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Safety & Health Effects of Shift Work - ASSE Members

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hythms, a 24-hour rhythm that makes most people want<br />

to sleep between midnight and 6:00 a.m. (Scott, 2010)<br />

and be most active between noon and 6:00 p.m. (Bird &<br />

Mirtorabi, 2006). When an individual works night shifts<br />

or rotating shifts, these rhythms become out <strong>of</strong> sync with<br />

what the person is doing, resulting in a loss <strong>of</strong> synchronicity<br />

between the body’s schedule and the worker’s<br />

schedule. This results in impaired sleep and because “the<br />

circadian clock controls the body temperature, hormones,<br />

heart rate and other bodily functions” (Scott,<br />

2010), shift workers are more prone to a variety <strong>of</strong> illnesses.<br />

Bird and Mirtorabi (2006) list these health issues<br />

associated with shift work: sleep disruption and sleep<br />

deprivation, cardiovascular disorders (including high<br />

cholesterol and triglycerides); gastrointestinal disorders,<br />

diabetes, epilepsy and asthma.<br />

Some studies even indicate that night workers may be<br />

more impacted by exposure to toxic substances and chronic<br />

infections (Dembe, 2009). Cancer has also been implicated<br />

as a possible effect <strong>of</strong> shift work. According to Roan<br />

(2008), “the evidence for an increased cancer risk is so<br />

compelling that the International Agency for Research on<br />

Cancer, a unit <strong>of</strong> the World <strong>Health</strong> Organization, declared<br />

that shift work is ‘probably carcinogenic to humans.’”<br />

ADDITIONAL CONSIDERATIONS FOR<br />

OLDER WORKERS & FEMALE WORKERS<br />

The subjects <strong>of</strong> many studies have been primarily<br />

male, but research has indicated that women working<br />

shift work may also be susceptible to an increased risk <strong>of</strong><br />

breast cancer due to suppression <strong>of</strong> melatonin during<br />

night shifts (Ross, 2009) and to reproductive problems<br />

(Dembe, 2009). According to Bird and Mirtorabi, female<br />

shift workers have an increased incidence <strong>of</strong> irregular<br />

menstrual cycles, spontaneous abortions, premature<br />

delivery and low-birth-weight babies. Ross also notes<br />

that some evidence <strong>of</strong> shift work is linked to preeclampsia<br />

or convulsions resulting from high blood pressure in<br />

pregnancy, which can endanger both mother and baby.<br />

Overall, men have a higher incidence <strong>of</strong> cardiovascular<br />

diseases (including hypertension), but women shift<br />

workers have a higher prevalence <strong>of</strong> gastrointestinal,<br />

genitourinary, endocrine (diabetes and thyroid) and<br />

blood disorders (anemia) disorders.<br />

A second element <strong>of</strong> the population who may be<br />

more affected by working shift work than other workers<br />

in terms <strong>of</strong> health and well-being is the aging workforce.<br />

Costa and Sartori (2007) state, “In many epidemiological<br />

studies, the critical factor for reduced tolerance to shift<br />

work reported to be between 40 and 50 years old.” They<br />

attribute this to a decreased ability for the circadian clock<br />

to adjust to night work and an increase in sleep disturbances<br />

because <strong>of</strong> lowered responsiveness to light. Costa<br />

and Sartori (2007) indicate that health deterioration with<br />

age is more prevalent in shift workers due to chronic<br />

fatigue and sleep disturbances.<br />

Specifically, Costa and Sartori (2007) point to epidemiological<br />

studies to demonstrate that the relative risk<br />

for coronary disease is 1.3 times as high for shift workers<br />

than daytime workers, but the risk is 1.6 times for<br />

men and 3.0 times higher for women shift workers<br />

between the ages <strong>of</strong> 45 and 55.<br />

THE IMPACT OF SHIFT WORK ON ACCIDENT FREQUENCY<br />

Many experts have weighed in on the impact <strong>of</strong> shift<br />

work and consequent sleep deprivation. Schmid (2011)<br />

says that it can make a driver “as impaired as someone<br />

with enough alcohol in his blood to be considered a<br />

drunk driver.” Scott (2010) says that research studies<br />

show that nurses experience significant<br />

decreases in alertness when on<br />

night shift and that the medical error<br />

rate for healthcare works increases<br />

by 6%, 17% and 35% on the first<br />

three successive shifts. In a study <strong>of</strong><br />

nuclear power plant operators<br />

(2008), task performance ability was<br />

shown to depend on the time <strong>of</strong> day<br />

and that shift work “[aggravates] the<br />

nocturnal decline in cognitive abilities<br />

. . . due to a chronic sleep debt<br />

that shift workers carry over to the<br />

night shift and also to day shifts following<br />

early morning shift.”<br />

Further, in 2006, it was reported that about 25% “ . . .<br />

<strong>of</strong> all train accidents are related to fatigue and long working<br />

hours among rail crews” (Dembe, 2009). Accident frequencies<br />

related to shift work have been reported to be due<br />

to disruption <strong>of</strong> circadian rhythms and lack <strong>of</strong> quality<br />

sleep. Ross (2009) supports this stance with his research<br />

that indicates significantly higher rates <strong>of</strong> serious injury for<br />

nights compared to days, particularly when shifts exceed<br />

12 hours and that loss <strong>of</strong> as little as one hour <strong>of</strong> sleep a<br />

night can impair alertness. Parker, et al. (2007) hypothesize<br />

that people on rotating shifts are twice as likely to report<br />

accidents or mistakes and that rotating shift work is shown<br />

to be associated with lapses <strong>of</strong> attention, longer reaction<br />

times and increased error rates. They attribute these trends<br />

to fatigue, stating that “fatigue undermines intellectual and<br />

emotional functioning.”<br />

EMPLOYER ACTIONS TO MITIGATE<br />

THE EFFECTS OF SHIFT WORK<br />

<strong>Shift</strong> work is necessary for public safety, medical<br />

care, power production, manufacturing and other industries.<br />

However, employers can take steps to mitigate the<br />

safety and health effects, including scheduling design,<br />

workload distribution, environmental factors and wellness<br />

programs. Employers can explore the best rotational<br />

schedule, including length <strong>of</strong> shift, forward or backward<br />

rotation and amount <strong>of</strong> time between shifts.<br />

Studies indicate that the length <strong>of</strong> shifts, forward versus<br />

backward rotation and the length <strong>of</strong> time <strong>of</strong>f have a<br />

significant effect on employees’ ability to adapt, prevent<br />

Employers and<br />

employees can take<br />

steps to mitigate<br />

the effect <strong>of</strong> shift<br />

work, the most<br />

important being<br />

careful design <strong>of</strong><br />

shift schedules.<br />

11<br />

Safely Made www.asse.org 2011

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