Night work a Health Risk for Women
A study carried out by researchers at the Centre for Research in Epidemiology and Population Health in France, and published in the International Journal of Cancer , suggests that the risk of developing breast cancer is higher among women who have worked at night. The study compared 1200 women who had developed breast cancer between 2005 and 2008 with 1300 other women.
Breast cancer is the number one cause of female mortality, affecting 1 in 1000 women per year in developed countries. Each year, more than 1.3 million new cases are diagnosed. The risk factors are varied and include genetic mutations, late first pregnancy, low parity or hormone therapy, but other factors such as lifestyle and occupational practices are not yet fully understood.
In 2010, the International Agency for Research on Cancer (IARC) classified work that disturbed the circadian rhythm (or body clock) as being “probably carcinogenic.” 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 the increased prevalence of sleep disorders amongst night shiftworkers, that can weaken the immune system.
The study found that the risk of developing breast cancer was 30% higher in women who had worked nights, and that the increase in risk was particularly marked in women who had worked nights for over four years. The link between night work and breast cancer also appeared stronger in women who had worked at night prior to a first pregnancy. One explanation for this result could be that the mammary cells, incompletely differentiated in women before their first pregnancy, are more vulnerable.
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