A study conducted by researchers at the French Inserm unit 1018 (Center for Research in Epidemiology and Population Health) and published in the International Journal of Cancer shows that the risk of developing breast cancer is higher among women who have worked at night.
The CECILE study, which was carried out in France, compared the careers of women who had developed breast cancer between 2005 and 2008 with the careers of other women.
The risk factors for breast cancer are varied and include genetic mutations, late first pregnancy, and hormonal therapy. There are also potential risk factors that have not been intensely studied, such as daily lifestyle (including professional lifestyle) and environmental factors.
The International Agency for Research on Cancer (IARC) has classified work that disturbs the circadian rhythm as a probable carcinogenic. Circadian rhythm regulates the alternation between wakefulness and sleep and controls numerous biological functions. That rhythm is altered in people who work at night or have disrupted working hours.
How will this increase the breast cancer risk? Several hypotheses have been proposed on why this may increase the risk:
- Exposure to light during the night eliminates the nocturnal melatonin surge and its anti-carcinogenic effects.
- The biological clock genes that control cell proliferation may be disturbed.
- Sleep disorders can weaken the immune system.
- Mammary cells, which are incompletely differentiated in women before their first pregnancy, may be more vulnerable in women who worked at night.
Inserm researchers examined the careers of 3,000 women in France, including each period of night work. Eleven percent of these women worked at night at some point in their career.
The risk of developing breast cancer was 30 percent higher in women who had worked nights than it was in women who had never worked nights. This risk appeared to be more significant in women who worked nights for more than four years or in women whose working rhythm was less than three nights per week, which leads to more frequent sleep pattern disturbance; twelve-hour night shift rotations come to mind.
When I read the Science Daily article on this study, I thought not only of the increased risk of breast cancer, but also the increased risk for other cancers, in women and men. I’m sure studies regarding circadian rhythm and cancer will take place soon enough.
For many of you, working during the night is your only option, because medical centers are 24-hour operations. What can we do to decrease the risk?
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Science Daily News.