Study Shines Light on Harmful Effects of Night Shift Work

Working a night shift may increase one’s chances of developing cancer, a new study finds, due to its effect on cell-destroying markers that remain in the body over time.

While previous research has linked night work to an increased risk of breast cancer, this new study, conducted by researchers at the Fred Hutchinson Cancer Research Center in Seattle, is the first to identify possible biomarkers deep within the body that signal cancer risk.

The researchers analyzed levels of the biomarker 8-hydroxydeoxyguanosine, or 8-OH-dG, in the urine of a group of 50 night shift workers. The biomarker is linked to the incidence of lesions, or harmful marks, on cells. Typically, the body is able to repair the lesions and excrete 8-OH-dG through the urine.

However, the researchers discovered that in night workers a smaller amount of 8-OH-dG was excreted through urine compared to regular daytime workers. That led the researchers to conclude that levels of 8-OH-dG were higher in nighttime workers, meaning that fewer lesions had been repaired.

When left unrepaired, “the 8-OH-dG lesions will cause mutations that can eventually lead to cancer,” according to the study.

The researchers believe that suppressed levels of melatonin, a hormone tied to sleep-wake cycles, are common in night shift workers and that lower amounts of circulating melatonin may be hindering cells’ ability to repair damage.

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The study casts further light on the potentially deleterious effects of regular sleep disruption and off-hours work.

“Shift work is a really complex exposure,” said lead researcher Dr. Parveen Bhatti, an epidemiologist with the Fred Hutchinson Cancer Research Center. “There’s light at night. There’s sleep disruption. There are different types of shift schedules that one can have.” 

The new study arrives in response to findings from 2016 that appeared to partially overturn previous links between night work and cancer. However, that study may have relied on subjective accounts of night shift work that skewed the outcomes, according to the current work.

To achieve a more granular assessment of night work, Bhatti and his colleagues decided to investigate physical changes in more of a real-time situation.

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“The studies that I have led are circumventing the use of historic data on shift work by looking at immediate biomarkers of effect,” Bhatti said. “Instead of looking at cancer as the endpoint, we look at a biomarker that we know is linked to cancer among current shift workers, like an oxidative DNA-damage marker.”

Bhatti says that the new evidence shows that the body’s naturally occurring defense mechanisms were essentially being overcome by a disruption to normal hormone levels, and the consequent halted release of the 8-OH-dG biomarker.

“The damage was done but it wasn’t repaired,” Bhatti said. “It’s sitting in their cells.”

Future studies will assess how melatonin supplements can impact cell repair, note the researchers. But in the meantime, those working at night should be especially careful about their health and well-being.

“It is even more critical for night shift workers to adhere to public health guidelines,” Bhatti said. “They should be sure to get enough sleep, eat a balanced diet and get plenty of exercise.”