The composition of cigarette smoke has altered over the past 40 years, mostly due to manufacturing changes. Filter tips, which became popular during the 1950s and 1960s, have reduced tar and nicotine content. New manufacturing techniques have helped reduce tar, nicotine and carbon monoxide content further.(140) Tobacco scientists have also sought and developed crop varieties rendering lower tar yields.(141,142)
The 1981 report of the US Surgeon General, 'The Changing Cigarette', reviewed the evidence about the health effects of smoking lower tar cigarettes.(143)
The principal findings of the report were as follows:
1. There is no safe cigarette and no safe level of consumption.
2. Smoking cigarettes with lower yields of 'tar' and nicotine reduces the risk of lung cancer and, to some extent, improves the smoker's chance for longer life, provided there is no compensatory increase in the amount smoked. However, the benefits are minimal in comparison with giving up cigarettes entirely. The single most effective way to reduce hazards of smoking continues to be that of quitting entirely.
3. It is not clear what reductions in risk may occur in the case of diseases other than lung cancer. The evidence in the case of cardiovascular disease is too limited to warrant a conclusion, nor is there enough information on which to base a judgement in the case of chronic obstructive lung disease. In the case of smoking's effects on the foetus and newborn, there is no evidence that changing to a lower 'tar' and nicotine cigarette has any effect at all on reducing risk.
4. Carbon monoxide has been impugned as a harmful constituent of cigarette smoke. There is no evidence available, however, that permits a determination of changes in the risk of disease due to variations in carbon monoxide levels.
5. Smokers may increase the number of cigarettes they smoke and inhale more deeply when they switch to lower yield cigarettes. Compensatory behaviour may negate any advantage of the lower yield product or even increase the health risk.
6. The 'tar' and nicotine yields obtained by present testing methods do not correspond to the dosages that the individual smokers receive: in some cases they may seriously underestimate these dosages.
7. A final question is unresolved, whether the new cigarettes being produced today introduce new risks through their design, filtering mechanisms, tobacco ingredients, or additives. The chief concern is additives. The Public Health Service has been unable to assess the relative risks of cigarette additives because information was not available from manufacturers as to what these additives are.
Sir Richard Doll has said that smoking lower tar cigarettes is not likely to reduce cancer risk for sites other than lung, larynx, oesophagus and mouth(144):
... for low tar cigarettes are also low in nicotine and the smoke from them is inhaled more deeply, so that the same level of nicotine is attained in the blood. The deep inhalation also results in the aerosol droplets that carry the tar increasing in size in the warm and moist air and precipitating in the alveoli. The bronchi may, therefore, be spared, while the greater proportional absorption in the alveoli may result in the same total amount of carcinogens reaching the blood and being carried to distant organs, even though the absolute amount of carcinogens is reduced.
See Chapter 5, Section 8 for discussion about additives in Australian cigarettes.
It is possible that potential quitters have elected to switch to low tar cigarettes rather than quit entirely, the option of changing down being dramatically easier for the addicted smoker. In combination, compensatory smoking and the adoption of low tar brands rather than complete cessation, may have in fact have brought about more smoking, and hence more morbidity and mortality, than would have occurred in their absence.(142) It has also been suggested that low tar cigarettes may be a factor in recruiting girls and young women to smoke in larger numbers, their milder taste making initiation easier.(145)
Despite the shortcomings of lower tar cigarettes, they may bring some benefit to public health if:
ð the yields of other harmful components (nicotine, carbon monoxide and other agents) are reduced, as well as tar;
ð the public is made aware that compensatory inhalation may occur, and should be avoided;
ð the public is made aware that the benefits of smoking lower yield cigarettes can only be small compared with those of avoiding smoking altogether;
ð the public is made aware that smoking of low tar cigarettes only appears to affect some disease outcomes;
ð low tar brands are not promoted as the answer to the ill health caused by tobacco smoking, but as one facet of a general strategy to reduce tobacco caused disease in a community in which some will choose to smoke regardless of the health consequences.(146)
It is important to note that any health benefits so far attributed to lower tar cigarettes have been observed from studies involving smokers changing from cigarettes containing by today's standards, very high tar yields (for example 35 milligrams). Modern low tar cigarettes contain as little as 1 mg of tar, and all Australian made cigarettes currently on the market yield 14 mg of tar or less. Since cigarettes containing these lower levels of tar have not been available long enough for impact on disease levels to have been assessed (the risk of developing lung cancer depending on the smoking history 15-20 years earlier), one cannot say whether these more recent reductions in yield will further reduce the risk of lung cancer.(140) In any case, where compensatory smoking takes place, any risk reduction is compromised. The most substantial benefit to health is gained by stopping altogether.(140)
Refer to Chapter 5 for full discussion of tar, nicotine and carbon monoxide levels in Australian cigarettes.