Moderate to high levels of regular physical activity are associated with lower lung function decline among smokers and help to moderate their risk of developing chronic obstructive pulmonary disease (COPD), according to a large retrospective cohort study.
The research appears in the first issue for March 2007 of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
A cohort study is one in which a group of subjects are followed over time and compared with another group who are not affected by the condition being investigated. They are generally preferred to case control studies, since they involve far fewer statistical problems and generally produce more reliable results.
Judith Garcia-Aymerich, M.D., Ph.D., of the Center for Research in Environmental Epidemiology at the Institut Municipal d'Investigació Mèdica in Barcelona, Spain, and four associates assessed the physical activity, smoking history and lung function of 6,790 persons over 11 years. The investigators excluded individuals with COPD at the study's start.
"Prior to our study, the extent to which regular physical activity could reduce the risk of developing COPD was not known, but both epidemiologic and experimental studies indirectly supported this hypothesis," said Dr. Garcia-Aymerich.
COPD is the fourth-leading cause of death in the United States, killing 122,283 Americans in 2003. It results from chronic bronchitis and emphysema, two lung diseases which frequently co-exist and cause obstruction to airflow that interferes with normal breathing. Smoking is the primary cause of COPD.
Over the course of the 11-year study, 928 patients developed COPD. According to the authors, the reduction in COPD among smokers due to moderate to high levels of physical activity was 21 percent of potential new cases.
The investigators attribute this decline in new cases to regular exercise, which suppresses the production of inflammatory markers in the lungs caused by smoking, and reduces the pathogenesis of COPD.
Until now, smokers' only options for slowing lung function decline included stopping smoking and reducing occupational exposure to smoke. Therefore, Dr. Garcia-Aymerich and colleagues believe that their findings could offer smokers an important alternative.
"The interaction between physical activity and smoking should be taken into account when projecting the future burden of this respiratory disease," said Dr. Garcia-Aymerich.