Study reveals increased risk of common cancers among female night shift workers

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Jan 8 2018

A new study published in the journal of American Association for Cancer Research, Cancer Epidemiology, Biomarkers & Prevention, has revealed the increased risk of breast, skin, and gastrointestinal cancers among women who work night shifts.

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Researchers at State Key Laboratory of Biotherapy and Cancer Center, West China Medical Center of Sichuan University carried out a meta-analysis using 61 articles, which comprised the details of 114,628 cancer cases and 3,909,152 participants from North America, Europe, Australia, and Asia.

The articles comprised of 24 case-control studies, 26 cohort studies, and 11 nested case-control studies, which were analyzed for an association between long-term night shift work and the risk of 11 types of cancer. Further analyses were performed specifically to observe the link between long-term night shift work and the risk of six types of cancers among female nurses.

The study findings showed elevated cancer risk by 19% in female night shift workers. When examining for specific cancers, researchers found an increased risk of breast, skin, and gastrointestinal cancers by 32%, 41%, and 18%, respectively, among female night shift workers compared to that of other female employees who did not perform night shifts. After classifying the participants by their location, scientists discovered that an increased breast cancer risk only found among female night shift workers in North America and Europe.

Among female nurses alone, those who worked the night shift had an increased risk of breast (58 percent), gastrointestinal (35 percent), and lung cancer (28 percent) compared with those that did not work night shifts.

According to Dr. Xuelei Ma, the lead author and oncologist at State Key Laboratory of Biotherapy and Cancer Center, West China Medical Center of Sichuan University, breast cancer is the most diagnosed cancer among women globally. Therefore, the majority of prior meta-analyses focused on realizing the link between female night shift workers and breast cancer risk, but the results have been inconsistent.

To contribute to previous studies, Ma and colleagues studied whether long-term night shift work in women was associated with risk for almost a dozen types of cancers.

The scientists also carried out a dose-response meta-analysis among breast cancer studies which involved three or more levels of exposure. They observed that the risk of breast cancer heightened by 3.3% for every five years of night shift work.

By systematically integrating a multitude of previous data, we found that night shift work was positively associated with several common cancers in women. The results of this research suggest the need for health protection programs for long-term female night shift workers.”

Dr. Xuelei Ma, West China Medical Center of Sichuan University

According to the study, one of the risk factors for common cancers in women is working night shifts. The findings of the study are expected to help establish and implement effective measures to protect female night shifters. It suggests that long-term female night shift workers undergo regular physical examinations and cancer screenings.

"Given the expanding prevalence of shift work worldwide and the heavy public burden of cancers, we initiated this study to draw public attention to this issue so that more large-cohort studies will be conducted to confirm these associations," he added.

The lack of consistency between studies regarding the definition of "long-term" night shift work, with definitions including "working during the night" and "working at least three nights per month.” Is a limitation of this study. Significant between-study heterogeneity and publication bias are additional study limitations.