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Female night shift workers at increased risk for cancer
Long-term night shift work increased women’s risk for cancer by 19%, according to a study published in Cancer Epidemiology, Biomarkers & Prevention.
“Data from the third EU Survey (2000) showed that 76% [of] employees worked beyond normal working time. Up to 21.9% of men and 10.7% of women were exposed to shift work, with 7% [of the] population working permanently at night,” Xuelei Ma, PhD, of the West China Medical School and Sichuan University in China, and colleagues wrote. “Large numbers of people are being exposed to night shift work, which brings huge detrimental impact on health; it is, therefore, of much significance to conduct the study to illustrate the relationship between night shift work and the risks of frequently occurred cancers in women.”
Ma and colleagues conducted a meta-analysis of 61 articles from North America, Europe, Australia and Asia to determine associations between long-term night shift work and cancer risk. The articles consisted of 26 cohort studies, 24 case-control studies and 11 nested case-control studies that included 114,628 cancer cases and 3,909,152 participants.
Results showed female night shift workers had a 19% increased risk for cancer compared with those who did not perform long-term night shift work (OR = 1.19; 95% CI, 1.12-1.26).
Women who worked long-term night shift demonstrated an increased risk for skin cancer (OR = 1.4; 95% CI, 1.02-1.93), breast cancer (OR = 1.31; 95% CI, 1.19-1.44) and gastrointestinal cancer (OR = 1.17; 95% CI, 1.06-1.3).
Women who worked long-term night shift in North America (OR = 1.23; 95% CI, 1.04-1.45) and Europe (OR = 1.41; 95% CI, 1.24-1.61) had higher rates of breast cancer, whereas no correlations appeared among women in Asia (OR = 1.23; 95% CI, 0.85-1.27) and Australia (OR = 1.04; 95% CI, 0.85-1.27).
“We were surprised to see the association between night shift work and breast cancer risk only among women in North America and Europe,” Ma said in a press release. “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.”
Nurses who worked the night shift had a 57% increased risk for breast cancer (OR = 1.57; 95% CI, 1.23-2.01), a 35% increased risk for gastrointestinal cancer (OR = 1.35; 95% CI, 1.03-1.77) and a 28% increased risk for lung cancer (OR = 1.28; 95% CI, 1.07-1.53) compared with those who did not work night shifts.
Nurses had the highest risk for developing breast cancer if they worked the night shift compared with other analyzed occupations.
“Nurses who worked the night shift were of a medical background and may have been more likely to undergo screening examinations,” Ma said in the release. “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.”
Using studies that had at least three levels of exposure — most of which were studies of breast cancer — the researchers conducted a dose-response meta-analysis. Results showed for every 5 years of night shift work, the risk for breast cancer in women increased by 3.3% (OR = 1.03; 95% CI, 1.01-1.05).
The limitations of the study included inconsistencies between studies’ designs and definitions of “long-term” night shift work.
“Given the expanding prevalence of shift work worldwide and heavy public burden of cancers, 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 researchers wrote. “Also, in-depth biological [research] should be done to explore the mechanisms by which night shift work affects cancer risk.
“Knowing how night shift work serves as a risk factor for cancers might help establish and implement effective measures to protect female night shifters,” they added. “Moreover, it is important that long-term night shift workers accept regular physical examination and cancer screening for potential malignancies, particularly breast cancer.” – by Cassie Homer
Disclosures: The authors report no relevant financial disclosures.