1. Introduction
Following the industrial revolution, societies began to organize themselves according to the time that individuals dedicated to work in a dichotomy of “time inside work” versus “time outside work” [ 1 ]. Until the middle of the 20th century, this working time was almost exclusively translated into conventional working hours (i.e., working on weekdays from morning to afternoon/evening, with rest on the weekend) [ 2 ]. However, with the evolution of societies, technology, and the economy, organizations were faced with the need to increase working time, in some cases extending the working time to 24 h a day, 7 days a week, leading to the growth of nonstandard work schedules [ 3 4 ]. Such arrangements include, among others, shift work, night work, evening work, and weekend work.
Shift work tends to be defined as an “organization of daily working hours in which different teams work in succession to cover more or all of the 24 h” [ 5 ] (p. 89). According to the Sixth European Working Conditions Survey of the EU-28 in 2015, 19% of workers performed night work, and 21% worked in shifts [ 6 ]. In the USA, according to the National Health Interview Survey (NHIS 2015), about 26% of workers worked in shifts, whether in the evening, at night, or on rotating shifts [ 7 ]. However, shift work and night work have been identified in the literature as the most harmful schedules for workers [ 3 8 ], and their negative impacts can translate into three primary domains: health, family and social life, and the organizational context.
In terms of health, problems tend to arise due to the circadian disturbance to which the workers are subjected. When shift work involves working at night, it requires an inversion of the workers’ sleep–wake cycle, which can lead to disturbances in their circadian systems [ 9 10 ]. This has been associated with several health problems. Specifically, the literature has identified several health problems associated with shift work and night work, including sleep problems [ 11 ], cardiovascular problems [ 12 13 ], psychological problems [ 14 ], oncological problems [ 15 16 ], and problems with the female reproductive system [ 17 18 ]. For example, in the meta-analysis by Yuan et al. [ 16 ], a positive relationship was found between long-term night work and the risk of breast cancer, digestive cancer, and skin cancer. The authors also found that the risk of breast cancer increased by 3.3% for every five years of night work. In cardiovascular terms, Ahmadi et al. [ 12 ] found differences in the DNA methylation of circadian genes between shift workers and day workers. This circadian disruption may be related to increased cardiometabolic risk and, consequently, cardiovascular disease. Additionally, in an integrative literature review conducted in 2020, it was revealed that shift workers were more likely to have sleep problems, fatigue, depression, and burnout [ 11 ].
In the family and social domain, shift work requires working during periods that are highly valued from a family and social point of view, such as evenings, nights, and/or weekends. Temporal desynchronization with the family and/or society can trigger conflict between the two spheres of an individual’s life (work and family) [ 19 20 ]. This conflict can lead to problems in family relationships and/or consequences for other members of the household. In fact, the literature has found negative relationships between shift work and the work–family interface [ 21 22 ], children’s well-being [ 20 ], and marital satisfaction [ 23 ], among others. For example, in a study by Zhao et al. [ 22 ] involving 452 fathers and 756 mothers, shift work was associated with higher work–family conflict. These irregular work schedules were also positively related to psychological distress either directly or indirectly, in this case through work–family conflict. Furthermore, in the literature review by Li et al. [ 20 ], parents’ nonstandard work schedules were associated with negative child developmental outcomes (e.g., mental health issues, obesity, and behavioral problems). Parental depressive symptoms, low-quality parenting, and a less favorable home environment were some of the factors that could provoke this negative association.
In the organizational context, the literature has found an association between shift work, especially night work, and variables such as safety, productivity, or worker absenteeism. These associations began to gain greater attention when it was realized that accidents with major impacts, such as the 1986 Chernobyl nuclear accident in Ukraine, occur mostly during night shifts [ 5 24 ]. In terms of safety, some studies [ 25 26 ] have pointed to a greater risk of occupational accidents occurring when there is shift work, at night, or during long work shifts (e.g., 12 h shifts). Moreover, the performance of employees may be substandard when they work in shifts [ 24 27 ]. In the literature review by Dall’Ora et al. [ 27 ], working in rotating shifts was associated with degraded job performance, while working at night on a fixed (non-rotating) basis seemed to allow workers resynchronization. However, the demands that these work schedules cause in terms of physical and emotional exhaustion can contribute to increased sick leave [ 28 29 ], although not necessarily in a direct way. For example, in the study by Jacobsen and Fjeldbraaten [ 29 ], carried out in a Norwegian hospital, it was observed that there was no direct effect of shift work on absenteeism, but this effect was mediated by work–family conflict and perceived health.
30,31, The various domains associated with shift and night work can interact with each other [ 29 32 ], so this issue gains greater relevance when such interdependence occurs. For example, in a study by Fonseca et al. [ 31 ], carried out in Portugal, burnout was positively related to sleep problems and problems with family life. Likewise, in the literature review of Bastos and Afonso [ 30 ], shift work was associated with several health problems, such as sleep problems, mental health problems, and cognitive impairment, which can consequently increase the number of medical errors.
Considering that the issue of shift work can give rise to a multiplicity of negative impacts, not only on the workers themselves, but also in the family and organizational context, the main purpose of this review was to identify the variables studied by the scientific community to understand the various impacts of shift work and night work schedules and their relative interest in terms of frequency. Based on the established purpose, the following research questions were defined:
Q1: What kind of variables (and respective domains) are studied to understand the impacts of shift work and night work?
Q2: What is the relative interest in the variables identified by the scientific community in terms of the frequency of these variables in the analyzed studies?
Although literature reviews on the impact of shift and night work are relatively common, particularly in a specific domain (e.g., sleep, cardiovascular, or oncological problems), simultaneous analysis of the various impacts and respective frequencies is scarce.