Women who work night shifts are at a higher risk of developing breast cancer, French scientists announced after their research involving 2,500 women that were kept under observation for three years. Breast cancer is the leading cause of female mortality, annually affecting 100 women of 100,000 in developed countries. Each year, more than 1.3 million women are diagnosed with this disease. The risks are varied and include genetic mutations, older age at first pregnancy, severe hormonal disorders, nutrition, and lifestyle.
In 2010, International Agency for Research on Cancer has announced that circadian rhythm disturbances may have a carcinogenic effect. Circadian rhythm or body clock adjusts the alternation night – day, sleep – wake and controls many biological functions. In people who work at night or because of other various reasons can’t have the same program of rest every day, the circadian rhythm is altered. Experts have found the possible link between missed sleep at night and cancer risk: the exposure to light at night, which prevents the formation of melatonin (substance that has anticancer effects), dysfunction of genes that control cell proliferation, weakening the immune system.
French researchers examined the effects of artificial light at night on women’s health, a study conducted between 2005 and 2008. 2,500 women provided information on their careers, working hours and especially night hours worked. In total, over 11% of them have worked at night, at a certain time. The risk of developing breast cancer was found to be 30% higher in women who worked at night, compared with those who have never worked during the normal hours of sleep. Moreover, this risk was significantly higher in women who have missed sleeping at night for more than four years or those who work less than three nights a week, because this working schedule disrupts the alternation of night – day. More specifically, researchers found that the risk is higher in women who worked the night before the first pregnancy. The explanation is that cells in breast tissue that are not fully differentiated in women who have never given birth are more vulnerable.
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