In Summary
  • While overall long-term night shift work increased the risk of cancer by 19 percent, the risk of certain cancers were even higher.
  • Female night shift workers saw a 41 percent increased risk of skin cancer and a 32 percent higher risk of breast cancer.
  • The review incorporated 61 previously published studies on the topic, spanning 3.9 million participants from North America, Europe, Australia, and Asia and more than 110,000 cancers.

Women who regularly work the night shift in Europe and North America may face a 19 percent higher risk of cancer than those who work during the day, a study revealed on Monday.

These heightened risks were not apparent among female night-shift workers in Australia and Asia, said the meta-analysis in the journal Cancer Epidemiology, Biomarkers and Prevention.

SEX HORMONE LEVEL

"Our study indicates that night shift work serves as a risk factor for common cancers in women," said study author Xuelei Ma, an oncologist at the West China Medical Center of Sichuan University in Chengdu, China.

"We were surprised to see the association between night shift work and breast cancer risk only among women in North America and Europe," he added.

"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."

The review incorporated 61 previously published studies on the topic, spanning 3.9 million participants from North America, Europe, Australia, and Asia and more than 110,000 cancers.

One drawback to the study was that the different definitions of long-term night shift work — with some of the papers describing it as "working during the night" and others saying "working at least three nights per month." But the association was stark.

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