Lowering Lung Cancer Risk with Exercise
ABSTRACT & COMMENTARY
Synopsis: Among 81,000 smokers, risk of lung cancer decreased with increasing leisure-time physical activity.
Source: Thune I, Lund E. Int J Cancer 1997;70:57-62.
Smoking is the dominant risk factor for the development of lung cancer. However, nicotine addiction is not easy to break. Even though we recommend that people stop smoking, only a minority of smokers who try to stop smoking are successful. Other risk-modifying behaviors would be of interest.
Thune and Lund, in a study involving men and women in Norway, have previously reported that physical activity lowers the risk of prostate cancer1 and colon cancer.2 They hypothesized that physical activity might lower the risk of lung cancer. They analyzed the incidence of lung cancer among smokers as a function of their level of physical activity. More than 81,000 people were surveyed. Each person provided a self-reported level of physical activity both during work and at leisure.
Lung cancer was diagnosed in 413 men and 51 women during the course of the study. Among men, the risk of lung cancer decreased with increasing leisure-time physical activity. Men who exercised at least four hours a week had a 30% reduction in lung cancer risk (RR, 0.71; 95% CI, 0.54-0.98). For men active in their leisure time, the risk was particularly lowered for small cell lung cancer (RR, 0.59) and adenocarcinoma (RR, 0.65). There was no decreased risk of squamous cell lung cancer with exercise. Level of activity at work did not influence the risk, and women did not benefit from exercise at any level, though the number of cases of lung cancer in women may have been too small to detect a meaningful influence of exercise. The positive effect of exercise was greatest for men who smoked 15 or more cigarettes a day.
COMMENT BY DAN L. LONGO, MD
Squamous cell carcinoma has been the most common form of lung cancer in the United States for many years. However, recent epidemiological data suggest that adenocarcinoma has replaced squamous cell carcinoma as the most common histological subtype of lung cancer in the this country.3 It is not completely clear how physical activity modifies carcinogenesis. Nevertheless, the data seem quite convincing for a number of forms of cancer that regular exercise has cancer-preventive effects. Now, when a nicotine addicted person asks what he can do to prevent lung cancer besides quit smoking, we can say quit smoking and exercise at least four hours a week regularly. (Dr. Longo is Scientific Director, National Institute on Aging, Baltimore, MD.)
References
1. Thune I, Lund E. Cancer Causes Control 1994;5:549-556.
2. Thune I, Lund E. Br J Cancer 1996;73:1134-1140.
3. Travis WD, et al. Cancer 1995;75:191-202.
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