Harm Reduction in a Persistent Smoker

By David J. Riley, MD, FCCP

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Commentary on Tobacco Harm Reduction

Reducing Smoking Without Quitting

Evidence suggests that the amount smoked is related to the risk of tobacco-related diseases. This provides supportive evidence for encouraging reduced smoking without actually quitting. Several epidemiologic studies have shown a dose-response relationship between cigarette exposure and the risk of myocardial infarction, COPD, lung cancer, and stroke (reviewed in the IOM report¹). Investigators have made estimates of the effect of reducing smoking on lung cancer. One case-control study reported a 20% reduction in risk of lung cancer in a group who decreased daily consumption by > 25% compared with those who continued to smoke, but this was not significant.² Another study reported that reducing cigarette consumption by 50% reduced the risk of lung cancer by 16%, a barely significant change.³ Other studies showed that smokers who switched to cigars or pipes had a lower risk than those who continued to smoke cigarettes.⁴ Limitations of these studies include recall bias and lack of independent measurements to validate self-reported smoking.

A large survey conducted by the American Cancer Society⁵ suggested that a dose-response relationship exists between mortality from COPD and number of cigarettes smoked per day. It was estimated that if smoking 24 cigarettes per day is reduced by half, measurable reductions in morbidity and mortality from COPD may result. It has been shown that an aggressive approach to reduce smoking by combining nicotine replacement products, bupropion sustained release (SR), and counseling can result in a quit rate of 30% over a 2-year period.⁶ Other studies suggest that most smokers can reduce the number of cigarettes smoked per day to 8 to 10 cigarettes without having major withdrawal symptoms.⁷ It is conceivable, therefore, that some smokers who smoke 24 cigarettes per day might be able to cut this rate in half with pharmaceutical products and counseling.

Taken together, these dose-response studies appear to justify a harm-reduction strategy if validated by future population studies. However, the assumption of a simple relationship between dose and response is likely oversimplified. The curves relating smoking and death rates are curvilinear, indicating that reduced cigarette consumption may benefit light smokers more than heavy smokers. It should be remembered that there is no evidence of a safe threshold below which the risk of smoking is negligible.

Other observations suggest that reducing the amount smoked leads to less decline in lung function. Three studies have measured the effect of reduced smoking (consumption reduced by at least 25%) over a 1-year period. In one study, tests of small airway function improved 1 year after reduced smoking,⁸ and a second study showed that FEV₁ improved.⁹ A third study examined the change in FEV₁ over a 5-year period in subjects who were able to reduce smoking from > 15 cigarettes per day to < 15 cigarettes per day.¹⁰ Regression analysis showed that smoking reduction resulted in a benefit in subjects younger than 55 years of age but not in older subjects. There are important limitations of study design in all three studies, as none were primarily designed to test whether reduced smoking leads to a slower rate of loss of lung function. Prospective studies are needed to extend these studies and examine whether reducing smoking can abate loss of pulmonary function.

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