The results of a study carried out by the researchers of the Inserm unit 1018 (Centre for research in Epidemiology and Population Health) and published in the International Journal of Cancer show that the risk of developing breast cancer is higher among women who have worked at night.
The study, carried out in France and named the CECILE study, compared the careers of 1200 women who had developed breast cancer between 2005 and 2008 with the careers of 1300 other women.
Breast cancer is the number one cause of female mortality. It affects 100 out of 100,000 women per year in developed countries. Each year, more than 1.3 million new cases are diagnosed, 53,000 of these in France.
The risk factors of breast cancer are varied. They include genetic mutations, late first pregnancy, low parity or hormone therapy, but other causes of breast cancer such as way of life, environmental or professional causes have not yet been completely identified. In 2010, based on experimental and epidemiological work, the International Agency for Research on Cancer (IARC) classified work that disturbed the circadian rhythm as being "probably carcinogenic." The circadian rhythm, that regulates the alternation between wakefulness and sleep, controls numerous biological functions and is altered in people who work at night or who have disrupted working hours. Several hypotheses have been put forward to explain the observed links between night work and breast cancer: exposure to light during the night, that eliminates the nocturnal melatonin surge and its anti-carcinogenic effects, disturbed functioning of the biological clock genes that control cell proliferation, or sleep disorders that can weaken the immune system.