Night Shifts Found to Increase Risk for Multiple Cancers in Female Nurses

By Mia Garchitorena
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A new international study found that night shift work significantly increases the risk of developing common cancers in women.

Researchers from West China Medical Center at Sichuan University in Chengdu, China, performed a meta-analysis to identify the potential risks of primary cancers in women, such as female nurses, following long-term night shift work. They found a possible relationship between long-term night shift work and the risks of several common cancers in women, according to the study. The study was published in Cancer Epidemiology, Biomarkers & Prevention.

Tired nurse. (Source: Shutterstock)

The researchers analyzed 61 articles involving 114,628 cases and nearly 4 million participants from Asia, Europe, North America, and Australia. According to the study, risk estimates were performed with a random-effect model or a fixed-effect model.

“By systematically integrating a multitude of previous data, we found that night shift work was positively associated with several common cancers in women,” said Xuelei Ma, PhD, oncologist at State Key Laboratory of Biotherapy and Cancer Center, West China Medical Center at Sichuan University and co-author of the study. “The results of this research suggest the need for health protection programs for long-term female night shift workers.”

The study found a positive association between long-term night shift work and risk of developing breast and skin cancer (41%) and cancers of the digestive system (18%). In Europe and North America, working the night shift was associated with a 32% increased risk for breast cancer (odds ratio, 1.316). The risk of breast cancer in women rose by 3.3% every five years of working the night shift (OR, 1.0333), the study stated.

“We were surprised to see the association between night shift work and breast cancer risk only among women in North America and Europe,” Dr. Ma said in a press release published by the American Association of Cancer Research (AACR). “It is possible that women in these locations have higher sex hormone levels, which have been positively associated with hormone-related cancers such as breast cancer.”

Female nurses that worked the night shift were found to have a 58% increased risk of developing breast cancer, a 35% risk of developing gastrointestinal cancer and a 28% risk of developing lung cancer compared with those who did not work night shifts. Dr. Ma told the AACR that these nurses may have had a higher risk of breast cancer because they were more likely to undergo screening since they were in a medical field. He also said that it may be related to intensive work environments.

“We identified that cancer risk of women increased with accumulating years of night shift work, which might help establish and implement effective measure to protect female night shifters,” the researchers said. Dr. Ma recommends that long-term, female night shift workers have regular physical exams and cancer screenings.

The authors stated that one of the study’s limitations was that there was an inconsistent definition of the word “long-term” night shift work, which could have been interpreted as working throughout the night or working “at least three nights per month”.