(MintPress) – A new study out of Denmark published in the Occupational and Environmental Medicine journal suggests that women who work night shifts are at a 40 percent increased risk of breast cancer. Those who work full-time shifts at night have long been studied for adverse health effects, which many say puts their safety at risk on the job.
In the study, it was discovered that those who had worked at least three nights a week for six years were more than twice as likely to be afflicted with breast cancer as those who did not work the shifts.
In the United States, nearly 15 million Americans work a permanent night shift or rotate in and out of night shifts, according to the American Psychological Association (APA). In 2007, the World Health Organization (WHO) said overnight shift work was a “probable” cancer-causing variable.
In an interview with The Daily at the University of Washington, UW chairman of epidemiology Scott Davis said studies have produced a long list of health effects that result in disrupting circadian rhythm – the body’s biological clock that regulates daily rhythms such as sleep in many living organisms.
“These include increased gastrointestinal disorders, increased stress, perhaps an increase in some cardiovascular diseases, perhaps some increase in adverse pregnancy outcomes, and an increase in breast, prostate, colon and endometrial cancer,” Davis said. “All of these cancer types are thought to be related to hormone levels.”
The APA describes circadian rhythm as “a timer that lets various glands know when to release hormones and also controls mood, alertness, body temperature and other aspects of the body’s daily cycle.”
Disruption in those rhythms can suppress production levels of melatonin, the hormone responsible for regulating the sleep-wake cycle in humans. Melatonin, normally produced in the body at night, has also been shown to reduce the risks of tumor development.
In 2009, researchers found that shift work – any schedule that falls outside the nine-to-five realm – could contribute to diabetes and heart disease. In a study that tracked subjects for 10 days and required them to sleep and work at different parts of the day for the study, all of the subjects saw a decrease in levels of weight-regulating hormones and drastic changes in blood sugar.
The study showed that three of the subjects tested, while healthy before the study, developed glucose levels that would qualify them as pre-diabetics if the levels were maintained for a consistent amount of time.
“Our internal biological clocks represent a whole area of biology that is as critical as blood pressure or breathing,” said Joseph Bass, an assistant professor of medicine at Northwestern University’s Feinberg School of Medicine in Chicago in an interview with Health.com. “And this work does provide us with a plausible biological mechanism that may underlie and cumulatively contribute to the occurrence of metabolic disorders in certain individuals, because of their work patterns, or because of traveling, or simply because they ignore the normal light cycle.”
Shift work sleep disorder
Much of the work that requires night shift status come from public services and demand high levels of precision. The risk of shift work sleep disorder – a condition characterized by insomnia and excessive sleepiness – runs high in professions such as overnight hospital workers, police officers, firefighters and factory workers. Aside from being a health threat, however, doctors say it is a threat to cognition and can be a serious safety threat on the job.
Characterized by impaired memory and focus, as well as mood swings, for a person on the job, such as a surgeon or pilot, their fatigue can be life-threatening to others. A 2010 study in the New England Journal of Medicine found that mistakes made by surgeons – who often are on-call throughout the night – are often attributed to fatigue-related issues.
ABC News reported that when the study looked at the performance of surgeons who worked on less than six hours of sleep, there was an increased risk of bleeding and organ damage during the procedures.
«We have data that show that sleep deprivation affects clinical performance, and we also have data that show that patients want to be informed if their surgeon didn’t get enough sleep, so it’s become a patient advocacy and safety issue,» said Dr. Michael Nurok, lead author of the article.
Last spring, various instances saw air traffic controllers fall asleep on the job due to their schedule. One controller said he was exhausted after rotating shifts, putting him on four consecutive overnight shifts when he was not a regular overnight worker.
Exhaustion has also impacted the transportation sector, as airline pilots and train operators have said lack of sleep has influenced their job performance. In March, researchers found that 20 percent of pilots admitted to making a serious error while flying due to sleepiness. Similarly, 18 percent of train operators and 14 percent of over the road truck drivers admitted to incidents related to sleep deprivation.
While risks occur on the job for those in transportation, many say they feel they are a greater risk while on the road driving home from a long shift. Drowsiness plays an exponentially greater role in car crashes from those in the transportation sector than those who are not, according to Dr. Sanjay Patel, a sleep researcher at Brigham and Women’s Hospital and Harvard Medical School.
«Driving home from work after a long shift is associated with crashes due to sleepiness,» Patel said in an interview with UPI. «We should all be concerned that pilots and train operators report car crashes due to sleepiness at a rate that is six times greater than that of other workers.»
Shift work is a common employer practice around the world. In China’s heavy manufacturing industry, 36 percent of employees’work varied and overnight shifts, according to the International Labour Organization (ILO).
The group points out that the type of industry in a country can also drive demand for shift workers. In Jamaica, a country that relies mostly on transport and hospitality, an average of 84 percent of workers in the country are on a shift work schedule. Contrary to Jamaica, only 14 percent of employees in the United Kingdom are regular shift work employees.