Effects of Shift Work on Health: Assessment of Sleep Quality, Motor Control and Cardiovascular Risk.

Shift work can exert numerous effects on the temporal and behavioral organization of the individuals. Working hours of shift workers, which are outside the normal daily social program, lead to a circadian desynchronization due to a temporary misalignment between working time and physiological and behavioral functions, similarly to what is observed in the jet lag syndrome. This may lead to deterioration in the sleep quality, reduction in the working ability during waking hours, with sleepiness and a reduction in the vigilance state.

Over the years, the impact of shift work has involved many areas and its effects have been investigated at the cardiovascular (coronary artery disease, hypertension), metabolic (diabetes and obesity) and immunological level. Several investigations provided evidence of the shift work-induced negative results on health, including carcinogenic effects. Consequently, the scientific community paid to these problems great attention.

In analyzing the health effects of shift work, the chronotype of the workers, or their circadian typology, is very important. In fact, the circadian rhythms represent a dimension of the human personality that should not be underestimated. The human being has a temporal organization, determined by the interaction of endogenous and environmental factors, and organizes most of the biological and behavioral activities according to a twenty-four hour period and in sync with the light-dark cycle. It is not worthy to mention that the biological rhythms in humans present interindividual differences that determine precisely the chronotype, which is the tendency to express preferences toward morning or evening activities. Within the population, it is possible to recognize subjects that can be traced to three circadian types: (i) morning-types subjects (M-Types) that tend to be more active and efficient in the first part of the day, (ii) evening-types subjects (E-Types) who find it difficult to get up in the morning and require more time to reach the optimal level of physical and mental efficiency, and (iii) intermediate subjects (Neither-Types, N-Types) that present intermediate characteristics between the previous two.

Previous studies suggested that the eveningness could determine an easier adaptability to the changes determined by shift work. However, the role of the chronotype on this aspect is yet to be related to the type of shift: on one side, the E-Types tend to have more sleep disorders induced by a diurnal working shift. On the other side, the M-Types tend to adapt worst to a night working shift. In any case, shift work determines a growing sleep debt that can have a not negligible impact on the wellbeing and health of the individual.

The association between shift work and cardiovascular risk is very interesting. Sleep at night, in fact, can have important effects on blood pressure. Some studies have shown that a good sleep quality may have potential effects in the prevention of hypertension. Arterial pressure decreases by an average of 10-20% during nighttime hours, so sleep debt could lead to higher average blood pressure over the course of twenty-four hours. In addition, by modifying the circadian rhythms, the shift may lead to an alteration of the autonomic nervous system regulation with hypertensive consequences.