More than 80% of people who die from COPD are current or former smokers. The longer a person smokes, the higher the risk for emphysema. Most patients have smoked the equivalent of one pack a year for 20 years, and many have smoked for up to the equivalent of 40 years. Once a smoker quits, the rate of lung function loss becomes the same as in a nonsmoker; however, much of the lung damage that occurred during smoking may not be reversible.
People who smoke both tobacco and marijuana face nearly three times the risk of developing COPD compared to nonsmokers, although smoking marijuana alone does not seem to increase the risk. Researchers say there may be a synergistic effect, in which marijuana increases the susceptibility of the airways to the detrimental effects of tobacco smoke.
Emphysema caused by smoking most often occurs in the upper lobes of the lungs.
In chronic bronchitis, smoking triggers inflammation that causes damage in the airways. The processes involved include:
- Damage to the cilia, the hair-like waving projections that move mucus, bacteria, and foreign particles out of the lungs. When cilia are injured, these substances become trapped in the lungs and can cause infections that lead to chronic bronchitis.
- Enlargement of the mucus glands in the large airways of the lungs.
- Excess growth of smooth muscle cells in the airway.
Other Exposures
Smoking tobacco is a major risk factor for COPD, yet an estimated 25% to 45% of COPD patients in the developing world have never smoked. In underdeveloped countries, exposure to industrial pollutants in poorly ventilated work areas, and cooking over wood and coal fires are also major contributors.
Researchers say exposure to smoke from biomass fires might actually pose the biggest risk for COPD around the world. Other exposures that might increase COPD risk include:
- Dust
- Gases
- Outdoor air pollution
Genetics
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Review Date: 04/10/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine,
Harvard Medical School; Physician, Massachusetts General Hospital.
Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M.,
Inc.
A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)
