Working Nights May Increase Risk of Breast Cancer
It has long been thought that people who work night shifts are at risk for various conditions including sleep disorders, diabetes and heart disease. A recent study conducted in Denmark suggests that working nights may increase a woman’s risk of developing breast cancer.
The researchers gathered data on 18,500 women who worked for the Danish army between the years 1964 and 1999. From this group, 210 women who had breast cancer were compared against 900 women who did not have the disease. Study participants were asked about their working patterns and other lifestyle factors including their use of contraceptives and hormone replacement therapy, and their sunbathing habits. These women were also asked to classify themselves as either “morning” or “evening” people.
Among the survey respondents, it was found that women who worked night shifts had a 40% higher risk of developing breast cancer. Women who worked 3 night shifts each week for at least 6 years or more had double the risk of developing breast cancer compared to respondents who did not work at night. Women who categorized themselves as “morning people” and worked night shifts were at an even higher risk of developing breast cancer—4 times the risk of the participants who did not work night shifts.
Lead researcher Johnni Hansen, of the Institute of Cancer Epidemiology at the Danish Cancer Society, in Copenhagen, speculated on the results of this study. "Night shift work involves exposure to light at night, which decreases the production of the night hormone melatonin that seems to protect against certain cancers.”
Hansen also theorized that disturbances to a person’s circadian rhythms, a natural result of working nights, may have a role in the development of cancer. "Repeated phase shifting may lead to defects in the regulation of the circadian cell cycle, thus favoring uncontrolled growth," Hansen said. He also stated the stress of working nights may cause suboptimal performance of a person’s immune system, which can result increased growth of cancer cells.Continued on the next page