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

Fears using a phone at night may raise the risk of getting bowel cancer were raised today after a study found a link between the killer disease and blue light emitted by devices. 

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.

Results also showed exposure to outdoor blue light raised the odds of developing sleep disorders and becoming obese.

The study did not, however, focus on indoor artificial light or devices such as tablets and phones which emit blue light. 

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 tables and smartphones’.  

Using a mobile phone at night could increase the risk of bowel cancer by as much as 60 per cent, according to a new study

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

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

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.


Circadian rhythms are around 24-hours in length.

They vary from person to person – which is why some people are ‘morning people’ and others are ‘night owls’.

Natural factors within the body produce circadian rhythms as well as environmental signals such as daylight.

Irregular rhythms have been linked to various chronic health conditions, such as sleep disorders, obesity, diabetes and depression. 

Exposure to light suppresses the secretion of melatonin, a hormone that influences circadian rhythms and helps with sleep.

Melatonin levels rise in the evening and stay elevated throughout the night, promoting sleep. 

Artificial lighting and electronics with blue wavelengths trick the mind into thinking it’s daytime.  

How can you reduce your exposure?

  • Use dim red lights, which have the least effect on melatonin, for night lights. 
  • Avoid looking at bright screens beginning two to three hours before bed. 
  • If you work a night shift or use a lot of electronic devices at night, there are glasses and apps that can filter the blue light.  
  • Check if your phone settings have a night time setting which automatically shifts the display screen to warmer colours at sunset time.

‘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 World Health Organisation’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. 

And researchers didn’t take individual behaviour into account such as using rolling shutters, which is common in Spain.  

The estimate of exposure can therefore be interpreted as the amount of light people are exposed to when they are outside their homes and before shutting the blinds.

But 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. 

Bowel Cancer UK’s chief executive, Genevieve Edwards, told The Irish News: ‘While these new findings are interesting, the research isn’t able to take into consideration all of the other behavioural and lifestyle factors that might increase a person’s risk of developing bowel cancer. 

‘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.’  

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