The Grapevine

Artificial Light At Night Linked To Breast, Prostate Cancer Risk: Study

Any chance you happen to be reading this article in the middle of the night on your phone or tablet? Researchers from the Barcelona Institute for Global Health (ISGlobal) hope not.

A new study led by an international team from the institute has reported a link between exposure to blue light at night and an increased risk of developing breast and prostate cancer. The paper titled "Evaluating the Association between Artificial Light-at-Night Exposure and Breast and Prostate Cancer Risk in Spain" was published in the journal Environmental Health Perspectives on April 23.

The research team examined data of more than 4,000 people in 11 different regions of Spain. It included 1,219 breast cancer cases, 623 prostate cancer cases, 1,385 female controls and 879 male controls. All the participants were enrolled in 2008–2013 and were between 20 and 85 years of age.

Both human and animal studies have suggested that the disruption of circadian rhythms of the body (caused by exposure to light at night) may contribute to the growth of tumors. Artificial light, typically sourced from smartphones and white LEDs, contain a larger blue light component.

"Night shift work, exposure to light at night and circadian disruption may increase the risk of hormone-dependent cancers," the authors wrote. According to the International Agency for Research on Cancer (IARC), jobs that involve night shifts are "probably carcinogenic" to workers.

"There is evidence pointing to an association between exposure to artificial light at night, disruption of the circadian rhythm, and breast and prostate cancers. With this study we sought to determine whether night exposure to light in cities can affect the development of these two types of cancer," explained Manolis Kogevinas, a researcher from ISGlobal, who coordinated the study.

The next step was to measure the levels of artificial lighting in both indoors and outdoors. While personal questionnaires were used for the former, outdoor levels of artificial light were determined using night-time images taken by astronauts on the International Space Station. Nocturnal images of both Madrid and Barcelona were obtained as they helped the researchers determine the color of outdoor lighting and the spread of blue light-emitting LEDs on a large scale.

According to results for both the cities, participants exposed to higher levels of blue light had a 1.5 higher risk of developing breast cancer and a two-fold increase in the risk of developing prostate cancer when compared to the less-exposed population. In 2017, a similar study from Harvard Medical School found a link between light exposure at night and breast cancer among nurses who worked night shifts.

The key factor appears to be melatonin, a hormone produced by the pineal gland which helps the body know when to sleep and wake up.

"We know that depending on its intensity and wavelength, artificial light, particularly in the blue spectrum, can decrease melatonin production and secretion," said co-author Dr. Martin Aubé, a professor of physics at Cégep de Sherbrooke in Canada.

However, the study was limited due to self-reported data while more research is required to compare artificial lights to other cancer risk factors. Ariadna García, ISGlobal researcher and first author, stated that future studies should consider "light sensors that allow measuring indoor light levels" to help solidify the findings.