Do you have a street light outside your house? It could increase your cancer risk, scientists say
LIVING close to street lights could increase a woman’s risk of breast cancer, according to new research.
And women who frequently work under artificial lights, like night shift workers, are even more at risk of developing the disease, scientists say.
Researchers believe artificial light upsets a woman’s normal circadian rhythm – the body’s internal clock – which can disrupt natural biological processes.
It was also found to block a protective hormone that helps stave off the disease.
In the largest ever study of its kind, experts from Harvard Medical School found that as exposure to artificial light increased so did breast cancer rates.
But the link was found only among premenopausal women who were current or past smokers.
Professor Peter James, of Harvard Medical School, Boston, said: “In our modern industrialised society, artificial lighting is nearly ubiquitous.
“Our results suggest this widespread exposure to outdoor lights during night time hours could represent a novel risk factor for breast cancer.”
His team followed almost 110,000 participants across the US for 15 years.
Those in the top fifth for outdoor light exposure were 14 percent more likely to get breast cancer than those in the bottom fifth.
Prof James said previous studies have suggested it decreases the body's production of melatonin a hormone that anticipates the onset of darkness.
Typically, levels change throughout the day, reaching a peak in the evening while falling off during daytime hours.
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Women with less melatonin, such as those who work the night shift or sleep fewer hours, have been found to have a higher risk of breast cancer.
In the lab, melatonin has been shown to slow the growth of tumours.
Prof James added: “The association between outdoor light at night and breast cancer was found only among women who were premenopausal and those who were current or past smokers.
“In addition, the link was stronger among women who worked night shifts, suggesting exposure to light at night and night shift work contribute jointly to breast cancer risk, possibly through mechanisms involving circadian disruption.”
The study was published in the journal Environmental Health Perspectives.
An earlier study by Israeli scientists also found links between artificial light-at-night and breast cancer rates in a satellite analysis of 180 countries.
Countries in Western Europe showed the highest levels of association.
The same team also found men and women living in the most illuminated towns and cities were also more likely to be obese.
Experiments on mice by Belgian researchers also showed exposed to light 24 hours a day for five weeks put on 50 per cent more fat.
The results of several studies suggest women who work at night - factory workers, doctors, nurses, and police officers, for example - have a higher risk of breast cancer compared to women who work during the day.
Dr Richard Berks, of Breast Cancer Now, said the study required further investigation.
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He said: "In particular, we hope further studies will investigate how the exposure to light at night and breast cancer risk is further impacted by smoking or menopausal status, to understand the possible biological mechanisms behind these risk factors.
"In the meantime, we’d encourage any women concerned about their breast cancer risk to consider known risk-reducing options, such as regular physical activity, maintaining a healthy weight, and cutting down on alcohol, before moving to the country or sleeping at the back of the house."
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