The study named CECILE compared the course professional of 3000 women. Of these, 1,200 had had breast cancer during this period and 1,300 had not had this disease.
Previous studies had already shown, particularly on nurses’ populations, a link between night work and the risk of developing a breast tumor. This work, published in the International Journal of Cancer, confirms these results and specifies them. The risk of breast cancer was increased by 30% for women who worked at night compared to those who had been working in the daytime. Moreover, this risk evolves according to the duration and pace of work.
Finally, these researchers showed for the first time that this risk of breast cancer was increased by 50% among women who started working at night, before having had a first full-term pregnancy. The authors explain this phenomenon by the fact that, before 1 st pregnancy, cells of the mammary gland is not fully reached maturity. And non-mature cells are more vulnerable to external carcinogenic effects.
Another indication, it is not the night work in itself or its arduousness which would be at the origin of these cancers of the breast. Several hypotheses are advanced. The main thing is that night work causes disruption of the circadian rhythm, that is to say, our internal clock, which manages sleep-wake alternation.
A clock that regulates several biological functions of the body. For example, in women with a very changeable day / night rhythm, alternating night work and daytime work without real regularity, this disorganization of the circadian rhythm can lead to disturbances of the hormonal cycle.
Another track, individuals who work at night remain exposed to light longer, which reduces the secretion of melatonin. This sleep hormone, normally stimulated in the absence of light, is known for its anti-carcinogenic effects. Finally, sleep disturbances often caused by these changes in day / night rhythm could weaken the immune system.
The Inserm study revealed other surprises. The authors observed that 11% of women had worked at night at some point in their working lives. A percentage that is increasing since the law of 9 May 2001. Indeed, until that date, night work of women was prohibited except derogation.
But men who work at night also put their health at risk. Several studies have already been published or are in progress and are interested in the subject. Some of them are working on the impact of night work on prostate cancer. According to Pascal Guénel, the first results would go in the same direction, that is to say towards an increased risk of prostate cancer.
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