Carried out by an international team led by the Barcelona Institute for Global Health (ISGlobal), the researchers looked at data from more than 4,000 people between 20 and 85 years of age in 11 Spanish regions, both with and without breast and prostate cancer.
The team assessed the participants' indoor exposure to artificial light using questionnaires, and evaluated outdoor levels of artificial light for Madrid and Barcelona, based on nocturnal images taken by astronauts aboard the International Space Station.
The results for the two cities showed that those who were exposed to higher levels of blue light had a 1.5-fold and two-fold higher risk of developing breast and prostate cancer, respectively, when compared to those who were less exposed.
Manolis Kogevinas, coordinator of the study, commented, "WHO's International Agency for Research on Cancer (IARC) has classified night shift work as probably carcinogenic to humans. 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."
"Given the ubiquity of artificial light at night, determining whether it increases or not the risk of cancer is a public health issue," added Ariadna García-Saenz, first author of the study. "At this point, further studies should include more individual data using for instance light sensors that allow measuring indoor light levels. It would also be important to do this kind of research in young people that extensively use blue light emitting screens."
Recent research has mainly focused on looking at the effect of blue light on sleep. Many studies have found that our increased use of devices such as smartphones and tablets could be to blame for the current global sleep epidemic, as the blue light emitted from screens suppresses production of the hormone melatonin, which we need to fall asleep.
Many experts now advise avoiding bright light and blue light from computer and phone screens for at least two hours before heading to bed.
The results were published online in Environmental Health Perspectives.