Exposure of Artificial Nighttime Light Linked to Thyroid Cancer

A new study shows that people living in regions with high levels of artificial light at night face a higher risk of developing thyroid cancer. The study was published in the journal CANCER.

In this study, researchers tracked 464,371 participants over an average of 12.8 years. Over that span, 856 cases of thyroid cancer were diagnosed (384 in men and 472 in women). The results showed that compared with the lowest quintile of light at night, the highest quintile was associated with a 55% higher risk of developing thyroid cancer. The association was primarily driven by the most common form of thyroid cancer, and it was stronger in women than in men, the researchers noted. They observed that in women, the association was stronger for localized cancer with no sign of spread to other parts of the body, while in men the association was stronger for more advanced stages of cancer.


“As an observational study, our study is not designed to establish causality. Therefore, we don’t know if higher levels of outdoor light at night lead to an elevated risk for thyroid cancer; however, given the well-established evidence supporting a role of light exposure at night and circadian disruption, we hope our study will motivate researchers to further examine the relationship between light at night and cancer, and other diseases,” said Qian Xiao, PhD, of The University of Texas Health Science Center at Houston School of Public Health via a press release. “Recently, there have been efforts in some cities to reduce light pollution, and we believe future studies should evaluate if and to what degree such efforts impact human health.”