Shift Work Hazards

Allene Scott, M.D., Kittaning, PA

Overview Of Circadian Rhythms

Numerous psychological and physiological variables have been found to have a demonstrable 24-hour, circadian (Latin: circa = about, and dies = a day)60rhythm, e.g., body temperature, the sleep-wake cycle, cardiovascular parameters, cognitive performance, endocrine and immunological factors, therapeutic response to certain medications, and psychological variables of mood and anxiety. 64,124,125

If these biological rhythms merely reflected responses to external time cues, they would be of little consequence for the shiftworker. However, circadian rhythms have an endogenous component. The existence of a biological clock in humans has been repeatedly demonstrated in temporal isolation studies, in which subjects are separated from all environmental and social time cues.162 Under normal nychthermal conditions (daytime activity and night time sleep), the circadian system is synchronized with the 24-hour solar day by external triggers to which the biological clock is responsive. The normal phase relationships of the multitude of biological rhythms is effected by an orchestrated response to the internal pacemaker.

The time cues, which are capable of entraining the biological clock to an external periodicity, have been termed "zeitgebers" (German: time giver). Zeitgebers allow the biological clock, which runs a bit slower than the 24-hour day, to be reset and entrained to the 24-hour day.16 Various agents have been shown to act as zeitgebers including light, social factors, and behavioral patterns such as eating schedules, and sleep/wake schedules.155,157 Social cues, the sleep/wake schedule, and the rest/activity cycle are relatively weak zeitgebers in comparison to sun light (or electrical lighting of at least 7,000 -13,000 lux).44 The phase-shifting effect of light on the circadian timing system is secondary to its suppressing action on the secretion of melatonin by the pineal gland. Melatonin, induces sleep and depresses the core body temperature.14

Circadian Rhythms And Shiftwork

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

For the night shift worker, however, the activity at night will be out of phase with the circadian body temperature and other coupled rhythms. In addition, because individual biological rhythms re-entrain to a time shift at different rates, each time the work schedule rotates, for a period of time after the time-shift, the circadian system will be in a desynchronized state. For example sodium and potassium excretion are closely linked in a stable rhythmic environment, but have significant differences in their re-entrainment to phase shifts.88 The sleep/wake rhythm adjusts faster than the body temperature rhythm 161 and activity re-entrains faster than physiological functions.160

Circadian rhythms are more easily re-entrained, after a time shift, if all the important zeitgebers, including the light/dark cycle, are synchronously shifted, such as occurs with transmeridian flights. For shiftworkers, zeitgebers shift in a nonsynchronized manner.17 Knauth and Rutenfranz 73 failed to find complete inversion of the body temperature rhythm in shiftworkers even after 21 consecutively worked night shifts, and concluded that the circadian system never fully adapts to night work. Other field studies of shiftworkers have also found adaptation to night work to be incomplete.99,115

Shiftwork And Health

Night Work and Sleep Deprivation

The most obvious deviation from normal life for night workers is having to stay awake during the night time and having to sleep during the daytime. 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 15-20% that of day and afternoon workers averaging 4-6 hours compared to 7-9 hours respectively.7,145 In addition to being shorter than night time sleep, day sleep is of a poor quality due to disruptions by frequent awakenings and deviations from the normal REM/non-REM sleep stage pattern. 7,12,129,148,159

The etiology of the sleep problem of night workers is multi-factorial. Several studies have demonstrated that a major determinant of sleep duration and quality is the endogenous circadian system. 8,9,39 However, social and job schedule requirements, domestic responsibilities, and environmental conditions also may significantly contribute to the sleep problems of night workers. 55,72,122,143

The chronic partial, sleep deprivation of night workers can have significant negative effects on job performance and social functioning. Sleep deprivation is associated with increased irritability and generalized fatigue which can compromise social and domestic interaction.54,59,70 In situations where falling asleep or decreased alertness threatens individual or public safety, shiftwork related sleep deprivation is a public health concern.

Jet Lag versus Shift Lag

Although physician training in chronobiology is often limited, familiarization with chronopharmacological applications, dealing with the optimum timing of medication administration, has brought with it increasing awareness of the human circadian system. The signs and symptoms of jet lag are also familiar to the medical care provider. However, it may not have been understood that jet lag is an example of desynchronosis due to desynchronization of the normal phase relationships between biological rhythms within the circadian system, and to the external desynchronization between the circadian system and the 24-hr solar day/night cycle to which the biological clock is normally synchronized (entrained). Symptoms of jet lag include (in order of frequency as typically reported by frequent jet travelers): daytime sleepiness and fatigue, difficultly sleeping at night, poor concentration, slow physical reflexes, irritability, digestive system complaints, and feelings of depression. Not surprisingly, studies of the general well-being of shiftworkers, have demonstrated that shiftworkers experience very similar symptoms. 163,164 That is symptoms of "shift lag"79 are essentially the same as those of jet lag (Table 1). However, the symptoms of shiftwork-related desynchronosis have more significance because: 1) the complaints of shiftworkers may not be as readily attributed to the work schedule ; 2) jet-lag symptoms are limited to a few days following travel, while symptoms of shiftwork desynchronosis are often chronic; and 3) the conflict between the shiftworkers work schedule and the predominantly day oriented social/business schedule, is in opposition to reentrainment to night work.

Shiftwork Intolerance

Fortunately for most shiftworkers, symptoms are not debilitating. However, for some, shiftwork-related symptoms are not minor. Surveys of former shiftworkers indicate that health complaints may increase with continued shiftwork and be severe enough to cause the worker to give up a job, often following medical advice. 52,129,154

Up to 20% of shiftworkers, may have a disproportionate amount of symptoms of illness when assigned to chronobiologically, poorly designed shiftwork schedules involving night work.105,118,124 Clinical intolerance to shiftwork has been defined by the presence and intensity of the following set of medical complaints: 1) sleep alterations (subjective self-ratings of poor sleep quality, difficulty falling asleep or staying asleep, etc.); 2) persistent fatigue (not disappearing after time off to rest); 3) changes in behavior (e.g., unusual irritability, poor performance); 4) digestive system problems ; and 5) the regular use of sleeping pills (considered almost pathognomonic of shiftwork intolerance).118,120 Askenazi et al.,18 consider the presence of the symptoms in categories (1),(2),and (5) to be essential to classify a worker as shiftwork intolerant.

Individual factors which predispose to shiftwork intolerance are not fully understood. In general, age over 40-50 years, extreme morningness, and rigid sleep requirements are characteristics which have been associated with decreased tolerance for night work. 5,6,38,58,61,119 A recent review of research assessing circadian factors and shiftwork tolerance18 suggests that: 1) individuals with small amplitudes of certain circadian rhythms, e.g., body temperature, may be more prone to desynchronization of rhythms when subjected to time shifts; 2) some individuals are more likely to experience desynchronization of biological circadian rhythms unrelated to zeitgeber manipulation; 3) and certain individuals are particularly sensitive to rhythm desynchronization with manifestation of clinically significant symptomatology.

As reviewed by Costa,38 factors affecting shiftwork tolerance, in addition to individual susceptibility, include: 1) social, family and community factors; 2) working conditions; and 3)shiftwork schedule arrangements. Shiftwork tolerance must be assessed in the complex framework of interrelationships of biological and social stressors, and work demands with individual differences in shiftworker vulnerability to these stressors.

The term shiftwork maladaption syndrome (SMS) has been used to describe the typical constellation of signs and symptoms seen in shiftwork intolerant workers. In SMS the symptoms are pronounced and instead worsen with continued exposure to shiftwork.105,124 The longer the worker stays on shiftwork, the worse the symptoms become, and eventually, the worker may be fired, quit his job, or be involved in an accident. A worker with SMS is likely to get into a vicious cycle due to the lack of recognition and understanding of the problem by himself/herself and/or by others not familiar with the condition. Inability to adjust family/social life to the work schedule and poor schedule design may significantly contribute to the degree of intolerance.32

Before diagnosing SMS, a detailed occupational and social history should be taken, and the temporal relationship of the symptoms to night work should be assessed. If appropriate shiftwork coping strategies have been instituted, and significant signs/symptoms of SMS persist, the recommended treatment medical restriction from night work. The use of these medications to treat SMS, in place of medical removal, is strongly discouraged.

Shiftwork And Specific Medical Disorders

Gastrointestinal (GI)Disorders

GI dysfunction is common in shiftworkers.13,34,95,106 Gastritis or other digestive disorder has been an explanation frequently given by shiftworkers for absenteeism and for switching to day work for health reasons.156 Symptoms of GI disturbance arising during shiftwork may not completely resolve after returning to a normal schedule.1,154 While some studies have not found an increased

incidence of peptic ulcer disease (PUD) in shiftworkers, the majority of studies, addressing this outcome have. Including non-English reports (reviewed by Costa36), 16 studies, out of 24, evaluating PUD and shiftwork, found shiftworkers to be at greater risk of developing PUD than day workers.

The etiology of gastrointestinal disorders in shiftworkers is probably multifactorial, involving dietary and lifestyle factors as well as circadian disruption. In addition to eating at unusual times, shiftworkers may alter their diet due to lack of eating facilities available during the night shift.117,129,134,141 Circadian rhythm disruption also contributes shiftwork relate GI dysfunction. The night workers' meal times are in conflict with the circadian rhythms in gastric acidity emptying.56,101 Recently the multifactorial nature of peptic ulcer disease has been reviewed. Relevant factors applicable to shiftworkers include: sleep loss and disruption, psychosocial stress, skipping meals, and delayed gastric emptying.85

Cardiovascular Morbidity

Shiftwork schedules have been reported to have deleterious effects on biomarkers of cardiovascular disease. Several studies suggest that shiftwork may increase serum triglyceride and low density lipoproteins.42,75,77 Although there are studies, which have not found changes in lipid profiles related to shiftwork, a recent thorough review of this research concluded that the better studies do indicate that shiftworkers have somewhat higher levels of cholesterol as well as triglycerides.27

Shiftwork has also been associated with hypertension. Lavie and colleagues86 found that shiftworkers, categorized as non-adapters, had a higher incidence of hypertension than day workers. A recent longitudinal study of blood pressure and rotating shiftwork,107 found the cumulative incidence of hypertension was around 3 times higher for younger rotating shiftworkers (18-29 years) than for day workers in the same age group.

Although early studies, concluded shiftwork was not associated with an increase in CVD,1,138 most of the more recent, better epidemiologically designed studies have found an increased risk of CVD associated with shiftwork. Of the three, which have involved permanent night workers,78,134,150 two reported an increased risk associated with working fixed nights. One, a nested case-control study,134 did not find permanent night workers to be at increased risk for workplace death from ischemic heart disease, however, as pointed out by the authors, the study findings were limited due to the small number of night workers (6% were working night shift at the time of the ischemic event).

Most of the studies of CVD and shiftwork have involved rotating schedules. Angersbach et al.13 found no significant excess of CVD in shiftworkers who stayed on that schedule for 10 years, but did find a more than doubled incidence in shiftworkers who had changed to day work. Koller et al.82 found shiftwork drop-outs had a higher prevalence of cardiovascular complaints, and in a subsequent study, Koller80 found cardiovascular disease more common for both shiftworkers and drop-outs. A Swedish retrospective study, of 334 cases and 882 controls, found men with a history of MI significantly more likely to be shiftworkers than controls matched for sex and age.10

A well designed, historical prospective study of paper mill workers76 also found an increased risk of ischemic heart disease (IHD), in rotating shiftworkers. The relative risk (RR)of IHD was found to increase monotonically with increasing years of exposure to shiftwork (6-10 years, RR = 2.0; 11-15 years, RR = 2.2; 16-20 years, RR = 2.8). The association was independent of age and smoking habits. Results from a subsequent prospective study of several thousand nurses, also demonstrated a dose-response effect.71 Another large prospective cohort study 10 reported an increased Standardized Morbidity (hospitalization) Ratio (SMR) (115 for males; 152 for females) for MI among shiftworking subjects.

Results from the Helsinki Heart Study also provide evidence for shiftwork being a risk factor for coronary heart disease (CHD).140 When all shiftworkers were compared to all day workers, the age adjusted RR of CHD was 1.5; and 1.4 when adjusted for age and life-style factors, blood pressure and serum lipids. Exclusion of data from those taking cholesterol lowering medication during follow-up, flattened the risk pattern, suggesting the beneficial effects of the medication was greater for shiftworkers. Compared to white collar day workers, the RR of CHD was 1.3 for blue-collar day workers; 1.9 for 2-shift workers; and 1.7 for 3-shift workers. The researchers concluded that shiftwork is an important part of an occupational gradient in CHD risk among industrial workers. Additional analysis of data from the Helsinki Heart Study139 demonstrated an interaction of shiftwork exposure with life-style factors known to increase the risk of CHD. For shiftworkers, the RR of CHD rose gradually with increasing numbers of adverse life-style factors, but for day workers, no clear dose-response pattern was found. The findings were interpreted to indicate that shiftwork may have a triggering effect on other life-style factors which increase the risk of CHD, and that active preventive intervention is especially important for shiftworkers.

Reproductive Health

Preterm Births and Low Birth Weight

Mamelle et al.89, studied the relationship between occupational fatigue factors and risk for premature birth Although shiftwork was not a component of the fatigue index used, shiftwork was associated with a higher prematurity rate (RR=1.6). McDonald and colleagues90 found rotating shiftwork to be associated with low birth weight, O/E=1.38 (p<0.01), but not preterm birth. Later analysis15 of data from this study, allowing for gestational age, suggested that shiftwork may slow fetal growth and increase the risk of preterm delivery. Nurimen109 found a small association between shiftwork and small-for-gestational age infants.

In their study of pregnancy outcome, Axelsson et al.20 compared night and evening work, working irregular hours outside the hours of 0645-1745, and rotating shiftwork to permanent day work. Working irregular hours was associated with an increased risk of low birth weight. In a recent Chinese study,166 higher proportions of preterm birth (odds ration (OR), 2.0) and low birth weight (OR, 2.1) were found for rotating shiftworkers compared to regular day workers. A subsequent study50 did not find a deleterious effect from doing occasional evening or night work.

Data on permanent night work and reproductive outcomes are very limited. Two studies20,123 did not find an association between permanent night work and increased risk for adverse pregnancy outcomes. However, in one of these studies, only 4% of the female employees interviewed were night workers, and some of these worked nights occasionally. In the other study, 91% of the night workers questioned were part-time. Fortier et al.50 did find a modestly increased OR of 1.45 for delivering preterm, for women working regular evening or night shifts after the 23rd week of pregnancy.

Spontaneous Abortion

McDonald and coworkers91 found an association between rotating shiftwork and an increased risk of spontaneous abortion. Axelsson et al.19 studied the relation between shiftwork and spontaneous abortion in 3358 Swedish midwives. A statistically significant increased risk was found for night work and 3-shift work (OR=1.63 and 1.49 respectively) for those women who worked during the first trimester. When the analysis was limited to first pregnancies, a significantly increased risk was again found for night work (OR,6.89)and for 2-shift work schedules (OR,2.70). There was an insignificantly increased risk for 3-shift schedules. Infante-Rivard et al.68 compared the work schedules of 331 women who had experienced pregnancy loss to 993 gestationally age-matched controls. For fixed evenings schedules, the adjusted OR was 4.17, and for fixed nights, 2.68.

A significantly increased risk of miscarriage has been reported in laboratory employees working shiftwork (RR=3.2).21 Two other studies65,153 also found an increased risk of spontaneous abortion associated with shiftwork. In one, the increase was only observed for rotating shiftwork. In the other, fixed night work was also found to be a risk factor. Axelsson et al.20 reported a statistically insignificant increased relative risk for miscarriage (R=1.44) associated with irregular working hours including rotating shiftwork. Axelsson and Molin22 found an increased miscarriage rate of borderline significance in shiftworkers (OR=2.07).

Eskenazi et al.,48 in their case-control study of physical exertion and hours of work as risk factors for spontaneous abortion, did not find an increased adjusted OR for evening or night work, or for variable shiftwork compared to regular day work. A second negative study,30 designed to determine if employment or preconditions of employment increase the risk of spontaneous abortion, did not find shiftwork schedules or hours of work, to be associated with a significant increased risk of spontaneous abortion. As pointed out by Nurinem,110 in these two negative studies, rotating shifts were part of broad exposure categories and were not analyzed explicitly.

Shiftwork and Subfecundity

The few studies which have been published studying time to pregnancy, raise the possibility that shiftwork and long hours of work may reduce fecundity, particularly of the female partner. Ahlborg et al.,2 who surveyed over 3000 Swedish midwives, reported decreased fertility for rotating shiftworkers or permanent night workers compared to day workers. Bisanti et al.26 found rotating shiftwork by the mother was associated with an increased risk of subfecundity (OR=2.0). A Japanese study on working conditions, found pregnancy rates lower for women doing shiftwork (10.0%) compared to day workers (18.1 %), p<.01.153 Three other studies did not find an association between subfecundity and shiftwork. 111,132,151

Aggravation Or Exacerbation Of Medical Disorders

The effectiveness of many medications varies with the time of day the medication is taken due to circadian rhythms in metabolic parameters as well as target organ responsiveness, however, irregular work schedules may interfere with the application of chronopharmacolgical principles. In addition, workers with irregular schedules lack consistent routines, making it difficult to remember to take medications. Shiftwork also may aggravate certain medical disorders related to circadian rhythm disruption, psychosocial stress and/or sleep deprivation. Table 2 lists conditions that may be exacerbated or aggravated by irregular schedules and/or night work and are thus potential contraindications for shiftwork. Similar recommendations have been made by Costa37 and Koller.81 A brief discussion of some common conditions which may be exacerbated or aggravated by shiftwork follows:

Diabetes Mellitus

Basal insulin secretion and glucose tolerance normally follow a circadian rhythm.114 Plasmainsulin response to intravenous tolbutamide has been shown to peak early in the morning around 0400.126 Insulin response to a glycemic stimulus follows a circadian rhythm, and blood glucose control, when the nutrient level is high, varies with the time of day. In addition, plasma glucose levels in diabetics are higher in the morning than at night.49,93

Mirouse et al.96 has reported a diurnal variation in the effect of the type of meal (simple versus carbohydrates) on blood glucose control in insulin-dependent diabetics. A circadian rhythm has been observed for the gastric emptying response, which limits the rate of digestion and absorption of nutrients. Diets which slow the gastrointestinal digestion of carbohydrates have been reported to be successful in controlling glucose levels in diabetic patients.56,69 Consistent with these observations are research findings on rats which suggests that the timing of meals, relative to the gastric emptying response, may induce changes in the number and affinity of insulin receptors and thus affect responsiveness to insulin.149

Based on the above considerations, regular timing of meals and the use of antiglycemic medications is an important part of diabetic management. Detailed attention to the type and amount of food eaten are also important elements in the clinical management of diabetes. Shiftwork may interfere with the timing and type of meals eaten by workers, which may make compliance with dietary recommendations more difficult for diabetics. In addition, associated circadian rhythm disruption may make it difficult to establish an optimal dosing schedule for pharmacological control of blood glucose levels.

Epilepsy

Sleep deprivation techniques are used to provoke typical epileptic electroencephalographic discharges in patients under diagnostic evaluation for epilepsy.46 Sleep deprivation of 2426 hours can cause electroencephalogram (EEG) activation in epileptics, and in many patients in whom this has been observed, seizures episodes have been related to loss of sleep.113,25,146 Sleep deprivation may activate EEG epileptic activity and sometimes clinical seizures in persons with generalized or focal epilepsy, and may increase the frequency of seizures in some epileptics.20,146 The onset of seizures has also been related to changes in corticosteroid levels which become desynchronized with phase inversions of the sleep-wake cycle.47

Night work is well documented to be associated with sleep deprivation and circadian rhythm disruption. The research findings presented above indicate that seizure events in epileptic individuals may be increased by circadian rhythm disruption and partial sleep deprivation.

Asthma

Circadian rhythms of airway resistance have been demonstrated by pulmonary function testing in normal and asthmatic subjects.116 Over 60% of asthmatic patients awaken from sleep some nights with nocturnal symptoms of airway restriction.152 The nocturnal propensity for respiratory symptoms is strongly related to physiological circadian rhythms of circulating cortisol or epinephrine, decreased dynamic lung compliance and airway patency, and increased bronchial reactivity to allergen triggers.23,97 Chronobiological considerations have been used to optimize effectiveness and minimize adverse side effects of bronchodilators and steroids in controlling asthma.24,112 For regular night workers, it may be possible to adjust the recommended dosing schedule to fit the reversal in the activity/sleep cycle. It is not known if chronotherapeutic considerations can be successfully applied to shiftworkers with irregular sleep/wake schedules and rhythm desynchronization.131 Consistent control of symptoms for rotating shiftworkers may be compromised. On the other hand, it has been suggested that for unmanageable asthmatics, irregular schedules might actually reduce bronchospastic episodes by decreasing the amplitude of the PEFR rhythm.66

Shiftwork And Mental Health

Psychosocial disruption

Shiftwork increases social and family stress.33,57 Night work, evening work, and irregular schedules often make it difficult for shiftworkers to fulfill parenting and social responsibilities.108,133 Working the second shift (late afternoon/evening) is usually the most disruptive for family interaction. Shiftwork schedules may create a significant strain on the marriage relationship,130,165 and higher divorce rates have been reported for shiftworkers31,127 and for shiftwork dropouts29 than for day-workers. Social and family life factors may interface with biological factors by interfering with good sleep hygiene and other chronobiological coping strategies. This disruption may contribute significantly to the shiftwork intolerance seen in individuals with Shiftwork Maladaptation Syndrome (SMS) which shares much in common with depressive symptomatology.106,120

Shiftwork and Depression

Chronobiological observations have raised concern that shiftworkers may be at increased risk of developing affective mood disorders. Jet lag and shift lag include symptoms of psychophysiological disturbances of well-being, resembling symptoms of affective disorders, such as irritability, fatigue and poor sleep, apathy, poor appetite, and psychosomatic complaints.3,67,92,120 In addition, changes in mood have been shown to be associated with irregularity of sleep patterns, and with sleep deprivation.28,54,137

The potential for shiftwork to increase risk for depression is suggested by studies of patients diagnosed with a depressive disorder which demonstrate that these patients typically have a dysfunction of the circadian system.63,64,158 Several studies indicate that imposed time shifts may lead to the development of clinical depression in vulnerable individuals. An increase in depressive symptoms has been reported after experiencing a phase-delay time shift.41 In bipolar patients, episodes of mania have been triggered by time zone changes and by a night of sleep deprivation. Manic symptoms have been successfully managed by regularization the patient's schedule.51 Several studies of shiftwork suggest shiftwork may predispose certain individuals to affective disorders. Tasto et al.136 reported nurses to have increased scores on depression profiles during their first months of working rotating night shifts. In a study of retired workers, cases of depression were more frequent in shiftworkers compared to day workers.94 Finally, results of a pilot study125 of major depressive disorder (MDD) in current and former shiftworkers, found a monotonic trend of increasing prevalence of MDD with increasing years of shiftwork exposure.

Medical Screening And Surveillance

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 shiftwork.37,82,105,125 Identification of individual characteristics which are 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 situations, a pre-placement examination will provide an opportunity to make workers with medical conditions which may be aggravated by shiftwork aware of their situation, and if night work is to be tried, to plan appropriate medical supervision and coping strategies. Consultation with a specialist may be necessary before making a disqualify fitness-for-duty determination from night work.

Medical Surveillance

On going medical surveillance including periodic medical examinations, and appropriate laboratory testing has been recommended for rotating and permanent night workers. In addition follow-up evaluations of day workers who have left shift work for medical reasons has been advised.37,82 The frequency of medical surveillance examinations is somewhat arbitrary. However, recommendations are consistent in advising evaluation during the first few months after beginning shiftwork and then at regular, but less frequent intervals, depending on the work schedule and the age of the worker. A reasonable schedule has been outlined by Harma.61

Components of medical surveillance evaluations should include a review of symptoms including those associated with shiftwork intolerance. Questions should also be directed toward identifying poor nutritional habits, and changes involving the usage of alcohol, tobacco, caffeine, and sleeping pills. Assessment should be made for signs and symptoms suggesting aggravation of underlying medical conditions.

Diagnostic testing should include serum lipoprotein and triglyceride levels, blood pressure measurements, and weight and body fat assessment. The medical surveillance program for shiftworkers should include educational/counseling opportunities related to the assessment and optimization of shiftwork coping strategies.37,61

Countermeasures

Sleep Strategies

The specific shiftwork 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 chapter, however Knauth72 has recently provided detailed practical recommendations for achieving chronobiologically sound shift schedule systems.

Within the constraints of the shift schedule, individual workers can apply chronobiological principles to determine the best time for sleeping. After working the night shift, going to bed as soon as possible after arriving home will usually maximize sleep length. Workers often benefit from taking a nap for about 2 hours, in the evening before beginning a run of night shifts. Other recommendations for rotating work schedules have been addressed by Monk and Folkard.100 Applying "Sleep Hygiene," techniques (regular procedures and behavioral rules which enhance the ability to fall asleep and stay asleep) initially developed to help patients with primary insomnia, is also recommended for shiftworkers. Recommendations for a good sleep hygiene program have recently been summarized.43

Environmental considerations to decrease sleep disruptions, include: 1)sound proofing the bedroom from day time noise; 2)eliminating sunlight with appropriate room darking shades, curtains, or shutters; and 3)having air conditioning available for warm daytime temperatures are which not conducive for sleeping. Eye shades and/or ear plugs may be useful. The phone should not ring into the bedroom during the scheduled sleep time. The shiftworker's daytime sleep should be as protected from interruption as the normal night time sleep hours are for the rest of society!

Diet and Exercise

Caffeine should not be ingested closer than around 5 hours before bedtime.4 Shiftworkers are advised to limit the dose to around 300 milligrams of caffeine per day,and to avoid caffeine during the last half of the evening shift or night shift, since the worker's bedtime will come soon after getting home. Fruit juice is good alternative drink for the second half of the shift.

Good dietary habits and exercise are recommended for all workers for preventive health reasons. These recommendations, of course, apply to shiftworkers as well as regular day workers. Based on the research discussed above, concerning CVD and shiftwork, it is even more important for shiftworkers to follow preventive health recommendations for reducing the risk of coronary heart disease. Additional dietary precautions for shiftworkers include avoiding heavy, greasy or otherwise difficult to digest meals before bed time or during the night shift.35,85 There is no consistent evidence to date that dietary manipulations, such as the "jet lag diet,"45 can speed up adjustment to time shifts.

Physical fitness training has been demonstrated in shiftworkers to reduce general fatigue and sleepiness at work, increase sleep duration somewhat, and decrease musculoskeletal symptoms. Recommendations for exercise for shiftworkers include: 1) Moderate physical exercise is preferred over intensive training; 2) Exercise should be done a few hours before the main sleep period; and 3) For morning or day shifts, the best exercise time is after the shift. After night shifts, the exercise should be done before an evening nap.61,62

Family Support/Education

In order for individual coping strategies to be effective, families must be involved. In addition, the shiftworker must remember the toll that the shiftwork schedules may take on the rest of the family. The provision of educational materials for both the worker and family is essential for successful coping with shiftwork schedules. Several publications, which review strategies for increasing worker and family tolerance of shiftwork schedules are available, to assist employees and their families in coping with shiftwork.83,98,100,121

Summary

Night work and rotating shiftwork disrupt the circadian timing system. This disruption may produces significant deleterious symptoms in some workers. Certain medical conditions may be aggravated by shiftwork scheduling, and shiftworkers 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 educational programs for their shiftworking patients and their families.

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