Women who work overnight are increasing their risk of breast cancer © RexWomen who work overnight could be putting their health at risk, according to a new study by the Centre for research in Epidemiology and Population Health.
The study, carried out in France between 2005 and 2008, compared the careers of 1,200 women who had developed breast cancer and 1,300 women who hadn’t. Overall, 11 per cent of the women had worked night shifts during their career.
The risk of developing breast cancer was 30 per cent higher in women who had worked night shifts, compared to women who had never worked at night. This increased risk was especially marked in women who had worked night shifts for more than four years, though women who worked less than three night shifts are week were also found to be more likely to develop breast cancer.
The researchers believe this may be because the shift work disturbs our natural night/day rhythms, affecting the production of the sleep hormone melatonin, which is thought to have anti-cancer properties.
The occupations considered most risky by the study were nurses and flight attendants but with an increasingly 24/7 culture, more and more of the population is involved in some sort of shift work.
The study also found that the risk increased in women who had worked night shifts before their first pregnancy, as their mammary cells are more vulnerable at this stage.
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Pascal Guénel, the main author of the study, said: “Our work has corroborated the results of previous studies and poses the problem of taking night work into consideration in public health management, especially since the number of women working atypical hours is on the increase.”
The study attributed night work to around 550 deaths from breast cancer in the UK each year. Breast cancer is the number one cause of female mortality worldwide. It affects 0.1 per cent of women in developed countries, and 1.3 million new cases are diagnosed each year.
Other risk factors vary, but include genetic mutations, late first pregnancy, having few children and undergoing hormone therapy.