Night-shift link to breast cancer is disputed

NIGHT shifts do not increase the likelihood of developing breast cancer, despite previous evidence to the contrary, a study has found.

The research, published in the British Journal of Cancer, found women who worked overnight were no more likely to develop the disease than those who worked regular hours.

The findings will provide reassurance to thousands of workers, following decades of debate over the link between night shifts and breast cancer.

It was first suggested in the Seventies that exposure to electric light may increase the risk of developing the disease, by potentially disrupting the body’s internal clock, suppressing levels of the sleep hormone melatonin and raising oestrogen levels.

In 2007, the International Agency for Research on Cancer, part of the World Health Organisation, said that shift work that disrupts the sleep cycle is “probably carcinogenic”.

The latest study, funded by the charity Breast Cancer Now, included data from 102,869 UK women over 10 years, 2,059 of whom went on to develop invasive breast cancer.

Analysis by the researchers found no overall link between night shift work and the likelihood of developing breast cancer.

“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,” said Dr Michael Jones, who led the research at the Institute of Cancer Research in London (ICR).

“In our study, we found no overall link between women having done night shift work in the last 10 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 International Agency for Research on Cancer, which forms part of the World Health Organisation, is set to review evidence on night shift work and cancer this summer.

Baroness Morgan of Drefelin, 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.”