Asbestos has also been linked to asbestosis, which is characterized by fibrosis of the lung and reduced lung function. In the 1950s, epidemiologists documented the link between lung cancer and asbestos exposure, especially in exposed workers who smoked.
Explore This IssueOctober 2006
U.S. asbestos-using industries have included insulation plants; textile plants; friction products plants; paper, packing, and asphalt products plants; cement pipe plants; and cement shingle, millboard, and gasket plants.
Although exposures in occupational settings have been much higher than those in residential settings, the committee pointed out that some activities in the home-such as shaking out work clothes of an asbestos worker-can approach the exposure levels found in the workplace.
The highest exposures have been among workers employed in plants that manufacture asbestos products, or those employed by mining and milling companies. Population exposure can occur not only through inhalation, but also through the consumption of asbestos in drinking water, the IOM committee found.
Asbestos can enter the drinking water supply from erosion of natural deposits, mining operations, or asbestos-containing cement pipes. As the science base has increased, exposure limits considered acceptable for occupational exposure to asbestos have dropped over time, the report found.
In exploring the link between asbestos and other cancers, if any, the committee reviewed 120 epidemiological studies of asbestos exposure and cancers of the throat and digestive tract. It also examined the evidence from about 200 experimental studies.
The base of evidence linking asbestos exposure causally to laryngeal cancer included more case-control studies-18-than were available for other cancer sites reviewed by the committee. The number of cohort populations, 35, was similar to those for stomach or colorectal cancer.
Exposed individuals in the studies reviewed by the committee had come in contact with asbestos in many industries and in many geographical areas, including North America, South America, Europe, and Japan.
For laryngeal cancer, the IOM committee identified consistency of findings among the epidemiologic studies. Further, it found that asbestos exposure was associated with increased risk of laryngeal cancer in all the nine larger cohort studies and in meta-analyses of the cohort and case-control data.
Evidence of Dose-Response Relationship
There was also some evidence of a dose-response relationship in both the cohort and case-control studies of asbestos exposure and cancer of the larynx. It was the consistency of study findings that led the committee to conclude that the evidence is sufficient to infer a causal relationship between asbestos exposure and laryngeal cancer.