Cancer risk linked to night shifts, study finds

Working night shifts for more than 30 years could double women’s risk of developing breast cancer, research suggests.

Nurses, cleaners, care workers, some shop workers, call centre handlers and others who work night shifts for a long term can have a twice as high risk of developing the disease than those who don’t, the study found.

Canadian researchers examined 1,134 women with breast cancer and 1,179 women without the disease, but of the same age. Women were questioned about their work and shift patterns and researchers also assessed the hospital records for the women who suffered from the disease. About a third of the women had a history of night shift work.

The study, published in Occupational and Environmental Medicine, found that those who had worked nights for 30 or more years were twice as likely to have developed the disease, after taking account of potentially influential factors, although the numbers in this group were comparatively small.

No such relationship was found if women worked for less than 30 years doing shift work.

Previous research has linked the disease with shift work done by nurses, but the latest study found that the associations were similar among those who worked in healthcare and those who did not.

“An association between more than 30 years of night shift work in diverse occupations and breast cancer is supported here, consistent with other studies among nurses,” the authors said. “As shift work is necessary for many occupations, understanding of which specific shift patterns increase breast cancer risk, and how night shift work influences the pathway to breast cancer is needed for the development of healthy workplace policy.”

But experts urge caution.

Dr Jane Green, at the University of Oxford, said: “This seems to be a well-conducted study with the benefit of more detailed occupational history than in many studies. The finding of an increased risk of breast cancer in women with a long history of shift work adds to similar results from some previous studies, but does not change the existing consensus: that, while there is some evidence to associate increased risk of breast cancer with very long-term shift work, the evidence is not yet sufficient to be sure and certainly not sufficient to give a public health message about working shifts.”

Dr Hannah Bridges, senior information officer at the charity Breakthrough Breast Cancer, added: “This is one of a few studies that suggest working night shifts for many years may increase breast cancer risk. However, we don’t yet know that shift work is a risk factor for breast cancer, so we’d urge women not to panic.”


Lifestyle

The long-tailed tit’s nest is an architectural marvel.Richard Collins: Altruism of the long-tailed tits or not

The flight that brought us home to Ireland after our seven months sojourn in the Canary Islands (half our stay intended, half not) was the most comfortable I’ve experienced in years. With a large plane almost entirely to yourself, you could again pretend you were somebody.Damien Enright: Wonderful to see the green, green grass of home

IRISH folklore is replete with stories of priests praying for fine weather to help farmers save their crops in wet summers. However, the opposite could soon be happening when divine powers may have to be invoked to provide rain. And not just for farmers.Donal Hickey: Praying for rain — in Ireland

Geography is often the defining factor for the destiny of an island. Those islands that lie close to the shore have often been snapped up by interests on the mainland and their morphology changed to something completely different.The Islands of Ireland: Tarbert morphed onto the mainland

More From The Irish Examiner