A study from the Harvard T.H. Chan School of Public Health found that older adults exposed to PM2.5 and nitrogen dioxide air pollutants for more than a decade had an increased risk of colorectal and prostate cancer. Not only that, but even at low pollution levels, women are at increased risk of breast cancer, endometrial cancer, and the cancers listed above. By analyzing data on Medicare beneficiaries, the researchers also found that cancer risks varied across communities and demographics. This study highlights the urgency to revisit and strengthen U.S. air pollution standards.
New research led by Harvard T.H. Chan School of Public Health shows that long-term exposure to fine particulate matter (PM2.5) and nitrogen dioxide (NO2) in the air may increase the risk of non-lung cancer in older adults. In a study covering millions of Medicare beneficiaries, researchers found that exposure to PM2.5 and nitrogen dioxide increased the risk of colorectal and prostate cancer over a 10-year period. The findings also suggest that exposure to even minimal amounts of air pollution can predispose people to breast and endometrial cancer.
Wei Yaguang, a researcher in the Department of Environmental Health, said: "Our findings reveal the biological plausibility of air pollution as a key risk factor for the development of specific cancers and bring us one step closer to understanding the impact of air pollution on human health. To ensure that all populations have equitable access to clean air, we must fully understand the impact of air pollution and then work to reduce it."
The study was recently published in the journal Environmental Epidemiology.
Expanding the scope of air pollution research
Although air pollution has been identified as a risk factor for lung cancer and a link to breast cancer risk is emerging, few studies have focused on the impact of air pollution on the risk of prostate, colorectal, and endometrial cancer.
The researchers analyzed data collected from 2000 to 2016 on Medicare beneficiaries across the country who were 65 or older. All study subjects had been cancer-free for at least the first 10 years of the study period. The researchers created separate cohorts for each cancer—breast, colorectal, endometrial, and prostate—with 2.2 million to 6.5 million subjects in each cohort. The researchers analyzed the cancer risk of air pollutants in different subgroups based on factors such as age, gender (for colorectal cancer only), race/ethnicity, average body mass index and socioeconomic status.
Analyzing Data: Research Results and Implications
Using various sources of air pollution data, the researchers mapped projected PM2.5 and nitrogen dioxide concentrations in contiguous areas of the United States and then linked this to the zip code of a beneficiary's residence to estimate an individual's exposure over a 10-year period.
Long-term exposure to PM2.5 and nitrogen dioxide increases the risk of colorectal and prostate cancer, but is not associated with the risk of endometrial cancer, a nationwide analysis showed. In the case of breast cancer, exposure to nitrogen dioxide reduces cancer risk, while the relationship with PM2.5 is inconclusive. The researchers believe this mixed correlation may be due to differences in the chemical composition of PM2.5, a complex mixture of solid and liquid particles.
Their impact on breast cancer risk was even more pronounced when the analysis was restricted to areas where air pollution levels were significantly lower than national standards and where the composition of PM2.5 remained fairly stable. There was also a stronger association between exposure to both pollutants and endometrial cancer risk in areas with lower pollution levels.
In an analysis of risk by subgroup, the researchers found evidence that communities with higher average body mass index may face disproportionate risks of four cancers from exposure to nitrogen dioxide, and that Black Americans and those on Medicaid may be more likely to face cancer risks from exposure to PM2.5 (prostate and breast cancer, respectively).
Researchers note that even communities with seemingly clean air are not immune to cancer risks. They found that there was a substantial association between exposure to both pollutants and the risk of all four cancers, even at pollution levels below the World Health Organization's most recently updated standards, which are lower than current U.S. standards.
"The key message here is that U.S. air pollution standards are insufficient to protect public health," said senior author Joel Schwartz, professor of environmental epidemiology. "The Environmental Protection Agency recently proposed stricter PM2.5 standards, but their recommendations do not go far enough to regulate this pollutant. Current nitrogen dioxide standards are also woefully inadequate. Unless all of these standards become more stringent, air pollution will continue to cause thousands of unnecessary cases of multiple cancers each year."