Black women exposed to ozone air pollution have an increased risk of developing fibroids, according to new research published in Human Production.
Uterine fibroids are a common type of pelvic growth, affecting up to 80% of women by the time they reach age 50, according to the U.S. Department of Health and Human Services. Black women are hit hardest by fibroids; they are diagnosed two to three times the rate of White women and tend to have more severe symptoms.
Researchers are unclear on why exposure to ozone air pollution increases the risk of developing fibroids. However, they believe that when it comes to identifying causes of fibroids and explanations for racial disparities in fibroids, more research that focuses on environmental and neighborhood-level risk factors could help inform policy and interventions to improve gynecologic health.
“A large body of literature from the environmental justice field has documented that people of color, and Black people specifically, are inequitably exposed to air pollution,” study author Amelia K. Wesselink, PhD, assistant professor at Boston University School of Public Health, said in an interview. “And there is growing evidence that air pollution can influence gynecologic health and therefore may contribute to racial disparities in gynecologic outcomes.”
Dr. Wesselink and colleagues wanted to know the extent to which three air pollutants – particulate matter (PM2.5), nitrogen dioxide (NO2) and ozone (03) – were linked to the development of fibroids. To figure this out, they analyzed data on nearly 22,000 premenopausal Black women who lived in 56 metropolitan areas in the United States between 2007 and 2011. They assigned air pollution exposures to participants’ residential addresses collected at baseline and over follow-up and tried to capture long-term exposure to air pollutants.
During the study, nearly 30% of participants reported that they were diagnosed with fibroids. Researchers observed that the exposure to PM2.5 and NO2 was not associated with an increased risk of developing these fibroids.
Dr. Wesselink said the findings may have underestimated fibroid incidence, so they “need to be replicated in a prospective, ultrasound-based study that can identify all fibroid cases.”
“There has not been a lot of research on how air pollution influences fibroid risk, but the two studies that are out there show some evidence of an association,” said Dr. Wesselink. “The fact that our results were consistent with this is interesting. The surprising part of our findings was that we observed an association for ozone, but not for PM2.5 or NO2.”
Nathaniel DeNicola, MD, MSHP, FACOG, a Washington-based obstetrics and gynecology physician affiliated with John Hopkins Health System, applauded the methodology of the study and said the findings prove that patients and doctors should be talking about the environment and exposures to air pollutants.
“[Air pollution] has numerous components to it. And we should try to figure out exactly what components are most dangerous to human health and what doses and what times of life,” said Dr. DeNicola, an environmental health expert.
The increased risk of developing fibroids is a “historical observation” and air pollution may be part of a multifactorial cause of that, Dr. DeNicola said. He said he wouldn’t be surprised if future studies show that “higher exposure [to air pollution] – due to how city planning works, often communities of color are in the areas with the most dense air pollution – exacerbates some other mechanism already in place.
Although it’s unclear how ozone exposure increases fibroid risk, Dr. Wesselink said it may be through a mechanism that is unique to ozone.
“In other words, it might be that there is a factor related to ozone that we did not account for that explains our findings. Vitamin D is a factor that we were not able to account for in this study,” Dr. Wesselink said. “Future work on this topic should consider the role of vitamin D [exposure or deficiency].”
Dr. DeNicola said ozone’s impact may also be tied to its “known association” with hypertension. A 2017 study by Drew B. Day, PhD, of Duke University, Durham, N.C., and colleagues, found that ozone exposure has been linked to hypertension. Meanwhile, a 2015 study has found an association between hypertension and fibroids.
“[This study] does raise an important message. It shines a light where more research needs to be done,” Dr. DeNicola said. “The ozone connection to hypertension was probably most compelling as a true risk factor for uterine fibroids.”
Dr. Wesselink said future work on fibroid etiology should focus on environmental and neighborhood-level exposures to pollutants.