Working at night does not raise risk of breast cancer
night shifts do not increase a woman’s risk of breast cancer, Oxford scientists say.
their research, based on data from 1.4million women, casts doubt on earlier studies showing a link.
the latest findings combine the results of three new UK-based studies with seven studies from the US, China, Sweden and the netherlands.
Researchers found that neither women who had worked night shifts for at least one period in their lives, nor women who had worked nights for 20 or 30 years had any increased risk of developing breast cancer.
‘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 ten studies that had published relevant data,’ said Ruth travis, of the cancer epidemiology unit at the University of Oxford.
On average, one in seven women in the UK work nights at some point in their lives, with one in 50 doing so for 20 or more years.
the researchers in the latest study, published in the Journal of the national Cancer institute, found the proportion of women who developed breast cancer was virtually the same regardless of whether they did no night shift work or if they had worked nights for decades.
Previous research published in 2007 by the World health Organisation’s international Agency for Research on Cancer said shift work disrupted the body clock and this could cause cancer.
At the time there was limited evidence about breast cancer risk in humans so the conclusions were mainly based on a combination of animal and laboratory studies.
Sarah Williams, of Cancer Research UK, 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.’
Professor Andrew Curran, chief scientific adviser for the health and Safety Executive, which commissioned the study, said around half a million British women worked night shifts.
he added: ‘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. this study has shown that night shift work, including long-term shift work, has little or no effect on breast cancer incidence in women.
‘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.’
Previous studies have shown working night shifts puts a strain on health, with night workers as much as 40 per cent more likely to suffer a heart attack or stroke.
And researchers from Stanford University School of Medicine in the US found that women living in areas with the brightest outdoor light at night ‘may be at an increased risk of breast cancer’. the study did not establish a causal link but suggested a connection with disrupted body clocks.
Each year 53,300 women are diagnosed with breast cancer and around 11,500 die from it.
‘Largest study of its kind’