A study in China showed that night shift work is associated with an increased risk of women developing various cancers, especially breast, skin and stomach or intestine.
The researchers, led by the oncologist Sweley Ma of the Sichuan University Medical Center in Western China, published in the American Medical Journal “Cancer Epidemiology, Biomarkers & Prevention”, evaluated data from 61 investigations totaling approximately 3.9 million and 114,600 cancer cases in the US, Europe, Asia and Australia.
The conclusion of the data evaluation was that long-term shift work in the evening increases the risk of cancer among women by 19% on average, compared to those who do not work at night at all. With regard to individual types of cancer, the risk is more elevated for skin cancer (41%), breast (32%) and gastrointestinal (18%).
For reasons that are not clear, the increased risk of breast cancer concerns only night shift workers in the US and Europe, but not in other continents. One possible cause is that these women have elevated levels of hormones that promote cancer.
Of all occupations, nurses working on night shifts have the greatest risk of developing breast cancer. For nurses who work often in the evenings, the risk of breast cancer is increased by 58%, gastrointestinal by 35% and lungs by 28%.
The risk of breast cancer, according to the study, is increased by 3.3% for every additional five years of night work.