Women who did night shifts had a higher risk of developing breast cancer, as compared to sisters who worked in daytime, according to a study.
"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 a typical hours is on the increase," states Pascal Guenel, of Inserm (Institut National de la Sante et de la Recherche Medicale), who led the study.
Breast cancer is the number one cause of female mortality. It affects 100 out of 100,000 women per year in developed countries. Every year, more than 1.3 million new cases are diagnosed, 53,000 of these in France, said a university statement.
Inserm researchers examined the effect of night work on the health of 3,000 women in France between 2005 and 2008, including each period of night work. Over 11 percent of women had worked nights at some time during their career.
This increased risk was particularly marked in women who had worked nights for over four years, or in women whose working rhythm was less than three nights per week, because this led to more frequent disturbances between night and day rhythms.
Finally, the link between night work and breast cancer seemed to be more marked when we looked at women who had worked at night prior to a first pregnancy.
An explanation for this result could be that the mammary cells, incompletely differentiated in women before their first pregnancy, are more vulnerable.