By Hidaya Aliouche, B.Sc.Reviewed by Emily Henderson, B.Sc.
Night shifts are considered to be an impediment to alertness and performance as a result of sleep loss and a change in natural circadian rhythms. Across the world, healthcare workers comprise the largest proportion of shift workers to enable the provision of 24/7 emergency healthcare services.
Night shift patterns of work have both negative implications on the individual, as well as those affected by that provision of service; for example negative implications on patient safety and care in the case of healthcare workers, in addition to significant economic and productivity costs.
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The Implications of Night Shift Work on Circadian Rhythms and Sleep Problems
Night shift work is a widely studied variable as it compromises several aspects of human health including homeostasis and well-being.
Night shift work affects individuals at the biological level. The inversion or perturbation of the sleep-wake cycle is a source of stress for the endogenous regulation of the circadian rhythms of biological functions. These are driven by the body clock and can be found in the suprachiasmatic nucleus (SCN) of the hypothalamus.
The SCN is the principal circadian pacemaker in the human brain, and it generates circadian rhythms during periods of rest and activity, as well as affecting core body temperature, the function of the neuroendocrine and autonomic systems, the performance of memory and psychom*otor complex, as well as other physiological and behavioral processes.
The SCN is controlled by environmental cues which include the light-dark cycle. The optimal physiological condition for diurnal animals is to sleep during the night and awaken during the day. Therefore, those who work night shifts are subsequently forced to alter that psychophysiological state, resulting in changes in the fluctuations of biological functions.
Click here to read about circadian rhythm sleep disorders.
Those functions which are typically active during the day and depressed during the night are inverted. The adjustment to the shift in phase occurs at a rate of ~one hour per day but can vary widely according to the duration of the night shift and schedule.
Most workers involved in rotating shift work have to adjust quickly to the variable shift periods, but night shift workers can adjust so long as they maintain an inverted sleep/wake cycle.
When the circadian rhythm is misaligned, those who operate night shifts suffer from feelings of sleepiness, tiredness, insomnia, digestive issues, poorer mental function, irritability, and reduced efficiency.
The Effect of Night Shifts on Sleep
The effects of shift work occur most obviously on sleep, affecting both quality and quantity. The effects depend on the nature of the night shift, i.e. length, frequency, and rest periods in between them as well as the worker’s personality and behaviors.
Due to sleeping during the day, night shift workers have to sleep during the normal rising phase of the circadian rhythm, and this prolongs the period of feeling wakeful. Environmental conditions such as lighting, and noise can also further disturb sleep and exacerbate the period of wakefulness.
So, on average, night shift workers get two to four hours less sleep who is prematurely interrupted. Moreover, night shift workers experience poorer stage two rapid eye movement sleep, which is perceived as being less restful.
There is an increased likelihood of experiencing a sleep deficit during subsequent night shift work; this is most heightened during the second half of the shift which occurs in the early morning, resulting in a greater risk of errors and accidents, especially while traveling.
The Effect of Night Shift Work on Psychological and Mental Health
Epidemiological studies have been carried out over the past ten years have demonstrated the effects of night shift work on health.
According to these studies, shift workers experience nervousness, irritability, and anxiety as the consequences of most stressful working conditions. Due to the persistent disturbance of the circadian rhythm as well as a growing sleep deficit, work is my experience chronic fatigue, neuroticism, chronic anxiety, and depression, as well as mood disorders. As well as this, night shift workers also experienced higher absenteeism and some required treatment with psychotropic drugs including sedatives.
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The Effects of Night Shift Work on the Gastrointestinal System
Although the total quantity of food ingested by shift workers does not affect total energy intake, the frequency and timing of eating often differ. Moreover, night shift workers may sometimes consume foods with greater fat and carbohydrate content as a result of sleep deprivation, as well as snacking more frequently during short breaks.
After sleeping, between 20 and 75% of overnight shift workers versus 10 to 25% of day workers experience digestive troubles. These are associated with the mismatch between mealtimes and gastrointestinal functions which are determined by the circadian phase. These functions include basic creations of gastric, bile, and pancreatic fluids, the movement of the intestines, enzyme activity, rate of feed absorption in the intestine, and the release of hunger-associated hormones.
Moreover, night shift workers tend to ingest food of reduced quality and composition i.e., those with a higher preservative content, as seen in pre-packed and highly processed foods.
Night shift workers also tend to experience a greater frequency of gastrointestinal troubles and diseases compared to day workers. These vary from less severe which includes changes in bowel habits, poor digestion, flatulence, and heartburn – to more severe effects such as peptic ulcers, irritable bowel syndrome, and gastroduodenostomies. These experiences were recorded in past, predominantly cross-sectional, epidemiological studies which did not use a standardized form of diagnostic methods to determine these experiencing as well as not controlling for confounding factors such as age, smoking, and socioeconomic status.
The Effect of Shift Work on Metabolic Disorders
Collectively, obesity, elevated levels of triglycerides, reduced HDL cholesterol, increased fasting glucose, and high blood pressure comprises metabolic syndrome. Metabolic syndrome is an important risk factor for the development of type 2 diabetes and cardiovascular disease.
Several studies have reported a greater prevalence of metabolic disturbances in workers with night shifts. These include overweight and obesity, as well as increased triglycerides and total cholesterol levels. These effects are thought to be a result of a disturbed circadian rhythm, poor quality, and inconsistent sleep, digestive disturbances, as well as changes in lifestyle habits which include the quality and timing of meals as well as increased snacking. These effects are further exacerbated by the experience of disrupted social temporal patterns on psychological disturbances which include stress and experience of conflict.
Disrupted sleep patterns may also influence the efficiency of the liver and the kidney. This is important shift workers may be exposed to chemical substances are different times of the day and night. As a result, shift workers may experience a greater risk of intoxication or retention of harmful substances. In the 1984 Bhopal disaster (an industrial chemical leakage accident from a factory in Bhopal,Madhya Pradeshin India) thousands of non-adjusted shift workers died in their sleep relative to consistent night-shift workers who were only partially affected.
This illustrates the need to account for the level of environmental/biological exposure. These include, for example, modifications to the Threshold Limit Value (TLV), which determines a level of substance exposure to which a worker can be exposed in each shift without experiencing adverse effects.
The Effect of Shift Work on the Cardiovascular System and Cancer
There is a well-established body of research that suggests that there's a strong association between night shift work and the development of cardiovascular disorders; shift workers have on average, a 40% increased risk for ischemic heart disease compared to today's workers. Moreover, shift workers are more likely to participate in, or experience, lifestyle habits that are major cardiovascular risk factors, such as smoking, obesity, and elevated levels of total cholesterol.
It is important to note that a closer relationship between the two variables has not been established.
As with cardiovascular disease, there is a correlation but not necessarily a causative mechanism linking the development of cancer to night shift work period the information available that discusses is exposure to shift work is based on sporadic self-reported assessment or affiliation to a work sector in which shift work is prevalent. Additional information such as the number of night shifts per month, or per year, as well as the number of consecutive night shifts, and the length of duty periods are not reported.
References:
- Costa G. (1996) The impact of shift and night work on health. Appl Ergon. doi:10.1016/0003-6870(95)00047-x.
- Strohmaier S, Devore EE, Zhang Y, et al. (2018) A Review of Data of Findings on Night Shift Work and the Development of DM and CVD Events: a Synthesis of the Proposed Molecular Mechanisms. Curr Diab Rep. doi:10.1007/s11892-018-1102-5.
- Figueiro MG, White RD. (2013) Health consequences of shift work and implications for structural design. J Perinatol. doi:10.1038/jp.2013.7.
