Women who work the night shift have increased odds of developing breast, skin, and gastrointestinal cancer, a new meta-analysis shows. Nurses working night shifts seem to be at even higher risk of developing cancer.
The study, “Night Shift Work Increases the Risks of Multiple Primary Cancers in Women: A Systematic Review and Meta-analysis of 61 Articles,” was published in the journal Cancer Epidemiology, Biomarkers & Prevention.
Over the years, rates of breast cancer have been going up faster in industrialized regions than in developing countries. It is now the most common cancer in women worldwide. This suggests that women’s lifestyle in modern society also plays a role in cancer development.
At the same time, the number of women working night shifts is increasing, particularly in the nursing group. The World Health Organization has classified shift work as probably carcinogenic (meaning it promotes cancer) due to disruption of normal sleep routines.
Although several studies have examined the association of night shift work with cancer development, no consensus has yet been reached.
Now, a Chinese team of researchers at State Key Laboratory of Biotherapy and Cancer Center performed a meta-analysis to analyse the effect of night shift work on the risk of 11 types of cancer among women.
The meta-analysis used data from 61 studies, which included more than 3.9 million participants and 114,628 cases of cancer from North America, Asia, Europe, and Australia.
Long-term night shift work was found to increase the overall risk of cancer in women by 19%. These women had a significantly increased risk of skin (40%), breast (31%), and digestive system (17%) cancer, compared to those who did not work night shifts.
The risk of breast cancer in women was found to increase 3.3% for every five years of night shift work. But looking at the geographical location, researchers were surprised to see that only North American and European women working night shifts were associated with higher risk of breast cancer.
“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,” Dr. Xuelei Ma, PhD, the study’s senior author, said in a press release.
When comparing women’s occupations, the study found that night shift nurses had the strongest risk of breast cancer (58%). They also had increased risk of gastrointestinal (35%), and lung (28%) cancer.
“Nurses that worked the night shift were of a medical background and may have been more likely to undergo screening examinations,” said Ma. “Another possible explanation for the increased cancer risk in this population may relate to the job requirements of night shift nursing, such as more intensive shifts.”
Ma noted that the results “might help establish and implement effective measures to protect female night shifters. Long-term night shift workers should have regular physical examinations and cancer screenings.”
However, the team pointed out that their analysis had some limitations due to the inconsistent definition of “long-term” night shift work, heterogeneity, and publication bias.
“Further research, particularly large-size, high-score cohort studies are of great necessity to confirm the relationship between night shift work and cancer risk,” the team concluded.
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