Artificial LAN May Increase Risk for Thyroid Cancer

A cohort study has shown that exposure to artificial light at night (LAN) was associated with increased thyroid cancer risk (Cancer. 2021 Feb 8. Epub ahead of print).

According to the researchers, LAN prevents melatonin production and can disrupt circadian rhythm, which may be associated with an increased risk of developing cancer. Because recent studies associated high LAN exposure with elevated breast cancer risk, lead investigator Dong Zhang, PhD, Department of Family and Preventive Medicine, University of Arkansas for Medical Sciences, Little Rock, and colleagues wanted to see if that risk was also present with thyroid cancer.

“Given that breast cancer may share a common hormone‐dependent etiology with thyroid cancer and that circadian rhythms play a role in regulating thyroid function, [we] hypothesized that exposure to LAN is positively associated with thyroid cancer incidence,” explained Dr Zhang et al.

The study took place in the National Institutes of Health-American Association of Retired Persons Diet and Health Study. To estimate LAN exposure, satellite data was linked to residential addresses at the baseline, while incident thyroid cancer cases were verified through state cancer registries.

The relationship between LAN and thyroid cancer risk was determined through COX regression, and adjustments were made for sociodemographic, lifestyle, and other environmental factors. 

A positive association between LAN and thyroid cancer risk was found amongst 464,371 participants. It was noted that, when compared to the lowest quintile of LAN, the highest quintile saw a 55% increase in risk (hazard ratio [HR], 1.55; 95% CI, 1.18-2.02).

Dr Zhang and co-investigators also discovered that the connection was primarily driven by papillary thyroid cancer and was stronger in women than men. However, women were more likely to be associated with localized cancer, while men were linked to a more advanced stage. Results stayed consistent across various tumor sizes. 

“LAN was positively associated with thyroid cancer risk. Future studies are needed to confirm this association and identify underlying biological mechanisms,” they concluded.—Alexandra Graziano