The World Health Organization keeps an extensive list of possible and known human carcinogens that includes the usual suspects such as tobacco smoke, asbestos, UV radiation and processed deli meats and hotdogs.
But in 2007 the international public health agency added one surprising “probable carcinogen” to its ever-growing tally: night-shift work. Indeed, a mounting body of research connects working the graveyard shift and its associated circadian rhythm disruptions to a variety of negative health effects, including an increased risk of depression, obesity, cardiovascular disease, diabetes and cancer. And women may be particularly impacted: a new study finds that female nightshift workers have increased rates of nearly a dozen different cancers.
Some 20 percent of workers in industrialized nations work late-night or irregular shifts. That means millions of nurses, emergency room doctors, police officers, factory workers and airport personnel, among others, have a higher risk of developing a score of diseases.
And now a January 2018 meta-analysis of 61 studies with some 3.9 million participants from around the globe found that women who work the night shift have a 32 percent increase in breast cancer rates and a 19 percent increase in overall cancer risk. One group showed particularly striking results: Female nurses who worked the overnight shift had a 58 percent increased risk of developing breast cancer, according to the study, which was published in the journal Cancer Epidemiology, Biomarkers and Prevention.
While researchers are still investigating the possible links between shiftwork and cancers, the study authors speculated that one possible cause may be related to the strenuous nature of the job. Previous studies show that circadian disruption from nightshift work may cause hormonal changes that may boost the risk of cancer. Ddisruption to our body’s natural circadian rhythms over the long-term—say, years of clocking in for the overnight shift—has extensive effects on various body processes.
Ddisruption to our body’s natural circadian rhythms over the long-term—say, years of clocking in for the overnight shift—has extensive effects on various body processes.
Working Against the Body’s Natural Rhythms
We’ve all experienced the fatigue, confusion and general malaise associated with jet lag or pulling an all-nighter. The upside is that we generally return to normal within a few days. But disruption to our body’s natural circadian rhythms over the long-term — say, years of clocking in for the overnight shift — has extensive effects on various body processes. That’s because the body’s master clock, a cluster of neurons in the brain known as the superchiasmatic nucleus, sends signals to help keep essential processes running, from metabolism to hormone production. The master clock is regulated by light cues and other environmental factors. Nightshift workers, who are exposed to light throughout the night, can have disruption to these natural body rhythms.
Night-shift work has even been shown to impact our bodies at the epigenetic level. In other words, chronic disruption to circadian rhythms can result in changes to how our genes are expressed (translated from DNA to proteins). A Danish study of female nightshift workers found that long-term exposure to late-night work resulted in changes to genetic expression in two cancer-related genes. These alterations showed similar patterns to genetic changes seen in breast cancer patients, which may explain the shiftwork-breast cancer link, according the study’s authors.
As science continues to probe deeper into the workings of our body’s clock, we can better understand the true costs of burning the midnight oil.