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Cities around the world are increasingly turning to streetlights emitting so-called "blue light," and it's also common in smartphones, laptops and tablets. Now, a study hints that excess exposure to blue-spectrum light might raise a person's odds for colon cancer.
As a team of Spanish researchers noted, prior studies have suggested that blue light emitted by most white LEDs (light-emitting diodes) and many tablets and phones was linked to ailments such as sleep disorders, obesity and an increased risk of various cancers, especially among night-shift workers.
One study also found a link between blue light and an increased risk of breast and prostate cancer, the researchers said.
"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," researcher Manolis Kogevinas, of the Barcelona Institute for Global Health, said in an institute news release.
For the study, Kogevinas and colleagues tracked data on about 2,000 adults living in Barcelona and Madrid. Of this group, 660 had colon cancer while the rest were randomly selected from the general population. People who worked night shifts were excluded from the research.
The study wasn't able to determine that blue light exposures caused colon cancer, it could only point at associations. However, people with the highest exposures to blue light had a 60% higher risk of developing colon cancer compared to those who were less exposed, the researchers reported.
There could be physiological reasons for the effect Kogevinas explained.
"Nighttime exposure to light, especially blue-spectrum light, can decrease the production and secretion of melatonin, depending on the intensity and wavelength of the light," he said.
"There is growing concern about the effects of light on ecosystems and human health. 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," Kogevinas added.
The research team stressed that it was tough to account for certain factors in their research. For example, the group relied on satellite imaging to gauge the amount of blue light emitted at night in various locales. But the study couldn't account for the nighttime use of light-barring rolling shutters on windows -- a common feature on Spanish housing. So the study is really trying to assess exposure to light when people are outside at night, the team said.
One U.S. expert in gastrointestinal disease called the study "interesting."
The research is "expanding the idea of light pollution to something that may have biological consequences," said Dr. Arun Swaminath, who directs the Inflammatory Bowel Disease Program at Lenox Hill Hospital in New York City.
Still, there are many unanswered questions, he said, especially the fact that participants' blue light exposure "was obtained by history taking, but it couldn't account for things like blinds/curtains that would affect how much exposure some had to light."
The report was published online July 29 in the journal Epidemiology.
-- E.J. Mundell
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