Study Finds Increased Risk in Common Cancers in Female Night Shift Workers

Key Points

  • Overall, long-term night shift work among women increased their risk of cancer by 19%. For specific cancers, this population had an increased risk of skin (41%); breast (32%); and gastrointestinal (18%) cancers compared to women who were not long-term night shift workers.
  • The increased risk of breast cancer was only found among female shift workers in North America and Europe.
  • The cancer risk of these workers increased with accumulating years of night shift work, which might help establish and implement effective measures to protect female night shift workers.

In 2007, the International Agency for Research on Cancer classified shift work with circadian disruption or chronodisruption as a probable human carcinogen. Now, a meta-analysis investigating whether long-term shift work increases the risks of common cancers in women has found that, overall, night shift work increased the risk of cancer by 19%, especially breast, skin, and gastrointestinal cancers in these workers, compared to women who did not perform long-term night shift work. The study’s results suggest the need to establish and implement effective measures to protect female night shift workers. The study by Yuan et al is published in Cancer Epidemiology, Biomarkers, & Prevention.

Study Methodology

The researchers analyzed 61 articles involving 114,628 cases and 3,909,152 participants from Europe, North America, Asia, and Australia. They used the Newcastle-Ottawa Quality Assessment Scale for quality evaluation of the eligible studies and evaluated the association between night shift work and female cancer risk using statistical software STATA version 11.0.

The studies were analyzed for an association between long-term night shift work and the risk of 11 types of cancer. A further analysis examined long-term night shift work and the risk of six types of cancer among female nurses.

Study Findings

The researchers found a positive relationship between long-term night shift work and the risks of breast cancer (odds ratio [OR] = 1.316; 95% confidence interval [CI] = 1.196–1.448], digestive system (OR = 1.177; 95% CI = 1.065–1.301), and skin cancer (OR =1.408; 95% CI = 1.024–1.934). In addition, for every 5 years of night shift work, the risk of breast cancer in women was increased by 3.3% (OR = 1.033; 95% CI = 1.012–1.056).

Concerning the group of nurses, long-term night shift work presented potential carcinogenic effect in breast cancer (OR = 1.577; 95% CI = 1.235–2.014), digestive system cancer (OR = 1.350; 95% CI = 1.030–1.770), and lung cancer (OR = 1.280; 95% CI = 1070–1.531).

“Given the expanding prevalence of shift work worldwide and heavy public burden of cancers, further researches, particularly large-size, high-score cohort studies are of great necessity to confirm the relationship between night shift work and cancer risk. Also, in-depth biological researches 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,” concluded the study authors.

Xuelei Ma, PhD, of the West China Medical School of Sichuan University in Chengdu, China, is the corresponding author of this study.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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