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Sci Tech
Passive smoking controversy
RECENTLY, THE British Medical Journal lowered its guard and published a paper titled `Environmental tobacco smoke and tobacco related mortality in a prospective study of Californians 1960-1998' by Enstrom & Kabat.
Tabloid style, the journal's cover page carried a provocative title `Passive Smoking may not kill'. This dismayed many readers. They felt that the journal did it for cheap publicity. The news got wide coverage in print and electronic media. The journal received an avalanche of over 50 electronic responses in three days. Most of them are crying hoarse on the role of the journal in publishing a `fatally flawed study'. The spat continues.
The accompanying BMJ editorial included the word `controversy'. To many, there was no controversy. An overwhelming body of scientific evidence has proven the health impact of passive smoking.
A reader claimed that there are over 50 published studies that confirm the increased risk of lung cancer and heart disease for non-smokers married to smokers.
Enstrom and Kabat analysed the Californian sub-sample of the American Cancer Society's (ACS) first cancer prevention study. The sample of 35561 never smokers who had a spouse with known smoking habits is extracted from a larger set of 1,18,094 adults enrolled in the ACS study in late 1959.
The study does not support a causal relation between environmental tobacco smoke and tobacco related mortality although it does not rule out a small effect. The authors conclude that the association between exposure to environmental tobacco and coronary heart disease and lung cancer may be considerably weaker than generally believed.
Studies of this type have infirmities. Smoking habits may be quantified, but how do we quantify non-smoker's exposure? A reader asserted that it would be impossible to find true negative control subjects for passive smoking studies.
Jayant Vaidya of University of London noted that the study assumed that there is considerable difference between exposures to Environmental Tobacco Smoke (ETS) of never smoker's spouse compared to ever smoker's spouse.
Never smoker's spouse would have been exposed to considerable ETS before late 1990s when the general exposure to ETS in California started declining. Only in the last 3-4 years of the 39-year study when the ETS exposure at work place might have been so reduced that there might be a difference in the two groups.
Vaidya pointed out that in spite of the large size of the study, it would be difficult to demonstrate the difference of a small percentage in mortality between the two groups. Many readers agreed.
Dr.Michael Thun, Vice President, Epidemiology and Surveillance Research, American Cancer Society (ACS), stated that ACS does not endorse or agree with the study. ``Scientifically, the fatal flaw of the paper is that the information collected on ETS is insufficient to distinguish persons who were exposed from those who were not.
When the study began in 1959, no information was collected on potential ETS exposure." He revealed the fact that Dr.Enstrom continued his analysis of ETS exposure despite repeated cautions from Dr.Thun and other ACS epidemiologists that his long term follow up of Californian subset of Cancer Prevention Study -I (CPS-I) would not be informative about this issue. Many other critics agreed.
The timing of the article shocked a few. The article got published a few days before the opening of the World Health Assembly, which adopted the Framework Convention for Tobacco Control. Ironically, an article in the convention asserted thus: ``Parties recognize that scientific evidence has unequivocally established that exposure to tobacco smoke causes death, disease and disability." Quoting this article a reader concluded that if BMJ had decided to side with the tobacco industry in what it still considers a `controversy', it could not have chosen a better move and a better time.
Professor Martin McKee, editor of the European Journal of Public Health did some diligent literature search to expose the conflict of interest of Dr.Enstrom.
``A level of trust has to be developed based on my past research on passive smoking... A substantial research commitment from your part is necessary in order for me to effectively compete against the large mountain of epidemiologic data and opinions that already exist regarding the health effects of ETS and passive smoking'' These extracts from Enstrom's letter of January 15, 1997 to tobacco industry officials soliciting support for his research are too damning to be ignored. The article and the responses highlighted the conflicts of interests of both pro and anti tobacco lobby.
It took four decades of study by Richard Doll, an eminent epidemiologist at the Imperial Cancer Research Fund Cancer Studies Unit at Oxford to declare thus; ``It now seems that about half of all cigarette smokers will eventually be killed by their habit." Active controversy on passive smoking may dilute the impact of Doll's message.
K.S.Parthasarathy
Secretary
Atomic Energy Regulatory Board Mumbai
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