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1 School of and Environmental Health and 2 Respiratory Division, Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
Correspondence and requests for reprints should be addressed to Susan M. Kennedy, Ph.D., School of Occupational and Environmental Hygiene, University of British Columbia, 2206 East Mall, Vancouver, BC, V6T1Z3, Canada. E-mail: susan.kennedy{at}ubc.ca
ABSTRACT
This workshop summary examines current research that addresses the question: Are women more susceptible than men to the effects of inhaled pollutants, namely those found in work or residential environments? A systematic literature review was performed in preparation for the workshop. A total of 73 recent (since 2000) articles were retrieved reporting on occupational and environmental exposures and their impact on chronic obstructive pulmonary disease, of which only nine provided gender-stratified results. In two mortality studies, results were contrary (one finding increased chronic obstructive pulmonary disease mortality in relation to traffic among elderly women compared with men, the other finding no gender difference). Two other environmental studies suggested small gender differences with slightly greater effect of biomass or traffic-related pollution among women. Four of five occupational studies also found increased effects of workplace pollutant exposure on measures of chronic airflow obstruction or bronchitis symptoms in women; again the differences were small. Preliminary findings from analysis of pooled data from six cross-sectional occupational surveys by our team also indicated increased relative risk for airflow obstruction in relation to work in industrial or service jobs among women compared with men, but only when airflow obstruction was measured using a gender-specific approach to determining the lower limit of normal. Workshop participants identified five key gaps and research needs, including the development of gender-sensitive tools for conducting future research in this area.
Key Words: occupational exposure • environmental exposure • chronic obstructive pulmonary disease • gender
There is growing evidence that chronic obstructive pulmonary disease (COPD) mortality and morbidity is rising among women relative to men, and it has been hypothesized that this may be linked to an increase in tobacco exposure or susceptibility among women (1, 2). Other evidence indicates that smoking rates among adult women have declined in parallel with men since the 1980s, at least in Western countries (3), suggesting that other factors must also be contributing to the apparent rise in COPD among women.
There is also considerable, strong evidence that the development of COPD is linked to occupational exposure to air pollutants, including inorganic and organic particulate matter as well as vapors/gases/fumes. Most such occupational studies have tended to focus on jobs held predominantly by men. As well, environmental exposure to biomass particulate matter has been strongly linked to COPD in developing countries. With a few exceptions, studies of biomass exposure have focused almost exclusively on women. Temporal spikes in ambient air pollution have been also linked to COPD exacerbations, although a causal link between ambient air pollutants and the new development of COPD is less evident.
If it is true that women are more susceptible than men to the effects of one inhaled pollutant (i.e., tobacco smoke), it raises the question: Are women more susceptible than men to the effects of other inhaled pollutants, namely those found in work, residential, or community environments? Very few studies of the health impact of occupational or environmental exposures have investigated gender differences in the outcomes or in exposure.
As part of the national workshop that is the focus of this issue of Proceedings, we performed a comprehensive review of epidemiologic studies that have investigated the specific association between COPD and environmental or occupational exposures and that presented at least some results from which gender-stratified findings could be extracted. The article focuses on recent studies (since 2000) to complement previous, more general reviews of occupational exposures and COPD conducted by one of the authors (4, 5). The previous reviews found no studies before 2000 reporting gender-stratified findings relating to COPD and occupational exposures.
Although in many recent studies occupational, residential, or ambient environmental exposures and gender have been examined for their potential impact on COPD, the overwhelming majority analyze sex or gender as one of many risk factors, hence controlling for gender or sex differences. Few studies have reported stratified analyses or considered sex or gender as an effect modifier. Of 73 articles retrieved that focused on occupational or environmental exposures and COPD, only nine were found in which gender-stratified results were presented: two that examined traffic related air pollution (6, 7), two evaluating biomass smoke exposure (8, 9), and five occupational studies (10–14).
AMBIENT AND RESIDENTIAL ENVIRONMENT EXPOSURES
Among Barcelona residents admitted to emergency rooms for COPD exacerbations, all-cause mortality and mortality from nonmalignant respiratory disease (mainly COPD) were associated with ambient black smoke levels in the week before death (6). This association was seen most strongly among women over the age of 80. In contrast, among patients with COPD in Mexico City followed for 7 years (8), crude survival rates were better for women than men, and crude survival was similar for women smokers and women nonsmokers with exposure to biomass smoke. However, when survival was adjusted for level of FEV1, oxygen saturation, body mass index, and age, there were no differences in survival between male smokers, female smokers, and female nonsmokers exposed to biomass smoke. Among Chinese farm residents born into homes with unvented coal stoves, COPD incidence was significantly reduced in association with the installation of a chimney among men and women; however, the reduction in incidence was less marked in women than in men (9). In younger adults (aged 25–40), Sunyer and colleagues found increased chronic phlegm and chronic cough associated with reported traffic levels among women but not among men (7).
OCCUPATIONAL EXPOSURES
Among young adults studied as part of the European Respiratory Health Survey (10), Sunyer and colleagues found no association between occupational exposures and airflow obstruction (prevalent or incident) in men or women but did find a significant association between occupational exposure to mineral dust, gases, and vapors and chronic phlegm in men but not in women. This is in contrast to the association seen in the same study (noted in the previous paragraph) between increased "exposure" to traffic and chronic bronchitis symptoms among women. In a similarly designed study, among a random sample of Australians, Matheson and colleagues (11) found that employment in a job with exposure to biological dust was a strong and significant risk factor for COPD in women (sevenfold increase in risk) but not in men (no increase in risk). The jobs with biological dust exposure held by women in this population included health care professions, food and textile workers, artists, and cleaners. Among participants in the Third National Health and Nutrition Examination Survey (NHANES III) study (12), COPD (using GOLD [Global Initiative for Chronic Obstructive Lung Disease] criteria) was significantly associated with employment in several job categories in the population as a whole, with reportedly higher associations seen in women than men among jobs in personal services, agriculture, textiles, rubber and plastics industries, and sales-related jobs. In a French study of nonmanual workers (13), the association between FEV1 and self-reported exposure to dust, gases, and fumes was slightly stronger in women than in men (a difference between "exposed" and "nonexposed" of 0.06 L [P = 0.06] in women vs. 0.04 L [P = 0.13] in men). However, in the same population, when exposure was classified using a population-specific job-exposure matrix, the effect of exposure on FEV1 was similar in women and men. Finally, in a 20-year follow-up study of Chinese cotton textile workers (14), a small improvement in airflow rates (reduced FEV1 decline) was seen among nonsmoking men after cessation of occupational exposure, whereas no such improvement was seen in women, despite higher dust and endotoxin exposures among the men in the study.
Taken together, these results provide only preliminary evidence that environmental or occupational exposure may contribute to chronic airflow obstruction differently in women and men. Although there were contrary findings, the majority of these few studies did find a slightly stronger impact of toxic air pollutants on COPD among women or no difference between the effect on men and women. There is suggestive evidence that women may have differential susceptibility to the effects of biological dusts or smoke from biological sources. These preliminary findings require further investigation to better understand and quantify the potential role of occupational and environmental exposures in contributing to the apparently growing prevalence of COPD among women.
KEY KNOWLEDGE GAPS AND FUTURE RESEARCH
Participants in this workshop identified the following key gaps and research needs to ensure that future studies would be better positioned to provide evidence about the possible differential effects of home and work environments on COPD among women and men.
As preliminary evidence of the importance of points 4 and 5 above, after the workshop we reported results from an analysis of pooled data from six cross-sectional surveys of working populations in British Columbia, Canada (n = 981 women, 4,863 men) in which the risk of airflow obstruction, defined as FEV1/FVC ratio below the lower limit of normal using NHANES prediction equations (15), was significantly elevated compared with men among female industrial workers and service workers but not among female office workers (Figure 1), taking into account differences in smoking, atopy, and history of asthma (16). As important as the fact of finding an elevated risk for airflow obstruction among women, we also found that risk comparisons between men and women differed depending on the definition of obstruction used. As pointed out by Roberts and colleagues with respect to age (17), we found that using the GOLD criterion for obstruction (FEV1/FVC ratio < 70%) differentially underestimated the prevalence of obstruction among women, presumably because a fixed ratio does not take into account absolute differences in lung or airway size. This emphasizes the need for use of gender-sensitive tools and analytic approaches in investigating potential sex and gender differences in COPD.
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FOOTNOTES
Supported by the Canadian Institutes of Health Research (Institute of Gender and Health), Canadian Tobacco Control Research Initiative, Interdisciplinary Capacity Enhancement: Bridging Excellence in Respiratory Disease and Gender Studies (ICEBERGS) (http://www.icebergs.ubc.ca).
This article was based on a national workshop discussion at the "Toward a Research Agenda on Gender and Chronic Obstructive Pulmonary Disease" conference in Vancouver, Canada.
Conflict of Interest Statement: None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript.
(Received in original form July 9, 2007; accepted in final form July 22, 2007)
REFERENCES
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