By Catherine R. Counts
A State of the Art Review published in The BMJ represents one of the most comprehensive reviews of peer-reviewed literature on shift work, sleep duration and quality, and the impact each has on chronic health outcomes and occupational accidents.
Specifically, the authors studied 38 meta-analyses and 24 systematic reviews that evaluated sleep or shift work and their impact on these 10 chronic health conditions: coronary heart disease, stroke, cancer, type II diabetes, obesity (weight gain), depression, occupational accidents/injuries, all-cause mortality, coronary heart disease mortality and cancer mortality.
Here are three key findings from the review.
1. Shift work and sleep
The shift that is worked impacts the type of disturbance an individual experiences. Workers who start before 6:00 a.m. typically wake up outside of their natural circadian rhythm, resulting in sleep that isn’t refreshing and more difficult to wake up from.
Workers who sleep during the day take less time to fall asleep, don’t wake up intermittently, but typically don’t sleep for more than four to six hours. Evening shift workers are the least likely to report sleep disturbances and the most likely to hit the eight-hour threshold.
The time between shifts also influences sleep duration. Workers with 11 hours or less of time off see a drastic reduction in the amount of time they sleep.
Rotating schedules can negate some of the negative effects of shift work provided that workers are working four or more shifts in a row before taking time off or switching shifts. Those that only work one to three similar shifts in a row see lower sleep duration between the shifts.
Recovering from a lack of sleep between shifts is poorly understood, but some studies have documented that sleep duration during the first day off is typically greater than eight hours.
Shift work sleep disorder (SWSD) is a common problem among shift workers with an estimated prevalence of anywhere from 10 to 23 percent. Although the quality of the research around SWSD is debatable, new diagnoses of SWSD are more likely to occur in night shift workers.
2. Shift work and chronic disease
The largest review of the connection between shift work and heart health concluded that shift workers have a higher risk of myocardial infarctions and ischemic strokes. This effect was most prevalent in night shift workers, while it was not significant in evening shift workers.
Shift workers are also at a higher risk of becoming overweight or obese and more likely to develop type II diabetes. This risk continues to exist even when controlling for a number of confounders.
In 2007, the International Agency for Research on Cancer, an arm of the World Health Organization, argued that circadian rhythm disruptions likely increased the risk for breast cancer.
Although the data from subsequent studies has been mixed, there is enough research to suggest that there is a potential link between breast cancer and night shift work that is dose-dependent, meaning the longer a person works the night shift, the greater their risk.
Other studies suggest there is also a dose-dependent relationship between shift work and prostate cancer. Night shift workers are also at a higher risk for colorectal cancer.
Regardless of these chronic health conditions, when researchers focus solely on the effect shift work has on mortality, the data is inconclusive.
The relative risk of having a workplace injury is increased for shift workers. And there are even a handful of studies that show an increased risk for automobile collisions following a night shift.
3. Sleep and chronic disease
It’s important to note that shift work impacts sleep in both the length that workers are able to sleep and in the quality of the sleep workers can get (typically via their ability to fall asleep and stay asleep).
Short sleep is defined as any cycle lasting between four and seven hours. Its negative correlations heavily mirror that of shift work. Specifically, short sleep is associated with an increased risk of coronary heart disease, stroke, type II diabetes, obesity and/or weight gain, depression, workplace accidents and mortality.
Poor sleep quality can be defined a number of ways, and is significantly associated with workplace injuries, coronary heart disease, type II diabetes, depression and in some cases mortality.
Not getting enough sleep is due to shift work is hypothesized to have a mediating effect on health outcomes. This means that the data exists between shift work and poor sleep, and between poor sleep and adverse health outcomes, but a concrete direct link between shift work and health outcomes is less clear.
4 top takeaways for emergency responders
Emergency responders aren’t immune to the impact of shift work and sleep deprivation. Here are four top takeaways from The BMJ review that are most applicable to paramedics, firefighters, telecommunicators and police officers.
1. Most shift work has a negative effect on sleep quality and sleep duration, particularly those personnel who work early morning or night shifts.
2. Emergency responders need a chance to recover from shift work, this means getting more than 11 hours off between shifts and getting more than a day or two off between bouts of shift work.
3. There is likely a dose-dependent relationship between shift work and many poor health outcomes, meaning that the longer an emergency responder does shift work the higher their risk is for a poor health outcome.
4. The connections between shift work and sleep, and sleep and health outcomes are relatively established, however it’s hypothesized that there is a direct connection between shift work and negative health outcomes.
About the author
Catherine R. Counts is a health services researcher currently completing her doctorate in the department of Global Health Management and Policy at Tulane University School of Public Health and Tropical Medicine where she also previously earned her Master of Health Administration. Counts has research interests in domestic health care policy, quality and patient safety, organizational culture and prehospital emergency medicine. She is a member of the National Association of EMS Physicians and AcademyHealth. In her free time, she trains Bruno, her USAR canine. Connect with her on Twitter, Facebook, or her website, or reach out via email at ccounts@tulane.edu.