Outdoor air pollution may raise the risk for non-lung cancer in older adults, with even low levels of air pollution exposure increasing the chances for prostate, colorectal, breast, and endometrial cancers.
That’s according to a new Harvard T.H. Chan School of Public Health study of millions of Medicare beneficiaries. The researchers found that chronic exposures to fine particulate air pollutants (PM2.5) and nitrogen dioxide (NO2) over a 10-year period increased the risk of developing cancer.
PM2.5 has been in the news during the last couple of months because that’s the concerning air pollutant from the Canadian wildfire smoke, which has wreaked havoc across the U.S.
While air pollution in the past has been established as a risk factor for lung cancer — and a link to breast cancer risk has been emerging — few studies have looked at its effects on prostate, colorectal, and endometrial cancer risk.
“Our findings uncover the biological plausibility of air pollution as a crucial risk factor in the development of specific cancers, bringing us one step closer to understanding the impact of air pollution on human health,” said Yaguang Wei, research fellow in Harvard T.H. Chan School of Public Health’s Department of Environmental Health.
“To ensure equitable access to clean air for all populations, we must fully define the effects of air pollution and then work towards reducing it,” Wei added.
Researchers in the study looked at data from Medicare beneficiaries aged 65 or older, collected from 2000 to 2016. All subjects were cancer-free for at least the initial 10 years of the study period.
The researchers created separate cohorts for each type of cancer — breast, colorectal, endometrial, and prostate — with between 2.2 million and 6.5 million subjects in each cohort.
The scientists were then able to create a predictive map of PM2.5 and NO2 concentrations across the country. This was then linked to beneficiaries’ ZIP codes, so the researchers could estimate individual exposures over a 10-year period.
The researchers found that chronic PM2.5 and NO2 exposures increased the risk of developing colorectal and prostate cancers.
For breast cancer, NO2 exposure was tied to a lower risk, while the association for PM2.5 was inconclusive. In regions where air pollution levels were significantly below national standards and the composition of PM2.5 remained stable, their effect on breast cancer risk was more pronounced.
Also, stronger links between pollutant exposures and endometrial cancer risk were found at lower pollution levels.
The researchers noted that even communities with seemingly clean air were not immune to cancer risk. They found substantial associations between exposure to the two pollutants and the risks of all four cancers even at pollution levels below newly updated World Health Organization guidelines.
“The key message here is that U.S. air pollution standards are inadequate in protecting public health,” said senior author Joel Schwartz, professor of environmental epidemiology. “The Environmental Protection Agency recently proposed stricter standards for PM2.5, but their proposal doesn’t go far enough in regulating this pollutant.
“Current NO2 standards are also woefully inadequate,” Schwartz added. “Unless all of these standards become much, much stricter, air pollution will continue to result in thousands of unnecessary cases of multiple cancers each year.”
