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 the following 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 the key findings from the review of shift work, sleep duration and their respective effects on health.
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 non-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 the previously discussed 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.
Mechanism of action
Not getting enough sleep 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.
Notable quotes from the research review
“Observational studies suggest that sleep is extended above eight hours for the first day off after a spell of shift work.”
“Evidence supports acute sleep loss but not chronic sleep loss among shift workers. It is still possible that shift schedules with a few days off [versus seven off and seven on], limited rest time between shifts [less than 11 hours], or a low frequency of evening shifts [permanent evening shift workers sleep more than other shifts], may be related to chronic sleep loss.”
“Both subjective and objective sleep measures indicate that night work and early morning work are associated with reduced sleep and that about 20 to 30 percent of shift workers report insufficient sleep and excessive sleepiness in relation to night and early morning work.”
“Moderate but not conclusive support exists for a link between shift work and adverse health outcomes relating to cardiovascular disease, type II diabetes, cancer and occupational accidents.”
“The best supported method for improving sleep in shift workers includes having a forward rotating shift system (day-evening-night) and avoiding short recovery periods (less than 11 hours).”
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; 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.
