Exposure to outdoor blue light may increase the risk of developing bowel cancer, scientists say

Outdoor blue light from billboards, as pictured in Piccadilly Circus, have been linked to bowel cancer risk

Blue light exposure at night has previously been linked to higher risk of prostate cancer and breast cancer.The latest study found that high levels of blue light exposure – from the likes of LED street lights and advertisement billboards – is associated with “a 60% increased risk” of bowel cancer.

Researchers led by the Barcelona Institute for Global Health (ISGlobal) looked at medical and epidemiological data of nearly 2,000 adults in Barcelona and Madrid, 660 of whom had bowel cancer.

Individuals with a history of working night shifts were excluded from the study due to its association with causing disruption the body’s 24-hour cycle, known as the circadian rhythm, and its links with bowel cancer risk.

Researchers used images taken by astronauts on the International Space Station to calculate the intensity of artificial light at night in the two Spanish cities.

The results found that participants with the highest exposure to blue light had a 60% higher risk of developing bowel cancer than the less-exposed population.

While its role in bowel cancer is unclear, scientists say studies have shown that disruption of circadian genes may contribute to the initiation and progression of bowel cancer.

It is believed that blue light can decrease the body’s production and secretion of the hormone melatonin, which plays a key role in regulating the circadian rhythm.

Dr Manolis Kogevinas, ISGlobal researcher and coordinator of the study, which was published in Epidemiology, said that research on the potential effects of light exposure on cancer “is still in its infancy” and needs more work.

He added: “We found an association only with blue light spectrum – this corresponds to the strong white light from hard LEDs and not with visual light.”

Researchers said no association has yet been found with other types of artificial light.

They added that the most recent study did not focus on indoor artificial light or devices such as tablets and phones which emit blue light.

However, Dr Kogevinas suggested that technology devices should be assessed because the public has “extensive exposure” to blue light through tablets and smartphones.

Commenting on the research, Genevieve Edwards, chief executive of Bowel Cancer UK, highlighted that the study did not consider “behavioural and lifestyle factors” that might increase bowel cancer risk.

She added: “We cannot tell from this study if artificial light directly led to people developing the disease.

“As the researchers acknowledge themselves, this area of work is in its infancy and we’d welcome further studies.”

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