Abstract
BackgroundGrowing evidence suggests that air pollution may be a risk factor for breast cancer, but the biological mechanism remains unknown. High mammographic density (MD) is one of the strongest predictors and biomarkers of breast cancer risk, but it has yet to be linked to air pollution. We investigated the association between long-term exposure to traffic-related air pollution and MD in a prospective cohort of women 50 years and older.MethodsFor the 4,769 women (3,930 postmenopausal) participants in the Danish Diet, Cancer and Health cohort (1993–1997) who attended mammographic screening in Copenhagen (1993–2001), we used MD assessed at the first screening after cohort entry. MD was defined as mixed/dense or fatty. Traffic-related air pollution at residence was assessed by modeled levels of nitrogen oxides (NOx) and nitrogen dioxide (NO2). The association between mean NOx and NO2 levels since 1971 until cohort baseline (1993–97) and MD was analyzed using logistic regression, adjusting for confounders, and separately by menopause, smoking status, and obesity.ResultsWe found inverse, statistically borderline significant associations between long-term exposure to air pollution and having mixed/dense MD in our fully adjusted model (OR; 95% CI: 0.96; 0.93-1.01 per 20 μg/m3 of NOx and 0.89; 0.80- 0.98 per 10 μg/m3 of NO2). There was no interaction with menopause, smoking, or obesity.ConclusionTraffic-related air pollution exposure does not increase MD, indicating that if air pollution increases breast cancer risk, it is not via MD.Electronic supplementary materialThe online version of this article (doi:10.1186/s12940-015-0017-8) contains supplementary material, which is available to authorized users.
Highlights
Breast cancer is the most common type of cancer and one of the leading causes of death among women in the western world [1]
We excluded 1,158 who did not participate in mammographic screening after cohort recruitment, 646 women who were positive at the first screen after recruitment, and 934 who lacked air pollution data, leaving a total of 4,769 participants in the final analytic data set
We found no convincing association between exposure to traffic-related air pollution and mammographic density (MD)
Summary
Breast cancer is the most common type of cancer and one of the leading causes of death among women in the western world [1]. Breast cancer incidence is higher in more industrialized countries, as well in urban areas, suggesting, among other factors, a possible relevance of air pollution [3,4]. Epidemiological evidence is limited and mixed, but seems to increasingly suggest that air pollution, both from industrial sources [5,6] and traffic emissions [7,8,9,10,11] may increase breast cancer risk. The strongest evidence exist for the association of nitrogen dioxide (NO2), traffic related air pollutant, with breast cancer risk, provided by two Canadian case–control studies [8,11]. Growing evidence suggests that air pollution may be a risk factor for breast cancer, but the biological mechanism remains unknown. We investigated the association between long-term exposure to traffic-related air pollution and MD in a prospective cohort of women 50 years and older
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