Modern street lamps and mobile phones are triggering thousands of cancer cases, according to new research.
A University of Exeter study found men living in large cities are twice as likely to develop prostate cancer while women are one and a half times more prone to breast cancer.
Scientists blame the worrying trend on the ‘blue light’ emitted by LEDs. This reduces levels of melatonin which controls the body clock.
Both forms of the disease have been linked to a lack of the hormone which is produced during sleep.
The alarming findings also add to concerns about blue light emitted by smartphones and tablets, Devon Live reports .
In the UK, hundreds of thousands of street lights have been replaced by LEDs which are cheaper to run and have lower emissions.
Dr Alejandro Sanchez de Miguel, of the University of Exeter, said: "Humans have evolved to need light during the day and darkness at night.
"As towns and cities replace older lighting, we are all exposed to higher levels of ‘blue’ lights, which can disrupt our biological clocks."
He said the same applies to outdoor commercial lighting, such as advertising.
"It is imperative that we know for sure whether this increases our risk of cancer.
"Scientists have long suspected this may be the case – now our innovative findings indicate a strong link.
"We must also investigate whether night-time exposure to the blue light emitted by smartphones and tablets increases our risk of cancer."
His team compared medical and epidemiological data of more than 4,000 men and women aged between 20 and 85 in 11 areas of Spain, mainly around Madrid and Barcelona.
The analysis led by the Barcelona Institute for Global Health (ISGlobal) found the bluer the light emission urban dwellers were exposed to, the higher the risk of cancer compared to those in suburban or rural regions.
It also showed those who lived in homes with darker rooms, by using window shutters for example, had lower risk.
Older lighting schemes let off a glow within the ‘orange’ spectrum, but new modern lighting creates a bright ‘blue’ emission.
Indoor exposure to artificial light was determined through personal questionnaires, with outdoor levels evaluated based on night-time images taken by astronauts aboard the International Space Station.
It was the first time this has been done.
Dr de Miguel, who has investigated light pollution for more than 20 years, said: "We must now improve our research methods to ensure this is robust so we can advise on how best to protect human health.
"Currently, the images taken by astronauts on the International Space Station are our only way of determining the spread of blue light-emitting white LEDs in our cities."
Melatonin is produced by a gland in the brain, principally between the hours of 9pm and 8am.
Lower levels can lead to increased levels of oestrogen, a suspected breast cancer trigger.
It can also lead to an increase in genetic mutations, reduced DNA repair and a weakened immune system, which may all raise the risk of prostate cancer.
The study published in Environmental Health Perspectives said little is known about how environmental factors affect breast and prostate cancer.
It is believed LED lights disrupt the body’s 24-hour cycle known as the circadian rhythm, in turn affecting hormones.
Both breast and prostate cancer are hormone-related.
Previous research has shown an increased risk between prostate cancer and night shift work.
It is also known that artificial light, particularly in the blue spectrum, can decrease the body’s production and secretion of the hormone melatonin.
Melatonin plays a key role in regulating the day-night cycles and has several other key functions.
It is a powerful antioxidant and an anti-inflammatory function. But its role in breast and prostate cancer is not yet understood.
Dr Manolis Kogevinas, head of the Cancer Research programme at ISGlobal, The Barcelona Institute for Global Health, who coordinated of the study, said: "The World Health Organisation’s International Agency for Research on Cancer (IARC) has classified night shift work as probably carcinogenic to humans.
"There is evidence pointing to an association between exposure to artificial light at night, disruption of the circadian rhythm, and breast and prostate cancers.
"With this study we sought to determine whether night exposure to light in cities can affect the development of these two types of cancer."
Co author Professor Martin Aube, a physicist at CEGEP (General and Vocational College), Quebec, said: "We know depending on its intensity and wave length, artificial light, particularly in the blue spectrum, can decrease melatonin production and secretion."
Added first author Dr Ariadna Garcia, of ISGlobal: "Given the ubiquity of artificial light at night, determining whether or not it increases the risk of cancer is a public health issue.
"At this point, further studies should include more individual data using for instance light sensors that allow measuring indoor light levels.
"It would also be important to do this kind of research in young people that extensively use blue light emitting screens."
In the UK, prostate cancer is now the third most deadly form of the disease, killing almost 12,000 men a year.
Breast cancer is next, claiming around 11,500 lives, annually.
Councils claim LED lights reduce energy use by up to 40 per cent.
Earlier this month it was revealed Kent County Council is installing 118,000 on its streets, Leicestershire plans to have 68,000, Manchester 56,000 and Gloucestershire 55,000.
There are five times fewer cases of breast cancer in developing countries, where electric light is less widespread, than in industrialised nations.
Claims that shift work – carried out by 2 million women in Britain – could lead to breast cancer first emerged in 1987, although subsequent studies have failed to establish a definitive link.
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