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UK review appears to debunk link between night shift work and breast cancer

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Night shift work has “little or no effect” on breast cancer incidence, according to a new scientific review by UK researchers, which is in contrast with findings from previous studies.

As reported by Nursing Times, a number of observational studies have drawn a link between working at night and increased cancer risk, because such shifts disrupted the circadian rhythm.

The authors of the new review highlighted in particular an assessment by the World Health Organization in 2007, which indicated that night shifts were probably carcinogenic.

The conclusion, by the WHO’s International Agency for Research on Cancer, was based on evidence about breast cancer in animal studies due to limited evidence about such risk in humans.

But the authors of the new paper, published in the Journal of the National Cancer Institute, said data from three major UK studies and a review of available evidence indicated no such link.

“Night shift work, including long-term shift work, has little or no effect on breast cancer incidence”

Study authors

The researchers, from Oxford University, looked at data on a total of 800,000 women and estimated the relative risks of breast cancer among those who reported night shift work versus none.

They said no increase in breast cancer risk associated with night shifts, including working them long-term, was found in any of the studies involved – Million Women Study, EPIC-Oxford and UK Biobank.

No link was found either in a meta-analysis of worldwide evidence, which combined results from the three UK studies with two from the US, two in China, two in Sweden, and one in the Netherlands.

The 10 studies included a total of 1.4 million women among whom 4,660 breast cancers occurred in women who reported ever having done night shift work.

Compared with women who did not work nights, the combined relative risk from all 10 studies was 0.99 for any night shift work, 1.01 for 20 or more years of night shifts and 1.00 for 30 or more years.

University of Oxford

Major review finds no cancer link to working nights

Ruth Travis

In other words, the incidence of breast cancer was essentially the same whether someone did no night shift work at all or did night shift work for several decades, said the researchers.

Lead study author Dr Ruth Travis said: “We found that women who had worked night shifts, including long-term night shifts, were not more likely to develop breast cancer, either in the three new UK studies or when we combined results from all 10 studies that had published relevant data.”

The research was funded by the Health and Safety Executive, Cancer Research UK and the Medical Research Council, and used the UK Biobank Resource.

Professor Andrew Curran, chief scientific adviser at the HSE, which commissioned the study, said: “Breast cancer is the most common cancer in women so it was vital for us to fund work in this area to establish if there is a link to night work.

He noted that two million UK women, about one in six female workers, currently worked some form of shift work, and over half a million of them were working in shifts that involved night work.

“This study has shown that night shift work, including long-term shift work, has little or no effect on breast cancer incidence in women,” said Professor Curran.

Health and Safety Executive

Major review finds no cancer link to working nights

Andrew Curran

”However, there are a number of other known risks with shift work that employers must take into consideration when protecting their workers’ health and safety,” he added.

Sarah Williams, Cancer Research UK’s health information manager, said: “This study is the largest of its kind and has found no link between breast cancer and working night shifts.

“Research over the past years suggesting there was a link has made big headlines, and we hope that today’s news reassures women who work night shifts,” she added.

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Readers' comments (1)

  • I think health more at risk when you are forced to work night shifts , or the other way around .if enough staff available and willing to do night shifts nobody should be forced.a happy workforce is a healthier workforce.a lot of nurses are leaving because they are bullied and threatened to do these shifts,when there is no need

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