VicHealth Centre for Tobacco Control
Compelling evidence that cigarette smoking is the principal cause of lung cancer has existed since the 1930s and has been widely disseminated in the English-speaking world since 1950, when several major epidemiological studies of smoking and lung cancer were published in the United Kingdom and the United States1. Between 1950 and the mid-1990s, the tobacco industry responded to the ever-increasing body of evidence demonstrating the harm caused by cigarette smoking by steadfastly maintaining that there was no proven causal connection between smoking and any disease. However, as a form of insurance against the failure of the “no proof” argument, tobacco industry spokespeople have long suggested that efforts are being made to produce a “safe” cigarette or, at least, a “safer” one. Knowing that many smokers were unwilling or unable to quit, public health experts have long sought to encourage or coerce the tobacco industry to produce “safer” cigarettes. I will describe current developments regarding “safer” cigarettes later in this article. But first, I will review the “low-tar” program to reduce smoking-related harm, which has been a spectacular failure in public health terms but remains largely intact. Knowing how and why the low-tar program failed helps us to better understand what will be required of a new harm-reduction program that has a reasonable chance of succeeding.
In the late 1960s, low-tar cigarettes were embraced by public health experts as a potentially useful means of reducing disease and mortality among those smokers who were unwilling or unable to quit2,3. The initial reasoning behind the low-tar program was that because, firstly, lung cancer risks increased with more cigarettes per day and more years of smoking and, secondly, tar-painting experiments on mice showed strong dose-response relationships, cigarettes that delivered lower doses of tar to smokers would mean less disease4. Later on, when it became clearer that nicotine was addictive, it was also believed that low-tar smokers would have reduced intakes of nicotine, thus facilitating future quitting. Fortunately for the tobacco industry, but unfortunately for everyone else, many smokers decided to switch to low-tar brands and reduce their smoking-related risks, rather than attempt to eliminate them through quitting. What was even more unfortunate for smokers who down-switched was that few would have experienced any real reduction in harmful intakes. Rather, down-switchers merely gained a compelling illusion of reduced risk, through reassuring but misleading numbers printed on the side of cigarette packs and reassuring but misleading sensations of mildness.
The low-tar program had two fatal flaws:
1. Low-tar cigarettes, as identified by the standard smoking machine yield test (which involves 35ml puffs, over two seconds, once per minute), could potentially deliver far more tar and nicotine to smokers than the yield figures suggested. Over time, this problem got worse, as low-tar cigarettes were re-engineered to have increased elasticity or consumer demand responsiveness5.
2. Most smokers regulate their intakes with relative precision in order to gain rewarding sensations and avoid withdrawal7. Consequently, they respond to lower-tar cigarettes by smoking them more intensively in order to gain target nicotine doses. If smokers cannot obtain their target nicotine doses from particular brands, they will generally simply reject those brands.
In short, low-tar cigarettes simply did not provide enough resistance to smokers’ unconscious efforts to achieve constant nicotine intakes. This was no accident.
Perhaps the most crucial tobacco industry innovation in developing low-tar cigarettes capable of delivering nicotine doses that would satisfy addicted smokers was filter ventilation. This is the perforation of the filter tipping paper with barely visible or invisible holes between 11mm and 18mm from the end of the cigarette. When a filter vented cigarette is machine smoked a pre-set proportion of each puff consists of fresh air drawn through the vents. This innovation has enabled commercially viable brands in Australia with standard machine-tested tar yields of 1mg and nicotine yields of 0.1mg (figures that invite belief in virtual safety, when compared to regular cigarettes with tar yields of 12-16mg and nicotine yields of 1-1.3mg)5.
However, as noted above, addicted smokers do not smoke like machines – they unconsciously seek constant intakes of nicotine, rather than constant puff volumes. Consequently, they learn to overcome yield reduction mechanisms. Low-tar smokers block filter vents with their fingers and lips to make the smoke more concentrated. They also take larger and faster puffs, which function to reduce ventilation levels, even in the absence of any vent blocking8.
Most low-tar smokers are likely to be gaining very similar intakes of nicotine, carcinogens and other toxins to those they would gain from a regular cigarette, but they gain these intakes in larger volumes of more dilute smoke. Because the smoke is more dilute, it is generally milder in taste and less irritating. This provides a powerful source of belief for low-tar smokers that they are indeed smoking less harmful products9. A recent survey found that a majority of self-reported ‘lights’ smokers in Australia continue to believe they get some relative health benefit, despite efforts by health authorities and the media to convey messages to the contrary10.
Proposals to remove standard tar, nicotine and carbon monoxide yields from cigarette packs and proposals to ban the use of ‘light’ and ‘mild’ brand descriptors are currently under consideration by the Australian Government. However, given the high degree to which smokers’ sensations influence their beliefs about the harmfulness of the cigarettes they are smoking, there are serious questions about whether enactment of these proposals will be adequate to finally dispose of the low-tar program for safer cigarettes. Cigarettes with filter ventilation are arguably inherently deceptive, rather than simply deceptive in the context of light and mild brand descriptors and standard tar, nicotine and carbon monoxide yield labelling. If the existing variety of products continues to be available, but is merely identified through less explicit means of brand differentiation such as having six different pack colours for each brand family, many smokers will continue to believe they are making a safer choice by smoking one of the more heavily ventilated varieties.
The fact that most smokers were preserving their tar and nicotine intakes during the period when machine-tested tar and nicotine yields were declining spectacularly was not the only thing that went seriously wrong with the low-tar program. In so far as tar yields were treated as the main index of potential harm, they were also misleading at another level. This is because exposures to some important carcinogens contained in cigarette smoke appear to have increased over the past three to four decades11.
In the 1960s, a group of substances called polynuclear aromatic hydrocarbons (or PAHs) formed the focus of attention as potential carcinogens in tobacco smoke12. PAHs had long been suspected carcinogens and tar painting experiments on mouse skin showed PAH-rich tar fractions to be the most carcinogenic. Accordingly, PAHs became targets for selective reduction in cigarette smoke. One proposal for reducing PAHs was to increase the nitrate content of tobacco12. Subsequent actions by the tobacco industry, such as using tobacco grown with heavier application of fertilisers and using more tobacco stem in blending, had exactly this effect. Increasing nitrogen content also had the effect of reducing machine-tested tar yields, which was also useful for the tobacco industry’s purposes of appearing to provide safer cigarettes. However, the pitfall of this means of producing a supposedly safer cigarette was that the very steps that were likely to reduce PAH levels in cigarette smoke were likely to increase the levels of another group of powerful carcinogens, the tobacco-specific nitrosamines (TSNAs).
TSNAs are produced from nicotine and related tobacco alkaloids during curing and combustion, especially in nitrogen-rich conditions13. Little was known about TSNAs before the 1970s and TSNA-rich tar fractions did not appear to be particularly carcinogenic when applied to mouse skin14. However, other tests of biological activity show TSNAs to be strongly carcinogenic. TSNA exposures also appear to be strongly related to pulmonary adenocarcinoma, a form of lung cancer that has become relatively more prevalent in recent years11.
Furthermore, there is evidence from the UK and US that the lifetime risks of cigarette smoking increased between the 1960s and the 1980s, particularly lung cancer risks15. These findings persist after controlling for number of cigarettes per day and duration of smoking. Thus, they are consistent with increased exposures to carcinogens during the period of the low-tar program and TSNAs are the primary candidate agents.
The tobacco industry now claims to be taking TSNA exposures very seriously and taking appropriate steps, such as re-engineering curing barns and selecting tobacco crops, to ensure that TSNA deliveries are reduced13. If TSNA deliveries can be reduced without increasing PAH deliveries or deliveries of other carcinogens and respiratory/cardiovascular toxins to such an extent that it constitutes a zero-sum game, it would be reasonable to expect that cigarettes would become at least marginally less dangerous. However, the tobacco control community will need to take extreme care that future regulation of specific smoke emissions does not produce a situation where the tobacco industry can meet regulatory limits by allowing dangerous emissions that slip through the regulatory net to increase, thus undermining the anticipated benefits.
It would also be reasonable to expect that selection of tobacco crops grown on soils with low burdens of heavy metals, treated with fertilisers with similarly low heavy metal burdens, could contribute to somewhat less harmful cigarettes16. In this case, there is a real danger that use of this strategy could result in shifting of risks from the developed world to the developing world, through dumping of the dirtiest tobacco on the poorest countries with the least power to resist. This would compound the public health disaster that is resulting from the multinational tobacco companies’ successes in building developing world markets. Likewise, dumping of high TSNA tobacco on poor countries would constitute an unacceptable form of risk shifting17.
Finally, it is plausible that some of the innovations employed in specific brands marketed as potential reduced exposure products in the US could play some role in making all commercially available cigarettes somewhat less harmful if they were in general use. For instance, Omni, produced by Vector Tobacco, employs a palladium catalyst to increase combustion (as well as having reduced TSNA tobacco) and it is plausible that this innovation could reduce harmful deliveries. A recent short-term forced switching study18found that subjects’ levels of TSNA and PAH biomarkers were reduced somewhat during the period they smoked Omni (although the reductions in the PAH biomarker levels did not achieve statistical significance). However, the study also found that subjects’ intake reductions were much lower than is suggested in promotional material for Omni. That provides cause for concern. If a new generation of so-called safer cigarettes can produce modest reductions in harmful intakes, but smokers are somehow convinced that they can achieve substantial reductions in risk, the likely adverse effects on quitting and uptake rates will far outweigh the limited benefits for those smokers who are never going to quit.
In conclusion, less harmful cigarettes remain a theoretical possibility but there are substantial obstacles to attaining them in practice. Overcoming these obstacles will necessarily involve governments being willing to regulate the tobacco industry. They must also be willing to provide the necessary resources for adequate surveillance, so those developments serving the interest of public health can proceed and those which do not are brought to a halt.
1. Proctor RN. “Tobacco and Health” – Expert witness report filed on behalf of plaintiffs in “The United States of America, Plaintiff, v. Philip Morris, Inc, et. al. Defendants” Civil Action No.99-CV-02496 (GK) (Federal Case). The Journal of Philosophy, Science and Law. [serial on the Internet]. 2004 March 31;4: Available from: www.psljournal.com/archives/papers/tobacco.cfm.
6. Benowitz NL. Compensatory smoking of low yield cigarettes. In: U.S. Department of Health and Human Services. Risks associated with smoking cigarettes with low machines measured yield of tar and nicotine. Bethesda, MD: U.S. Department Of Health And Human Services, Public Health Service, National Institutes of Health, National Cancer Institute, 2001:39-63.
8. Kozlowski LT, O’Connor RJ, Sweeney CT. Cigarette design. In: U.S. Department of Health and Human Services. Risks associated with smoking cigarettes with low machines measured yield of tar and nicotine. Bethesda, MD: U.S. Department of Health And Human Services, Public Health Service, National Institutes of Health, National Cancer Institute, 2001;13-37.
10. Borland R, Yong H-H, King B, Cummings M, Fong GT, Elton TE, Hammond D McNeill A. Use of and beliefs about ‘light’ cigarettes in four countries: Findings from the International Tobacco Control Policy Evaluation Survey. Unpublished manuscript, Melbourne: VicHealth Centre for Tobacco Control, 2004.
11. Hoffman D. The changing cigarette: chemical studies and bioassays. In: U.S. Department of Health and Human Services. Risks associated with smoking cigarettes with low machines measured yield of tar and nicotine. Bethesda, MD: U.S. Department of Health And Human Services, Public Health Service, National Institutes of Health, National Cancer Institute; 2001:59-91.
14. Hoffman D, Djordjevic MV, Brunnemann KD. Changes in cigarette design and composition over time and how they influence the yields of smoke constituents In: The FTC cigarette test method for determining tar, nicotine and carbon monoxide yields of U.S. cigarettes. Bethesda, MD: National Institutes of Health; 1996. 15-37.
15. Burns DM, Major JM, Shanks TG, Thun MJ. Smoking lower yield cigarettes and disease risks. In: U.S. Department of Health and Human Services. Risks associated with smoking cigarettes with low machines measured yield of tar and nicotine. Bethesda, MD: U.S. Department Of Health And Human Services, Public Health Service, National Institutes of Health, National Cancer Institute, 2001; 65-158.
18. Hatsukami DK, Lemmonds C, Zhang Y, Murphy SE, Le C, Carmella SG, Hecht SS. Evaluation of carcinogen exposure in people who used “reduced exposure” tobacco products. J Natl Can Inst 2004 Jun 2;96(11):844-52.