Why female shift workers may be at risk for heart disease

Here at the annual Canadian Cardiovascular Congress in beautiful Vancouver, we’ve learned some bad news about female shift workers.

As researcher Dr. Joan Tranmer – a former nurse herself with over 15 years of experience working rotating shifts –  told her conference audience:

“Women hospital staff working night shifts may be compromising their own health as they try to improve the health of patients.”  

Her research team (based out of Queen’s University in Kingston, Ontario) looked at female hospital employees (mean age of 46) including nurses and a variety of female staff who had to work a variety of shift rotations (admin, lab, equipment technologists).

She examined each of the women’s potential cardiac risk factors associated with what’s known as metabolic syndrome. The syndrome’s five indicators are:

• abdominal obesity (the so-called “apple-shaped” torso)
• high blood pressure
• elevated blood glucose (sometimes called pre-diabetes)
• elevated triglycerides (a kind of blood fat tracked along with cholesterol)
• low levels of HDL (good) cholesterol

Her results showed that one in five middle-aged women who do shift work have at least three of these known risk indicators for heart disease.*

When I sat down with Dr. Tranmer following her Vancouver presentation to find out why the stats seem so grim for female hospital staff doing shift work, here’s what I learned from her:

“We asked women what turned out to be two important questions:  ‘How long did you do shift work?  And are you currently working shifts?’

“When we took women’s age out of the equation, we found that women who had both a long history of working shifts and were still doing shifts today were most at risk for developing  cardiovascular disease.”

And the number of years you continue to work those night shifts may play a significant role in cardiac risk factors. For example, Dr. Tranmer’s study found that metabolic syndrome was present in:

• 8% of those working shifts for less than six years
• 18% in those working 6-15 years
• 74% in those working for more than 15 years

I asked Dr. Tranmer what elements of working shifts contribute to the development of serious cardiac risk factors among the workers themselves. It’s not clear, she replied, adding:

“It is possible that the disruption of biological rhythms, sleeping, eating and exercise patterns may all be factors.”

Previous research done by the University of Maryland had also concluded that in addition to long work hours, lack of time off was a major factor in nurse fatigue and workplace injuries.

And a Statistics Canada survey on the work-life balance of shift workers found that long work hours were also associated with role overload. When shift workers were compared with regular day workers, they were more likely to:

• cut back on sleep
• spend less time with their spouses
• worry about not spending enough time with family

Dr. Tranmer’s study found that age and current shift work status were significantly associated with increased risk of metabolic syndrome, particularly for women who:

• were over 45 years old
• had reached menopause
• had a shift work history of more than six years
• were currently working either 12-hour shifts or rotational shifts

Another serious concern, she said, was her finding that over 60% of study participants had a waist circumference greater than 80 cm (31.5 inches). This is important information for women because abdominal obesity alone is a good predictor for risk of developing heart disease, stroke, high blood pressure, cholesterol issues and type-2 diabetes. The greater your waist circumference, the higher your risk of developing these conditions.

What about all those male shift workers?  Dr. Tranmer explained that much of our understanding about the associations between shift work and health comes  from studies that have predominantly included men, so she wanted to specifically focus on this link in women.

Shift work concerns like this are not new.  Ramazzini (1633–1714) wrote about bakers, innkeepers and soldiers working night shifts. And the advent of the industrial revolution led to many other people working long hours, until legislation was introduced to curtail the worst abuses of a factory-based economy.

But the modern hospital system trend of rotating its employees through 12 hour shifts  began throughout much of North America during the 1980s due to increasing nursing shortages. A number of studies have suggested a link between these extended nursing shifts and poorer health outcomes for both nurses and their patients, including measurably higher incidents of pneumonia and heart attack among patients.  One such study, for example, published in the journal Nursing Research in January 2011, reported:

“Although many nurses like these shift work schedules because of the compressed nature of the work week, the long schedule – as well as shift work in general – leads to sleep deprivation.

“Alertness and vigilance required for providing good nursing care depend upon having an adequate duration of quality sleep and rest, and long work hours can impact the quality of nursing care and can increase the potential for error.”

Because I had worked in a hospital for many years before my own heart attack symptoms hit, and knew how our nurses had often described the last couple hours of an exhausting 12-hour shift, I chose (instinctively but foolishly) to wait until after shift change before I showed up in the E.R. – because I must have assumed that the staff on a new shift would be “fresh” after 7:30 a.m!

Studies have long suggested that sleep obtained during daylight hours or at irregular times is of poorer quality than that obtained during normal nighttime sleep, and we know that there is a significant link between sleep disorders and heart disease. Chronically restricted sleep patterns and the subsequent sleep debt that accumulates over time may be most pervasive in professions like health care that function 24 hours a day, seven days a week.

* Canadian Journal of Cardiology Volume 27, Issue 5, Supplement, p. S69-S70, September 2011

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