Yale study links childhood thyroid cancer risk to air and light pollution

A new study led by researchers at Yale University suggests that early-life exposure to two widespread environmental pollutants- small particle air pollution and outdoor artificial light at night-could increase the risk of pediatric thyroid cancer.

The study-a collaborative effort involving multiple Yale departments and institutions across the U.S.-found a “significant association” between exposure to ambient fine particulate matter air pollution (PM2.5) and outdoor artificial light at night (O-ALAN) and increased risk of papillary thyroid cancer in children and young adults up to 19 years old. The exposures occurred during the perinatal stage of life, typically defined as the time from when pregnancy occurs up to a year after birth.

These results are concerning, especially given how widespread both of these exposures are. Fine particulate matter is found in urban air pollution due to automobile traffic and industrial activity, and artificial light at night is common, particularly in densely populated urban areas.”

Dr. Nicole Deziel, PhD, MHS, environmental epidemiologist with the Yale School of Public Health (YSPH) and study’s lead author

The research team analyzed data from 736 individuals diagnosed with papillary thyroid cancer before age 20 and 36,800 matched control participants based on birth year. Using advanced geospatial and satellite modeling, the team assessed individual-level exposure to PM2.5 and O-ALAN based on residential location at birth. All of the study participants were from California.

The findings showed that for every 10 micrograms per cubic meter increase in PM2.5 exposure, the odds of developing thyroid cancer rose by 7% overall. The strongest association between exposure and thyroid cancer was found among teenagers (15–19 years of age) and Hispanic children. Similarly, children born in areas with high levels of exposure to outdoor light at night were 23–25% more likely to develop thyroid cancer, according to the study.

“Thyroid cancer is among the fastest growing cancers among children and adolescents, yet we know very little about what causes it in this population,” said Deziel, an associate professor of epidemiology (environmental health sciences) and co-director of the Yale Center for Perinatal, Pediatric, and Environmental Epidemiology. “Our study is the first large-scale investigation to suggest that these exposures early in life-specifically to PM2.5 and outdoor light at night-may play a role in this concerning trend.”

In addition to Deziel, the research team included experts from Yale’s Departments of Biostatistics, Chronic Disease Epidemiology, and Pediatrics, as well as researchers from the University of Southern California, UC Berkeley, and the American Cancer Society. Deziel and several of the study’s authors are affiliated with the Yale Cancer Center. The team’s collective expertise ranged from environmental exposure modeling and biostatistics to pediatric endocrinology and cancer epidemiology.

The impact of papillary thyroid cancer on children can be extensive.

Compared to adults, children are often diagnosed with thyroid cancer at more advanced stages with larger tumor sizes. Pediatric survivors of thyroid cancer can suffer aftereffects ranging from temperature dysregulation and headaches to physical disabilities and mental fatigue. The disease can interfere with important life milestones such as education, employment, and raising a family and it can contribute to feelings of anxiety and depression.

Both PM2.5 and O-ALAN are considered environmental carcinogens that have been shown to disrupt the body’s endocrine system, including thyroid function, in animals and adults. The particles associated with PM2.5 pose a threat because they are small enough to enter the bloodstream and can interfere with hormone signaling, including those involved in regulating cancer pathways. Outdoor artificial light at night has been shown to suppress melatonin and alter circadian rhythms, which can also influence hormone-regulated cancer pathways.

The current research raises important environmental justice concerns. Communities of color and lower-income populations are often disproportionately exposed to both air pollution and light pollution-inequities that may contribute to the higher thyroid cancer burden observed in Hispanic children.

The researchers emphasized that more work is needed to replicate and expand on their findings, ideally using improved exposure metrics and longitudinal designs.

“In the meantime,” Deziel noted, “our results point to the critical importance of addressing environmental factors in childhood cancer research. Reducing exposures to air pollution and managing light pollution could be important steps in protecting children’s health.”

The study appears online in Environmental Health Perspectives.