, to short and brief mentions.

Among the many headlines were, "Claim that passive smoking does no harm ignites tobacco row", "Passive smoking may not damage your health after all, says research", "Passive smoking isn't such a peril, say researchers" and "Fury at 'smoke screen'".

What is the bigger picture?

The study appeared in the British Medical Journal (BMJ) and was based on research by James Enstrom, from the University of California, and Geoffrey Kabat, from the State University of New York. They analysed data from the American Cancer Society's (ACS) Cancer Prevention Study, which was started in 1959 and ended in 1998. In total 118,094 Californian adults had been studied, and Enstrom and Kabat focused on the 35,561 nonsmokers who were married to partners who smoked.

The researchers chose this subgroup of nonsmokers because they reasoned that being married to smokers meant that this group was exposed to secondhand smoke. According to their analysis of this group, passive smoking (by inhaling a spouse's cigarette smoke) wasn't significantly associated with an increased risk of death from coronary heart disease or lung cancer at any time or at any level of exposure. From this finding, the study's authors, suggest that passive smoking cannot cause the 30 per cent increased risk of coronary heart disease that it is currently believed to cause. Instead, they argue that it might cause a much smaller effect. However, they couldn't rule out the possibility of a 20 per cent increased risk of lung cancer and chronic obstructive pulmonary disease.

But the American Cancer Society (ACS) - the organisation whose data was used - has strongly criticised the study. The analysis was funded by the tobacco industry and supported by the now defunct Centre for Indoor Air Research (CIAR) - a group funded and founded by cigarette companies. "We are appalled that the tobacco industry has succeeded in giving visibility to a study with so many problems it literally failed to get a government grant," said Dr. Michael J. Thun, vice president of epidemiology and surveillance research. "The ACS welcomes thoughtful, independent peer review of our data, but this study is neither reliable nor independent."

The data for the 35,561 nonsmokers who were married to smokers was obtained from the ACS Cancer Prevention Study I (CPS-I). The ACS was aware of Dr. Enstrom's work and is said to have repeatedly advised him that using the data to "study the effects of secondhand smoke would lead to unreliable results". The society points out that the analysis was based on only a tiny subset - 10 per cent - of the CPS-I data and that it was scientifically flawed in a number of ways.

The most serious design flaw, the society argues, is that there's an inability to distinguish people who were exposed to secondhand smoke from those who weren't. This is because:

Participants were enrolled in 1959, when exposure to secondhand smoke was so pervasive that virtually everyone came into contact with it, whether they were married to a smoker or not.
No information was collected on the sources of secondhand smoke other than spousal smoking.
No information on smoking habits after 1972 was included in the analysis, even though the observation period continued for another 26 years.
On average, participants were 52 years old when enrolled on the study. Many spouses who reported smoking in 1959 would have died, quit smoking or ended the marriage during the 38-year follow up, yet their surviving partners are still classified being passive smokers in the analysis.
Much of the follow up relates to older age groups where the effects of many environmental risk factors become less apparent.

More than 50 studies on the health impacts of passive smoking have been carried out over the past 25 years, including a number of landmark studies providing significant evidence of passive smoking risks. Such work includes research by the International Agency for Research on Cancer (IARC), the Scientific Committee on Tobacco and Health and the ACS.

Notable research includes a study published in the BMJ in 1997, conducted by Hackshaw and colleagues, which analysed 37 passive smoking studies and found a 24 per cent increase in lung cancer among people living with smokers. In fact, said the charity Action on Smoking and Health (ASH), "Tobacco specific carcinogens found in the blood of non-smokers provided clear evidence of the effect of passive smoking."

Additionally, far more reliable data was obtained in the ACS Cancer Prevention Study II (CPS-II) study, which was about 10 times larger than Dr. Enstrom's work. They enrolled patients in the 1980s, when fewer exposures to tobacco smoke outside the home existed, and therefore far less "background noise", and follow-up has been much better (over 99 per cent). The results unquestionably show an increased risk of lung cancer and heart disease.

“Science is all about weighing the balance of probabilities, and in this case the evidence that passive smoking is dangerous still overwhelms that which says that it is not harmful. If this had been a well-designed, well-conducted study we should all have had to reconsider the situation, but it doesn't actually look as if we need to.”

Dr Virginia Warren,
assistant medical director
Bupa Group

What does this mean?

The paper has received numerous criticisms, including from the British Medical Association (BMA). Like ACS, they believe it is scientifically flawed, especially as the data had been around for decades, and was "judged by many expert groups to be inadequate to accurately measure passive smoking."

Dr. Vivienne Nathanson, head of science and ethics at the BMA, said, "It would be wrong to be swayed by one flawed study funded by the tobacco industry - set against the studies and numerous expert reviews that demonstrate that passive smoking kills."

Dr. Ian Campbell, president of the British Thoracic Society (BTS), said, "This is yet another piece of evidence in the difficult debate on the effects of passive smoking. We believe that passive smoking has a much weaker effect on the lungs than actual smoking, but there are real risks involved, which need to be addressed."

He added that, "Medical evidence has conclusively shown that passive smoking has a detrimental effect on children's lungs and there is also good evidence that suggests that passive smoking worsens the effects of asthma. Further research into the effects of passive smoking on lung health are needed and should be encouraged by governmental and other funding agencies."

Not surprisingly, tobacco companies are using the findings to argue against a ban on public smoking. Tim Lord, chief executive of the Tobacco Manufacturers' Association, commented, "This appears to be a large and very important study. As is clear from the BMJ's own editorial, the debate on environmental tobacco smoke is far from over, contrary to what many people say."

He added that, although the needs of non-smokers should be met in public places, "the scientific evidence does not justify total bans on smoking in the workplace or other public places." British American Tobacco Company made similar comments, and said, "The study illustrates that calls for bans on public smoking cannot be justified."

A C T I O N P O I N T S

If your spouse smokes, encourage him/her to smoke outside.

If you smoke, avoid smoking around babies or children.

If you smoke, be thoughtful with your smoking habits when around non-smokers.

Consider giving up smoking - the health benefits are numerous for you, as well as those close to you.

What does this mean to me?

Dr. Harmon J. Eyre, national chief medical officer at ACS, said it's important to keep the study in perspective, and remember the wealth of information already available. "CPS-II [the positive study] is one of more than 50 studies now published that have shown non-smokers married to smokers have an increased risk of lung cancer," he said.

What's more, unlike the Enstrom work, "These studies have been scrutinised by multiple independent consensus committees, all of which certify their credibility. Most recently, the IARC reviewed the evidence and concluded secondhand or environmental tobacco smoke is carcinogenic to humans," he added.

As Dr. Vivienne Nathanson stressed, "There is overwhelming evidence, built up over decades, that passive smoking causes lung cancer and heart disease, as well as triggering asthma attacks. In children, passive smoking increases the risk of pneumonia, bronchitis, and reduces lung growth, as well as both causing and worsening asthma."

With this in mind, the advice from all organisations remains the same - that regular exposure to passive smoke is harmful and should be avoided if possible. As well as causing lung cancer, it can trigger miscarriages and premature births, and is very harmful for babies and children, with links to cot death, asthma and other respiratory problems.

Although it's tricky to avoid tobacco smoke in public areas, ASH recommends sitting in non-smoking areas of restaurants and they are hopeful that legislation to ban smoking in workplaces will eventually be implemented.

Summary

Despite this study that seems to show that passive smoking isn't harmful, experts are not convinced. They say there's overwhelming evidence that shows that secondhand smoke is dangerous and they recommend that non-smokers limit their exposure to it as much as possible.