Nighttime exposure to blue light is associated with increased risk of colorectal cancer

July 31, 2020
An analysis in which rates of colon cancer were examined with respect to nighttime outdoor lighting showed a 60% higher risk for blue-rich lighting areas.

At one time, the most efficient and widely used outdoor street and urban lighting was high-pressure sodium lamps, which give off a pink-orange glow and have very little blue light in their spectrum. With the rise of gallium nitride (GaN)-based white-light LEDs, however, most sodium outdoor lighting has been replaced by blue-rich cool-white LED lighting.

Now, a team led by the Barcelona Institute for Global Health (ISGlobal; Barcelona, Spain), has conducted a study of the association between night-time exposure to outdoor artificial light and colorectal cancer; the findings show that nighttime exposure to the blue light in outdoor lighting may increase the risk of this type of cancer.1

Previous studies have found associations between nighttime exposure to artificial light -- especially blue light -- and various adverse health effects, including sleep disorders, obesity, and increased risk of various types of cancer, especially in night-shift workers. In fact, an earlier study by ISGlobal found a link between exposure to blue light at night and increased risk of breast and prostate cancer.2

“Using the same methodology as the previous study, we decided to analyze the relationship between exposure to artificial light and colorectal cancer, the third most common type of cancer worldwide after lung and breast cancer,” says Manolis Kogevinas, coordinator of the new study. The World Health Organization’s International Agency for Research on Cancer (IARC) classifies nightshift work as probably carcinogenic to humans; breast, prostate, and colorectal cancer are associated with the highest risk.

Analysis from ISS images

The authors analyzed data obtained through the MCC-Spain project on approximately 2000 adults in Barcelona and Madrid, of whom 660 had colorectal cancer and the rest randomly selected from the local population. Individuals with a history of working night shifts were excluded. Night-time levels of outdoor artificial light were determined using images from the International Space Station (ISS).

Results from both cities showed that participants with the highest exposures to blue light had a 60% higher risk of developing colorectal cancer than the less exposed population. No association was found with full-spectrum light.

“Night-time exposure to light, especially blue-spectrum light, can decrease the production and secretion of melatonin, depending on the intensity and wavelength of the light,” says Kogevinas.

Because exposure to light was estimated using satellite images, this calculation did not take into account individual behaviors such as the use of rolling shutters, which is common in Spain and other Mediterranean countries. The estimate of exposure can therefore be interpreted as the amount of light people are exposed to when they are outside their homes—a common pattern in Spain—and inside their homes before closing the shutters and going to bed.

“Research on the potential effects of light exposure is still in its infancy, so more work is needed to provide sound, evidence-based recommendations to prevent adverse outcomes,” adds Kogevinas.



1. Garcia-Saenz, A. et al., Epidemiology (July, 2020); doi: 10.1097/EDE.0000000000001226.

2. Garcia-Saenz, A. et al., Environmental Health Perspectives (2018);

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.

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