Shift work linked to heart attack, stroke

Night workers face steepest increase in risk (41 per cent) for coronary event: Study
By Amanda Silliker
|Canadian HR Reporter|Last Updated: 09/10/2012

Shift workers are more likely to experience major vascular problems, such as a heart attack or stroke, than colleagues who work the day shift, according to a Canadian-led study.

Shift work is associated with a 23 per cent increased risk of heart attack, a 24 per cent increased risk of a coronary event and a five per cent increased risk of stroke, found “Shift Work and Vascular Events: Systemic Review and Meta-Analysis,” published July 26 in the online British Medical Journal (BMJ).

“Some doctors are now calling shift work the new carcinogen,” said Don Melnychuk, director of Nadon Consulting in Edmonton and a specialist in stress, fatigue and shift work. “All the writing is on the wall with regards to cardiovascular disease and what shift work does to your different cycles and it was just a matter of time before this happened — and it will get worse before it gets better.”

Night shifts are associated with the steepest increase in risk (41 per cent) for coronary events, found the study, which pooled results from 34 international studies involving more than two million people.

In Canada, one-third of the population works some form of shift work, including evening or night shifts, rotating schedules, split shifts, on-call or casual shifts, 24-hour shifts, irregular schedules and other non-day schedules, according to Statistics Canada.

It is estimated about seven per cent of heart attacks, 7.3 per cent of all coronary events and 1.6 per cent of strokes are directly related to shift work in Canada, found the study.

“It’s a pretty significant impact at the population level just because shift work is such a prevalent employment pattern,” said Dan Hackam, study co-author and an associate professor and clinical pharmacologist at the University of Western Ontario in London, Ont.

One reason why shift workers face an increased risk of heart problems is because shift work disrupts the body’s natural circadian rhythm, he said.

“We’re just not hard-wired to work in the middle of the night,” said Hackam. “In terms of our genetic evolution, we were likely sleeping in a shelter in the dark in the middle of the night with no exposure to electric light, which we know suppresses melatonin secretion and raises blood pressure and heart rate.”

When the circadian rhythm is out of whack, it also affects eating. A worker would normally be fasting at night while he is asleep but if he is a shift worker, he has no choice but to eat at night when the body would normally be fasting and conserving energy during the recovery phase, said Hackam.

“It’s hard to eat decently in the middle of the night,” he said. “Unless you’re very good about bringing food from home and have facilities to prepare it at night, you’re likely to be eating fast food or junk food if you’re a night shift worker.”

This eating pattern can also contribute to weight gain, putting shift workers at an increased risk for vascular problems, said Melnychuk. Because the whole circadian system is so thrown off with shift work, it affects the fat-controlling hormone called leptin, which controls appetite, he said.

“Why a lot of shift workers gain weight is because they’re hungry all the time, and part of the reason for that hunger comes from the lower levels of leptin — sleep deprivation upsets the leptin production and that’s why shift workers eat a lot,” he said.

Typically, shift workers are overweight by 20 to 30 pounds and that’s after 10 to 15 years of shift work, said Melnychuk.

Employers should encourage workers to lose weight and provide opportunities for them to exercise, such as a discount for a gym membership or workout room on-site, he said. All employees should be given a pedometer, heart rate monitor and blood pressure monitor — which altogether costs about $100 — to keep track of their health risks, he said.

Shift work also negatively affects work-life balance, which can put these workers at an increased risk for health issues, said Dhananjai Borwankar, a technical specialist in training and education services at the Canadian Centre for Occupational Health and Safety (CCOHS) in Hamilton.

“Shift work can also impact social behaviours, so it can put psychosocial stress on individuals, which can heighten their stress response, which can make it difficult for individuals to maintain healthy lifestyles,” he said.

“It may be difficult if you’re working an evening shift or a rotational shift and you’re used to being part of sports, it may make it difficult to enjoy those activities.”

Employers should also assess their scheduling practices and make sure they are minimizing the number of night shifts in a row and using forward rotation scheduling — day shift, afternoon shift, then night shift — because it works better with the circadian rhythm, said Borwankar.

They should also ensure employees are taking sufficient breaks throughout their shifts and they have enough staff so employees can get enough rest between shifts, he said.

The schedule should include some weekends and evenings off for each employee and it should be predictable so employees can make personal arrangements, said Borwankar.

Does shift work attract unhealthy workers?

The last possibility of why shift work is linked to an increased risk of heart issues is the potential selection of unhealthy individuals into shift work, said Hackam.

“(Our study) did adjust for lifestyle factors like smoking, socio-economic status, sedentary behaviour and still found increased risk with shift work. But it’s possible shift work represents a marker rather than a cause of cardiovascular events because we might be selecting people that are less well-off to begin with.”

Helping employees control these risks can reduce the number of safety incidents at a workplace, said Borwankar.

“And if you have a good schedule, if you can minimize fatigue in employees, you can improve productivity, have happier employees, and all these things work for the employer and for the employee in terms of their overall health and fitness,” he said.

As the world continues to move towards a 24-7 society, shift work and its associated risks will become even more of a problem in the future, said Hackam.

Employers should put together training programs for all shift workers, especially new employees, that address the impact of shift work on the body and how to deal with some of the problems, said Borwankar.

Employers will need to do their due diligence and make sure they have proper systems in place to support shift workers, said Melnychuk.

“Especially with the liability that may come up when someone does get sick or dies, it just pushes it into a new territory and I don’t know exactly where it will go, but if this is what’s happening with shift work, they’re going to have to take care of workers in a much better fashion than they have before.”

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