Shift work presents many health dangers: Symposium

More research needed to mitigate negative effects

Evidence is mounting linking shift work to cancer, cardiovascular disease, workplace injuries and pregnancy complications.

But there still needs to be more research into how shift work affects health and how employers can mitigate the negative effects, according to Ron Saunders, a senior scientist at the Institute for Work and Health, which hosted a scientific symposium on the health effects of shift work in Toronto in April.

“We know enough to be concerned about the potential effects of shift work on health,” he said. “The research so far leaves us with quite a bit of uncertainty about how big those health impacts are.”

Strong link between shift work, breast cancer

The strongest evidence is for the link between shift work and cancer, especially breast cancer, said Aaron Blair, an interim director at the Occupational Cancer Research Centre in Toronto.

There is slightly weaker evidence linking shift work to prostate cancer and even weaker evidence linking shift work to ovarian, endometrial and colon cancers, he said.

In 2007, night work was classified as a probable carcinogen — on par with ultraviolet rays — by the World Health Organization’s International Agency for Research on Cancer.

“The amount of information available is not at the level of, for example, tobacco smoking and lung cancer or radiation and lung cancer or arsenic and bladder cancer, but it’s pretty strong,” said Blair.

While there’s also evidence workplace injuries and sleep disruption are more likely among shift workers than regular day workers, there is only limited evidence linking shift work to cardiovascular disease and low birth weight, said Saunders.

Exposure to light main culprit

The main culprit of shift work appears to be a worker’s exposure to light during a normally dark period, but exactly how that exposure might cause cancer is unknown, said Blair.

There are several theories, the strongest of which is a disruption in the production of melatonin, which is produced at night and involved in hormonal function. And hormones play a role in all of the cancers linked to shift work, he said.

Another theory is shift work interferes with the immune system, making it less effective at monitoring and killing rogue cells that could develop into cancerous tumours, he said. Researchers are also looking into the possibility exposure to light causes mutations in the clock genes — the genes that synchronize the body’s sleep and wake cycles.

Another possible cause for the negative health effects include vitamin D deficiency due to less exposure to the sun, said Saunders.

“We need more work to understand better which are the key mechanisms that are at work here around health effects,” he said.

There also needs to be more research into why some workers are more vulnerable to the negative effects of shift work and what kind of shift work, precisely, is to blame, said Saunders.

“We need to try to measure the exposure to shift work more carefully,” he said.

The symposium didn’t address how to mitigate the negative health effects of shift work, said Saunders, but this is definitely an area for future discussion.

Some of the studies suggest it’s not just light in general that has a negative effect but certain wavelengths. If research can show which wavelengths are to blame, workers could wear lenses that block those wavelengths, said Blair.

There is also the possibility rotating shift work has the most deleterious effect. It might be better for employees to work the night shift for a longer period of time rather than to keep going back and forth between day and night shifts, he said.

“Cycling people is probably not a good thing,” said Blair.

Shift work unavoidable

Even with evidence of the negative effects of shift work, the reality is some shift work will always be necessary, especially for health-care workers.

“Health care is a 24-7 operation,” said Catherine Kidd, executive director of disability management and safety at Vancouver Coastal Health.

To help ensure the health of its shift workers — about 80 per cent of direct care providers work shift work — Vancouver Coastal Health developed a Shifting to Wellness for Health Care Workers program three years ago.
The program, available online, focuses on nutrition, exercise and how to manage fatigue, stress and sleep disturbances, said Kidd.

“It’s quite a holistic approach to all the things that individuals need to consider to be well. But when you’re a shift worker, you have to have other thoughts around what kinds of food should you eat when you’re working nights, when should you have your big meal, all those sorts of things,” she said.

The program advises workers to eat their main meal as early in their day as possible to ease digestion, which will improve their energy. Workers should eat lighter, healthy foods throughout their shift to avoid fatigue. They should also taper off their liquid consumption throughout their shift to ensure more uninterrupted sleep, said Kidd.

The hospital also encourages shift workers to exercise, just not before going to bed, she said.
“We really encourage shift workers to consider how they can make exercise part of their interactions with their family and friends,” she said.

Denmark compensates shift workers who develop breast cancer

In 2009, Denmark became the first country to compensate women who work night shifts for occupationally related breast cancer. To qualify for payments, a woman must have developed breast cancer after having worked at least one night shift a week for 20 to 30 years. Most of the women receiving benefits worked as nurses and airline attendants.

In Canada, however, none of the provincial workers’ compensation boards recognize cancer as a shift-work-related occupational illness.

“We view shift work as a potential health and safety issue,” said Paul Moist, national president of the Canadian Union of Public Employees (CUPE).

When it is necessary, CUPE tries to negotiate provisions into collective agreements to mitigate the effects of shift work, such as providing more vacation time for shift workers, educating workers on healthy living practices, reducing rotating shifts and proper break periods, he said.

While some shift work is inevitable, such as with firefighters, police and nurses, for other organizations it is not necessary, he said.

“We find economic issues sort of drive more shift work,” said Moist. “We’re trying to keep that to a minimum.”

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