Trial sheds less light on nurses working night shift

Improved job performance, quality of sleep

The potential downsides to shift work are increasingly being publicized — sleep disturbance, risk of injury, reduced productivity and more serious health concerns such as cancer and cardiovascular disease. What’s less understood is the actual reason behind the occupational hazards. What exactly is it about shift work that causes the problems?

Nurses at Western Toronto Hospital were treated to a first-hand look last year when they participated in a field trial to test special glasses during night shifts. The filters block light in the 470 to 480 nanometre range, which is thought to be the wavelength that suppresses melatonin (a hormone secreted at night that maintains the body’s circadian rhythm and may act indirectly or directly in causing cancer), said Robert Casper, a senior scientist at the Samuel Lunenfeld Research Institute at Mount Sinai Hospital in Toronto who was involved with the trial.

There are 1,500 genes in the body that have a 24-hour rhythm and all of these are disrupted by inappropriate light exposure at night, which could be related to obesity, insulin activity or cancer, he said. The glasses can restore melatonin secretion, while also preventing a rise in cortisol, a stress hormone that is normally low at night but rises in the day, he said.

“We think of it as a potential way to prevent cancer in the future,” said Casper.

The results of the trial at Toronto Western appear impressive: Salivary samples taken at regular intervals revealed a partial suppression of melatonin levels and a shift in the peak of melatonin secretion from 12:00 a.m. to 6 a.m. The amount of sleep and quality of sleep after the night shifts also improved, as did the nurses’ memory and performance on the job.

Usually they would get about six hours of sleep per night, waking for about 100 minutes during the night. But with the filters, the nurses slept 80 minutes longer at Toronto Western’s sleep lab and woke only 25 minutes. They also fell asleep in seven minutes, not the usual 15 minutes.

“Quality of or sleep efficiency increased to 88 per cent from 70 per cent,” said Casper, who is also a professor in reproductive sciences at the University of Toronto.

Through subjective mood scales, the nurses said the glasses also improved their mood and reduced anger and anxiety while working and improved response time on the night shift, he said.

As a result, the hospital is now looking into a larger, more involved study.

“It’s really taken off,” said Mary Jane McNally, director of nursing at Toronto Western Hospital. “We have some great interest in extending the research project so we can have a better sense of how potentially use of the filter or glasses would really impact things like our absenteeism rates, our workplace injuries, turnover, along with some long-term impact in terms of the health and well-being of our nursing staff.”

The challenges of shift work — such as fatigue and lack of alertness — have been a frequent topic at the hospital for years, she said, and it was eye-opening to hear the trial researchers say shift work is life-threatening and a probable carcinogen.

There’s a wide array of health effects associated with shift work and varying degrees of evidence in terms of some of the more serious impacts, said Paul Demers, director of the Occupational Cancer Research Centre in Toronto.

“They’re finding a lot of different processes in the body are what we would call clock-controlled, so they’re attached to circadian rhythms, and there’s a recognition now that that has an impact on a lot of different hormones, it has an impact on the immune system, it has other impacts that are certainly things that would raise concern,” he said.

To mitigate these harmful impacts, several preventive measures are being considered, ranging from changing lighting patterns at night, changing shift times, shorter night shifts or giving people melatonin pills, said Demers.

“People are looking to find solutions that don’t involve the elimination of shift work altogether but might reduce some of the more extreme effects,” he said.

Toronto Western has set up a working committee with its HR, health and safety and risk management departments and the researchers to look at what sort of metrics it wants to evaluate going forward.

“There’s great interest on the part of the organization to explore ‘What evidence do we need to actually invest in these filters or glasses?’” said McNally. “The investment would be a certain amount of money upfront but that would be mitigated by the long-term savings where we have staff more present at work physically, less absenteeism, but also more vigilant, more alert, more responsive (staff) and, ultimately, less health-care costs in terms of these significant diseases.”

Bruce Power in Tiverton, Ont., also did a field trial with the glasses and subjective sleep diaries showed the same results, said Casper. He is now in discussions with General Motors to do a possible field study at one of its plants in Ontario that has a non-rotating shift that involves people who permanently work nights, with weekends off.

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