work and health

Shift work and health

By Dr. Stefano Casali

Shift work is defined by its continuity, its alternation and its schedules. It stems from the need to guarantee essential services for the entire 24-hour period. Shift work, with alternating or successive teams, is called continuous when you carry out every day, including Sundays and holidays, and requires the constitution of a minimum of 4 work teams (3 teams working in 8-hour shifts and a team of rest); it is usually referred to as «continuous 4 x 8». Shift work, with alternating or successive teams, is called semi-continuous when it is interrupted for weekends and requires the constitution of a minimum of 3 teams: «3 x 8 semi-continuous». The shift generally lasts 8 hours and the same time is carried out for a duration that defines the rhythm of alternation. In most cases it is 7 days or more rarely 5. A final characteristic concerns the times of the beginning of the shift. For most activities the start times are at 5 or 6 in the morning, at 1 or at 2 pm in the afternoon, at 9 pm or at 10 pm in the evening. More rarely at 4, 12, and 20 (CNR Department of Personnel 7/1999; Olson CM, 1984; Magnavita N., 1992).

In general, the shiftista condition implies for the individual a series of modifications of the usual patterns (taking meals, alternating the phases of activity and rest), causing a mismatch between the synchronism of the endogenous circadian system, the environmental synchronisms (in particular the light-dark rhythm) and social, with consequent disturbances of normal circadian rhythms and psycho-physiological functions, starting with the sleep-wake rhythm.

In relation to the frequency we can distinguish the following rhythms: The circadian or nictemeral rhythms (nict- night, -emera day ) whose frequency is about one cycle every 24 hours (in fact between 20 and 28 hours): alternation between waking and sleeping, central temperature cycle of the central temperature. The rhythms infradiani, whose period is superior to 28 hours: the annual, seasonal, monthly rhythms. The ultradian rhythms whose period is less than 20 hours. Many factors concerning individual characteristics and social conditions can interact with working conditions and influence short and long term adaptation (G. Costa, 1990; G Costa., 1999; Melino C., 1992). In fact, not all shift workers have clinically significant symptoms. There is considerable inter-individual variability regarding the ability to react positively to these stressors. The possibility of adapting effectively to alterations, even very significant, of one's own rhythms can be traced back to two orders of factors: extrinsic factors, linked to the type of shift work (such as the direction and speed of rotation of the shift), and intrinsic factors or subjective such as: age, seniority of service and gender, the circadian type, some personological and psychological characteristics (Acts of the 25th Conference, 1996; Magnavita N., 1992). Another element to underline is the quality of the environment, which plays an equally important role: a supervisory task is easier to carry out in a "rich" environment than in a "poor" one, the important factors are the lighting level, the sound level, their temporal modulations, the alternation of different types of significant stimulations. It is well known that situations in which the amount of information has decreased are painful to bear and lead to drowsiness. Vigilance is not maintained at the same level throughout the waking period, it also obeys a circadian modulation. These falls in vigilance can correspond to decreases in the performance of the subject: errors, omission of signals, occur spontaneously increasing with the duration of the work, with monotony, fatigue, the absence of pauses, deprivation of sleep or overeating. (G. Costa, 1990; Olson CM, 1984). It was therefore proposed to enrich the monotonous tasks, in which the signals are too infrequent, with stimulations unrelated to the task but to which the worker must respond.

Physiological adaptability seems to be particularly important, understood as the capacity of each individual to realign, more or less rapidly, the rhythm of the different biological functions, to changes in the sleep-wake rhythm. Another important individual feature is stretch drowsiness. What characterizes sleepy subjects is the high frequency with which they complain of daytime sleepiness and the ease with which they fall asleep, even when conditions would not allow it. Vigilant subjects, on the other hand, often complain of insomnia, fall asleep with difficulty and easily resist sleep. Among the latter, however, there are also those subjects characterized by both good levels of "wakeability" and "sleepability" which, by virtue of their ability to sleep or stay awake on command, should also present the greatest ability to adapt to work at shifts. The two main sources of difficulty for shift workers are the desynchronization of sleep times and the desynchronization of meal times. These disorders are the cause of most spontaneous dropouts in the first months of work in turn (Magnavita, 1992; G Costa, 1990; G Costa., 1999) and should be kept in mind because they betray a bad adaptation.

Sleep disorders consist essentially in permanent desynchronization between circadian rhythms, activity and rest phases and social habits. The duration and quality of sleep of shift workers vary according to the time of the shift and the environmental conditions. The daytime sleep of night shift workers is shortened by about a third and is also, although to a lesser extent, in morning shift workers, who generally give up going to bed earlier in the evening. The deficit in sleep is called into question not only in the worsening of mental performance and vigilance but also among the causes of the feeling of malaise complained about the morning shift workers. The level of noise to which the sleeper is subjected essentially decreases sleep and the sound environment of rest directly affects the ability of the worker especially if he is subjected to mental or supervisory commitment.