[4] There are numerous shift work schedules, and they may be permanent, intermittent, or rotating; consequently, the manifestations of SWSD are quite variable.

Many studies have associated sleep disorders with decreased bone mineral density (BMD) and risk for fracture.

Researchers have found that those who work long-term in night positions, like nurses, are at a great risk for wrist and hip fractures (RR=1.37).

[6] Obesity, diabetes, insulin resistance, elevated body fat levels[7] and dyslipidemias were shown to be much higher in those who work night shift.

[10] In the same article, the authors affirm that there is a high prevalence of sleepiness and symptoms of sleep disorders related to the circadian system in medical center nurses.

[1] Sleep loss seen in shift workers greatly impairs cognitive performance, being awake for 24 hrs.

[15] A field study investigating the nature of SWD in an experimental (with SWD) and control (non-SWD) group of Finnish shift workers revealed decreased total sleep time (TST) and increased sleep deficit before morning shifts.

[15] Many studies have shown evidence of how partial and total sleep deprivation affects work productivity, absenteeism, fatal workplace accidents, and more.

[16][17] In a study by Akkerstedt et al., those who had a hard time sleeping in the past two weeks were at a greater risk for having a fatal workplace accident (RR=1.89, 95% CI 1.22–2.94).

[18] Other sleep disorders, like OSA which are risk factors for SWSD, have also been associated with low productivity, absenteeism, and accidents.

[19] At a cognitive level, sleep deprivation has been shown to cause decreased attentiveness, increased micro-sleeps, delayed psychomotor response, performance deterioration, neglect of activities, decline in working memory, and more.

In a study by Naigi, et al., over the course of a shift, nurses exhibited decreasing levels of Natural Killer cells, an innate immune response that plays a role in infectious disease and tumor suppression.

Many studies have shown that prolonged sleeplessness and sleep disorders, such as OSA, increases systemic levels of CRP, a marker of cardiovascular disease.

[20] Many studies have shown that lack of sleep causes blood pressure to increase from the prolonged stimulation of the nervous system.

[27] Insomnia and wake-time sleepiness are related to misalignment between the timing of a non-standard wake–sleep schedule and the endogenous circadian propensity for sleep and wake.

In addition to circadian misalignment, attempted sleep at unusual times can be interrupted by noise, social obligations, and other factors.

This study is similar to the one done by the National Center for Biotechnology Information,[36] which found that their hypothesis of sleep deprivation and the cognitive impact it has on nurses was strongly supported in 69% of shift workers.

The impairment in cognitive performance, such as general intellect, reaction time, and memory, was statistically significant among the staff nurses due to poor sleep quality and decreased alertness while awake.

Shift work sleep disorder affects patient care within all aspects of the medical field.

They found that the main reason behind medication errors are stress, fatigue, increased workload, night shifts, nurse staffing ratio and workflow interruptions.

[38] The rhythms are maintained in the suprachiasmatic nucleus (SCN), located in the anterior hypothalamus in the brain, and synchronized with the day/night cycle.

[38] Gene-transcription feedback loops in individual SCN cells form the molecular basis of biological timekeeping.

[39] Photoreceptors located in the retina of the eye send information about environmental light through the retinohypothalamic tract to the SCN.

[28] Sleepiness is manifested as a desire to nap, unintended dozing, impaired mental acuity, irritability, reduced performance, and accident proneness.

[40] The symptoms coincide with the duration of shift work and usually remit with the adoption of a conventional sleep-wake schedule.

However, naps that are too long (over 30 minutes) may generate sleep inertia, a groggy feeling after awakening that can impair performance.

[45] In the transportation industry, safety is a major concern, and mandated hours of service rules attempt to enforce rest times.

For workers who want to use bright light therapy, appropriate fixtures of the type used to treat winter depression are readily available[47] but patients need to be educated regarding their appropriate use, especially the issue of timing.

[28] Night shift medical field workers report the highest activity, along with the least amount of sleep.

Hypnotics given in the morning can lengthen daytime sleep; however, some studies have shown that nighttime sleepiness may be unaffected.