Could using your mobile phone at night raise your risk of bowel cancer?

Using a mobile phone at night is feared to increase the risk of bowel cancer after a study investigated blue light emitted by LED. Blue light is a range of the visible light spectrum emitted by most white LEDs, such as ones used in street lamps, and many tablet and phone screens.

Researchers at the Barcelona Institute for Global Health studied 1,983 adults who live in Barcelona and Madrid, 661 of whom had bowel cancer.

Satellite images from the International Space Station were used to study the levels of outdoor blue light exposure, coming from street lights and billboards. Those who lived in areas with the highest exposure to blue light had a 60 per cent higher risk of developing bowel cancer, according to the findings. Scientists also found that exposure to outdoor blue light increased the odds of developing sleep disorders and becoming obese.

The study did not focus on indoor artificial light or devices such as tablets and phones which emit blue light, the researchers said. But the lead researcher, Dr Manolis Kogevinas, suggests technology devices should be assessed because 'the general population and also young ages have extensive exposure to blue light through tablets and smartphones'.

The blue artificial light that phones emit at night has previously been linked to an increased chance of being diagnosed with breast and prostate cancer.

Bowel cancer is the second most deadly cancer and affects roughly 268,000 in the UK. Some 16,000 people die from it every year.

Dr Kogevinas, ISGlobal researcher and coordinator of the study published in Epidemiology, said that research on the potential effects of light exposure on cancer 'is still in its infancy.

'More work is needed to provide sound, evidence-based recommendations to prevent adverse outcomes,' he said.

The research excluded anyone who worked night shifts because the WHO's International Agency for Research on Cancer (IARC) classifies night- shift work as probably carcinogenic.

Blue light has long been suspected to be the reason that night shift workers, exposed to artificial light for longer, have a greater risk of cancer.

Dr Kogevinas said: 'We found an association only with blue light spectrum - this corresponds to the strong white light from hard LEDs and not with visual light.'

The risks were similar even when the researchers accounted for other risk factors for cancer, including socioeconomic status, diet, smoking, sleep and family history.

Blue light is emitted by most white LED lamps, mobile phones, tablets and devices like Kindles. The light which glows from electronic devices is already believed to disrupt our body clocks because close exposure to blue light has been found to drain people's melatonin levels. Melatonin not only helps to regulate sleep patterns, known as a circadian rhythm, but is also thought to regulate inflammation.

Although its role in bowel cancer is unclear, the researchers say studies have shown that disruption of circadian genes, which effects hormone levels, may contribute to developing bowel cancer.

Dr Kogevinas said: '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.'

Both breast and prostate cancer are hormone related.

The team previously found that people exposed to high levels of outdoor blue light at night had double the risk of developing prostate cancer and 1.5 times the risk of developing breast cancer.

The Barcelona Institute for Global Health's study was published in the journal, Epidemiology.