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In a review of over 189 literature references, a recent University of Surrey (UK) study concludes that night and extended shift workers acquire less sleep which interferes with work productivity and promotes select health problems including:
- Increased accidents
- Errors (36% higher incidence of seriously improper medical decisions were made by interns working a traditional shift compared to a intervention that excluded extended shifts)
- Metabolic syndrome (decreased HDL cholesterol, elevated triglycerides)
- Glucose intolerance/diabetes
Further, there is some indication of a relationship between long term night work and heart disease and cancer.
The author felt the underlying reason for these problematic work and health developments was related to circadian rhythm desynchrony – performing an activity such as work tasks when the body is producing hormones that encourage rest/sleep. The literature revealed that most long time or permanent night shift workers do not show an adaptation of their circadian rhythm to their work day with less than 25% demonstrating even partial adaptation. Night workers have a marked reduction of daytime sleep hours, suggestive of sleep deprivation.
Night shift workers were able to alter their circadian cycle in select work environments:
- When there was a lack of social/family commitments
- There was no natural morning light at the end of their night shift
The Bottom Line – How This Applies To Ergonomists
This study highlights the potential problems related to working night or extended shifts – poor productivity and health risks. Although changing work methods can reduce the need to work at night, a night shift is unavoidable in some industries. The author suggests that encouraging an adaptive shift of the worker’s circadian rhythms to coincide with night hours may be favorable.
Using light treatment during the biological night can favorably impact melatonin production – a regulator of the sleep/activity cycle. Exercise, social cures, timing of food ingestion, and food content are also felt to influence the circadian clock to varying degrees. Combining a low dose of melatonin, a dark room, and recumbency in the early evening prior to a night work shift would be useful in increasing a worker’s total sleep hours.
If there is a short time commitment to a night work shift, no interference with the normal body rhythms is encouraged outside of alerting stimulants such as caffeine.
Other Key Points
Circadian rhythms are internally (to the body) generated biological sequences. Body functions such as sleep, metabolism, alertness/performance, and cell proliferation are optimally conducted at select times of approximately a 24 hour period – a day. An internal biological clock, positioned in the suprachiasmatic nuclei of the hypothalamus, is thought to govern the body rhythms via a negative feedback loop.
The hormone melatonin, secreted by the pineal gland, is primarily produced during the night-time body state. The concentration of melatonin (it can be measured in the plasma, saliva, or as a urinary metabolite) provides a good indication of the circadian clock time.
The author indicated that switching from a day to a night shift (with a likely 20-24 hours of no sleep), may lead to a performance loss similar to having an illegally high alcohol blood level.
A PubMed search using the words “shift work”, “circadian”, and “melatonin” led to the generation of 189 articles. Studies were narrowed to those that involved night shift work (job activities were performed between 9 pm and 7 am).
This entire study can be acquired at: http://occmed.oxfordjournals.org/cgi/reprint/60/1/10
Article Title: Shift work: coping with the biological clock
Publication: Occupational Medicine, 60:10-20, 2010
Author: J Arendt
Tim Villnave, MSPH, is an ergonomics consultant in the Division of Risk Management for the State of Utah.