Studies of dietary factors have yielded intriguing findings, but the fact that the diets of smokers tend to be less healthy than those of nonsmokers makes it challenging to separate the influence of dietary factors from the effects of smoking. When considering the relationships between lung cancer and dietary factors, confounding factors related to cigarette smoking cannot be dismissed as a possible explanation.
A meta-analysis of leisure-time physical activity and lung cancer risk revealed that higher levels of physical activity protect against lung cancer. The overall evidence for physical activity has been mixed, but several studies have reported that individuals who are more physically active have a lower risk of lung cancer than those who are more sedentary,[40,41,42] even after adjustment for cigarette smoking. The World Cancer Research Fund evidence review rated the inverse association between physical activity and lung cancer as "limited suggestive" evidence.
Studies of physical activity yield findings consistent with an inverse association, but the fact that physical activity behaviors differ between smokers and nonsmokers makes it difficult to infer that there is a direct relationship between physical activity and lung cancer risk.
Interventions Associated With Decreased Risk of Lung Cancer
Smoking avoidance and cessation
Substantial harm to public health accrues from addiction to cigarette smoking. Compared with nonsmokers, smokers experience a dose-dependent increase in the risk of developing lung cancer (and many other malignancies).[43,44]
Approximately 85% of all lung cancer deaths are estimated to be attributed to cigarette smoking. Substantial benefits accrue to the smoker by quitting smoking. (Refer to the PDQ summary on Cigarette Smoking: Health Risks and How to Quit for more information.) Avoidance of tobacco use is the most effective measure to prevent lung cancer. The preventive effect of smoking cessation depends on the duration and intensity of prior smoking and upon time since cessation. Compared with persistent smokers, a 30% to 50% reduction in lung cancer mortality risk has been noted after 10 years of cessation.[11,44,45,46]
The benefits of tobacco control at the population level provide strong quasi-experimental evidence that reducing population-level exposure to cigarettes has resulted in population-level declines in the occurrence of lung cancer. Reduced tobacco consumption, due to both decreases in smoking initiation and increases in smoking cessation, led to a decline in overall age-adjusted lung cancer mortality among men since the mid-1980s, consistent with reductions in smoking prevalence among men since the 1960s. Gender differences in time trends for lung cancer are a reflection of (1) the later adoption of cigarette smoking in women compared with men and (2) the later reduction in smoking prevalence among women compared with men.
Smoking cessation guidelines
Nicotine dependence exposes smokers in a dose-dependent fashion to carcinogenic and genotoxic elements that cause lung cancer. Overcoming nicotine dependence is often extremely difficult. The Agency for Healthcare Research and Quality (formerly the Agency for Health Care Policy and Research [AHCPR]) developed a set of clinical smoking-cessation guidelines for helping nicotine-dependent patients and health care providers. The six major elements of the guidelines include the following:
- Clinicians must document the tobacco-use status of every patient.
- Every patient using tobacco should be offered one or more of the effective smoking cessation treatments that are available.
- Every patient using tobacco should be provided with at least one of the effective brief cessation interventions that are available.
- More intense interventions are more effective than less intense interventions in producing long-term tobacco abstinence, reflecting the dose-response relationship between the intervention and its outcome.
- One or more of the three treatment elements identified as being particularly effective should be included in smoking-cessation treatment:
- Nicotine-replacement (e.g., nicotine patches and gum) or other evidence-based smoking cessation pharmacotherapy (e.g., varenicline or bupropion).
- Social support from clinician in the form of encouragement and assistance.
- Skills training/problem solving (cessation/abstinence techniques).
- To be effective, health care systems must make institutional changes resulting in systematic identification of tobacco users and intervention with these patients at every visit.