While smoking still accounts for most of the 16 million cases of chronic obstructive pulmonary disease, or COPD, the finding that occupational exposure may contribute to the illness in three to five million people strongly suggests a need for better workplace prevention, the researchers say. Their study is based on interviews of more than 2,000 people.
COPD involves chronic lung inflammation, a narrowing of the airways and increasingly severe breathing difficulties. It is the fourth highest cause of death in the U.S., killing more than 100,000 people a year. Worldwide, COPD kills three million people every year and is expected to become the third most common cause of death within 15 years. Annual direct and indirect costs of the disease in the U.S. have been estimated at more than $30 billion, according to NIH statistics.
"Although smoking prevention remains paramount, controlling hazardous exposures can also have an important role in reducing COPD," said Paul Blanc, MD, senior author of the study and UCSF professor of occupational and environmental medicine, and of pulmonary and critical care.
The research team's findings are being published in the September issue of the European Respiratory Journal.
The study found that chronic bronchitis, emphysema and related diseases are twice as frequent in people who have been exposed to toxic airborne substances in the workplace, regardless of whether or not they smoke. Workplace exposure has long been suspected in the disease, but no definitive studies have been carried out to quantify the proportion of cases contributed by the workplace.
Researchers interviewed more than 2,000 people in the U.S., aged 55 to 75, by telephone, asking them about their respiratory health and their work histories. Subjects were randomly selected from all over the United States. The 55-75 age group represents the peak incidence of COPD. (More than 40,000 households were initially contacted, but those without members 55 to 75 were eliminated from the survey, as were those unwilling or unable to participate.)
More than half of the people with COPD reported that they had been exposed to airborne toxins in the workplace, while only one in three of those free of respiratory disease reported such exposure. Analysis of the results showed that exposure to various workplace toxins doubles the risk of COPD, and that workplace exposure is a contributing cause of 20 to 31 percent of the diagnosed COPD cases.
Less than 20 percent of those suffering from COPD were still working – half the percentage of those without COPD -- underscoring the physical and financial toll of the disease.
"Given the severe impact of COPD, it is critical to identify all possible avenues of exposure," said Laura Trupin, MPH, an epidemiologist in the UCSF Department of Medicine and lead author on the study. "These findings direct us to look beyond the cigarette when we consider prevention of chronic lung disease."
While smoking remains the predominant cause of COPD, the study's authors conclude that "the workplace environment plays an important role too...clinicians and public health policymakers must also take workplace conditions into account when establishing preventive strategies."
The team focused on each subject's longest period of workplace exposure to vapors, gases, dusts or fumes. In addition to the information provided by the respondents on what they may have inhaled, the scientists relied on data from the European Community Respiratory Health Survey, which identifies the degree of exposure to toxic substances for each type of job.
In the study, occupational risk factors were classified in three categories. Vapors, gases and smoke released by the combustion of various materials were associated mainly with blast-furnaces and foundries, work with diesel engines and firefighting. Miners and metalworkers were the group most exposed to non-organic dust and smoke, while farmers, bakers and textile workers were mainly exposed to organic dust.
Colleagues in the research and co-authors on the paper are: Gillian Earnest, MS, statistician in the division of occupational and environmental medicine; Melanie San Pedro, BS, project coordinator; John Balmes, MD, professor, and Mark Eisner, MD, assistant professor, both of occupational and environmental medicine; Edward Yelin, PhD, adjunct professor, and Patricia Katz, PhD, associate adjunct professor, both in medicine and rheumatology. All positions at UCSF; Balmes is at the UCSF-affiliated San Francisco General Hospital Medical Center.
The study was funded by the National Institutes of Health.
Journal
European Respiratory Journal