The risk of breast cancer increases by 30% in women who work at night. This nocturnal activity disrupts the circadian rhythm, according to the Inserm study.
Night work is believed to be a risk factor for breast cancer, along with certain genetic mutations, late age at first pregnancy or even hormonal treatments. In any case, this is what Inserm researchers have just demonstrated in a large population survey on the impact of night work on women’s health carried out between 2005 and 2008.
The study called CECILE compared the professional career 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, in particular on populations of nurses, a link between night work and the risk of developing a breast tumor. This work, published in theInternational Journal of Cancer, therefore confirms these results and specifies them. The risk of breast cancer was increased by 30% in women who worked night shifts compared to those who worked during the day. In addition, this risk changes according to the duration and pace of work.
Pascal Guénel, main author of the Inserm study: “The risk is even higher in those whose work rhythm was less than 3 nights per week, with more frequent shifts in the day / night rhythm”
Finally, these researchers have shown for the first time that this risk of developing breast cancer was increased by 50% in women who started working at night, before having had a first pregnancy at term. The authors explain this phenomenon by the fact that, before a 1time pregnancy, mammary gland cells have not fully matured. And immature 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 breast cancers. Several hypotheses are put forward. The main one would be that night work disrupts the circadian rhythm, that is to say our internal clock, the one that manages the alternation of sleep-wakefulness.
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 day work without real regularity, this disorganization of the circadian rhythm can lead to disruption of the hormonal cycle.
Another lead is that people who work at night stay 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, the sleep disturbances often caused by these day / night rhythm changes could weaken the immune system.
The Inserm study revealed other surprises. The authors observed that 11% of women had worked nights at some point in their working life. A percentage which has been increasing since the law of May 9, 2001. In fact, until that date, night work for women was prohibited unless there was a 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 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.
Pascal Guénel: “It is not clear which type of night work is the most detrimental to health, but it could be a real public health problem. “
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