Yet another study is linking night shift work with cancer.

French researchers from the Centre for research in Epidemiology and Population Health have have found that women who work the night shift have a 30 percent higher risk of breast cancer.

The risk was especially clear among women who did shift work for four years, as well as in those who only worked the night shift for three or fewer nights a week (since that meant their daily rhythms were disturbed more often).

The International Journal of Cancer study examined occupations of 1,200 women who developed breast cancer over a three-year period, and compared them with those of 1,300 other women. Of all the women, 11 percent worked nights at least once in their careers.

"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," study researcher Pascal Guenel said in a statement.

Last month, a study in the journal Occupational and Environmental Medicine also showed a link between shift work in women and breast cancer risk. HealthDay reported that breast cancer risk was highest among female shift workers who said that they are "morning people" instead of "night" people; a possible reason for this is the disruption of the body clock.

The Toronto Sun reported that the results of this study confirm the findings of the International Agency for Research on Cancer, which has a list of items and habits that may cause cancer. The IARC considers shift work "possibly carcinogenic."

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