WORKING nights does not increase a woman’s risk of breast cancer, a major study reveals.
The World Health Organisation has previously warned that doing late shifts is a likely trigger for the disease.
But British researchers, who followed more than 100,000 women over a decade, found no evidence overnight work raises the chances of developing breast cancer.
Experts said the new findings will reassure women whose jobs involve night shifts or early mornings.
The link was first suggested in the 1970s, when scientists claimed exposure to electric light may increase the risk of developing the disease.
One theory was that it disrupted the body’s internal clock, suppressing levels of the sleep hormone melatonin and raising oestrogen levels.
But the new analysis in the British Journal of Cancer dismissed the fears as unfounded.
Lead researcher Dr Michael Jones, from the Institute of Cancer Research in London, said: “A possible link between exposure to electric light at night and an increased risk of breast cancer was first proposed more than 30 years ago, but research has so far been inconclusive.
It is reassuring to see more evidence suggesting that night shifts are not linked with a higher risk of breast cancer
Dr Michael Jones, from the Institute of Cancer Research in London
“In our new study, we found no overall link between women having done night shift work in the last ten years and their risk of breast cancer – regardless of the different types of work they did involving night shifts, and the age at which they started such work.
“Although night shifts may have other effects on people’s health, and we still don’t know the effect of a person’s body clock being disturbed for very long periods of time, it is reassuring to see more evidence suggesting that night shifts are not linked with a higher risk of breast cancer.”
The study, which included data from 102,869 UK women, was funded by charity Breast Cancer Now.
The average age of participants was 45, with more than one in six reporting they had worked night shifts in the past ten years.
More than 55,000 women are diagnosed with breast cancer in the UK each year, with 11,500 dying.
Baroness Delyth Morgan, chief executive at Breast Cancer Care and Breast Cancer Now, said: “We hope these findings will help reassure the hundreds of thousands of women working night shifts that it’s unlikely their job patterns are increasing their risk of breast cancer.
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“This question has been widely debated in recent decades and has understandably caused concern, and it’s encouraging that the evidence now suggests night shift work has no impact on breast cancer risk.
“Whilst there are some things we can’t change, there are steps all women can take to lower their breast cancer risk, such as maintaining a healthy weight, keeping physically active and drinking less alcohol.
“Even small changes are a great start.”
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