SHIFT WORK AND HEALTH

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OVERVIEW OF CIRCADIAN RHYTHMS

Numerous psychological and physiologic variables have been found to have a demonstrable 24-hour, circadian (Latin: circa = about, and dies = a day)60 rhythm, including body temperature, the sleep–wake cycle, cardiovascular parameters, cognitive performance, endocrine and immunologic factors, therapeutic response to certain medications, and psychological variables of mood and anxiety (Fig. 1).64, 125

If these biological rhythms merely reflected responses to external time cues, they would be of

CIRCADIAN RHYTHMS AND SHIFT WORK

The major function of the circadian system is the internal sequencing of physiologic events and metabolism. Biological processes are thereby coordinated for optional functioning of the organism. Restorative functions of sleep are maximized by the normal phase relationship of biological rhythms during the nighttime hours.

For the nightshift worker, however, the activity at night will be out of phase with the circadian body temperature and other coupled rhythms. In addition, because individual

Night Work and Sleep Deprivation

The most obvious deviation from normal life for night workers is having to stay awake during the night and having to sleep during the day. Night workers typically get less sleep than their day-working counterparts, and regular night work is associated with chronic sleep deprivation.142, 144 The sleep length of night workers is 15% to 20% that of day and afternoon workers, averaging 4 to 6 hours, compared with 7 to 9 hours respectively.5, 145 In addition to being shorter than night sleep, day

Gastrointestinal Disorders

Gastrointestinal dysfunction is common in shift workers.13, 34, 95 Gastritis or other digestive disorders have been an explanation frequently given by shift workers for absenteeism and for switching to day work for health reasons.156 Symptoms of GI disturbance arising during shift work may not completely resolve after returning to a normal schedule.1, 154

Some studies have not found an increased incidence of peptic ulcer disease (PUD) in shift workers, but the majority of studies addressing this

AGGRAVATION OR EXACERBATION OF MEDICAL DISORDERS

The effectiveness of many medications varies with the time of day the medication is taken because of circadian rhythms in metabolic parameters as well as target organ responsiveness. Irregular work schedules may interfere with the application of chronopharmacologic principles. In addition, workers with irregular schedules lack consistent routines, making it difficult to remember to take medications. Shift work also may aggravate certain medical disorders related to circadian rhythm disruption,

Psychosocial Disruption

Shift work increases social and family stress.33, 57 Night work, evening work, and irregular schedules often make it difficult for shift workers to fulfill parenting and social responsibilities.108, 133 Working the second shift (late afternoon and evening) is usually the most disruptive for family interaction. Shift work schedules may create a significant strain on the marriage relationship,130, 165 and higher divorce rates have been reported for shift workers31, 127 and for shift work dropouts

Preplacement Assessment

Recommendations for medical evaluations of workers before they begin night work assignments have been made by occupational medicine practitioners and researchers involved in studying the health effects of shift work.37, 82, 105, 125 Identification of individual characteristics associated with poor tolerance of night work is recommended, not with the goal of disqualifying workers for night work, but with the recognition that, for some, night work may medically not be advisable. In most

Sleep Strategies

The specific shift work schedule design is a significant variable affecting the degree of sleep difficulties experienced by individual shiftworkers. A discussion of schedule design considerations is beyond the scope of this article, however Knauth74 recently provided detailed practical recommendations for achieving chronobiologically sound shift schedules.

Within the constraints of the shift schedule, individual workers can apply chronobiologic principles to determine the best time for sleeping.

SUMMARY

Night work and rotating shift work disrupt the circadian timing system. This disruption may produce significant deleterious symptoms in some workers. Certain medical conditions may be aggravated by shift work scheduling, and shift workers are at increased risk of experiencing cardiovascular, gastrointestinal, and reproductive dysfunction. Vulnerable individuals may develop clinical depression when working shifts.

Primary care practitioners may intervene by providing medical surveillance and

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    Address reprint requests to Allene J. Scott, MD, MPH, Armstrong Occupational Health Care, One Nolte Drive, Building 600, Suite 650, Kittaning, PA 16059

    *

    Department of Environmental and Occupational Health, University of Pittsburgh Graduate School of Public Health, Pittsburgh; and Armstrong Occupational Health Care, Kittaning, Pennsylvania

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