Breast cancer is the type of cancer most common in women worldwide, both in developing countries and in developed countries. According to data from the National Cancer Institute (NCI), there will be more than 52,000 new women diagnosed in Brazil this year.
A risk factor that may be contributing to that number is night shift work, as pointed out by a new study published in the International Journal of Cancer.
In reaching this conclusion, a team from the Centre for Research in Epidemiology and Population Health (France), followed three thousand women for three years. Of the participants, 11% worked or had worked at night.
The results showed that the chance of developing breast cancer was 30% higher among women who worked or had worked nights, than those who had never worked at night. The risk proved to be even greater among participants who worked in varying shifts during the week, with at least one of them a night shift.
Another finding was the increased risk among women who had worked night shifts prior to their first pregnancy; the theory being that mammary cells may be more vulnerable at that time.
The study authors offered one possible explanation for this night shift effect as work at night disrupts the circadian rhythm; that is, the natural wake-sleep cycle that is innate in all humans. It regulates functions from digestion to the waking state and is essential for the proper functioning of the body. One suspects, therefore, that altering or stressing this natural cycle leads to malfunctions that could cause cancer.
Age remains a principal risk factor for breast cancer; the incidence increases with age. Other risk factors are well established, for example, those related to woman’s reproductive life (early menarche, never-pregnant women, age at first full-term pregnancy over 30 years, oral contraceptives, late menopause, and hormone replacement therapy), family history of breast cancer and high breast tissue density (ratio of the glandular tissue to fatty tissue in the breast).
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