A meta-analysis published in January 2018 found that women who work night shifts may be at greater risk for several cancers. The risk for 11 cancers for long-term female night shift workers was analyzed with a focus on women in North America, Europe, Asia and Australia.
"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,” says Lead Author Xuelei Ma of the State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, West China Medical School, Sichuan University.
Previously, similar studies have focused solely on breast cancer risk for women who worked nights and had inconsistent results. Ma and his colleagues broadened their research to consider the risk levels for multiple cancers. They analyzed data from 61 articles containing 114,628 cases of cancer and 3,909,152 participants. A total of 24 case-control studies, 26 cohort studies and 11 nested case-control studies were included. They also conducted an inquiry specifically into the connection between night work over an extended period for female nurses and six types of cancer.
Long-term nightshift work was found to increase cancer risk for the women by 19 percent overall. Specific findings included: skin cancer: 41 percent, gastrointestinal: 18 percent, and breast: 32 percent. A surprising finding was that an uptick in breast cancer risk was only discerned among female night shift workers in Europe and North America. Ma felt this may have been due to differences in “sex hormone levels, which have been positively associated with hormone-related cancers such as breast cancer,” between the women in these locations.
For female nurses, those on the night shift had a 58 percent increase in breast cancer risk, a 35 percent increase for gastrointestinal, and a 28 percent increase for lung cancer. Out of all of the various careers included in this analysis, night shift nurses had the highest breast cancer risk. Ma said the intensive workload for these positions might account for this, as might the women’s possible increased likelihood to seek screenings as employees of a healthcare facility.
Finally, this team of scientists analyzed how breast cancer risk might change over time. They report that the risk increases 3.3 percent with every five years of night work.
Ma says shift work has an “expanding prevalence” around the world and that cancers come with a “heavy public burden.” So, he hopes this meta-analysis will bring more attention to the dangers female night workers face and inspire additional related studies into the associations he and his team discovered.
“Long-term night shift workers should have regular physical examinations and cancer screenings,” he concludes.
