Since the use of oil burning lamps, followed by the invention of the light bulb by Thomas Edison, there has been a steady growth of nocturnal work. With the increasing demand worldwide to sustain our 24-hour society, it has been estimated that nearly 20% of the labor force worldwide involves work shifts outside the traditional 8:00 AM to 5:00 PM workday (Valentina et al. Sleep. 2014;37[3]:545). Leading this trend is the United States (as seen in the Figure). Shift work is even common in occupations that directly affect the health and safety of others, such as transportation and health care.
Dr. Aneesa Das
Shift work can cause a disruption of our circadian sleep-wake pattern and can often lead to sleep deprivation. Shift work disorder (SWD) is established when this misalignment between the timing of the sleep/wake cycle causes sleep disturbance, insomnia, sleepiness, fatigue, and impaired daytime function. The 2008 Sleep in America Poll assessed sleep and the workplace. The poll found that 58% of shift workers (defined as workers who start their job after 6:00 PM but before 6:00 AM) reported less than 6 hours in bed on workdays compared with 13% of nonshift workers. Shift workers worked more hours per week, were more likely to have other sleep disorders, and were more likely to drive drowsy. Recently reported cross-sectional data from the population-based Survey of the Health of Wisconsin (SHOW), collected from 2008 to 2012, showed that shift workers are more commonly men, minorities, and with lower levels of education (Givens et al. Sleep Health. 2015;1:115).
Shift work is more prevalent in blue-collar workers. However, white-collar nocturnal work is increasing as well. According to the US Bureau of Labor Statistics, between 1991 and 1997, there was an 11% increase in the number of white-collar employees working nights compared with only a 6% increase among blue-collar employees (Mcmenamin, Monthly Labor Review. 2007;Dec:3).
Work hours in the United States and elsewhere.
(adapted from Hamermesh et al. 2014. Long work weeks and strange hours. National Bureau of Economic Research.)
A potential health risk
Shift workers and those with SWD may be at greater risk for many health concerns. The SHOW data found shift workers to be more overweight than traditional schedule workers and reported more sleep problems, such as insomnia symptoms, insufficient sleep, and sleepiness. Shift workers have an increased risk of sleep disorders, cardiovascular disorders, obesity, and cancer.
Dr. Soriano is with the Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine; The Ohio State University; Columbus, Ohio
Regarding cardiovascular disorders, shift work has been associated with coronary artery disease, hypertension, and cardiovascular death. The risk of death from heart disease was 19% higher among those who worked rotating night shifts for 6 to 14 years and 23% higher for those who worked rotating night shifts for 15 or more years according to the Nurses’ Health Study (Gu et al. Am J Prev Med. 2015;48[3]:241). While numerous studies have suggested higher prevalence of cardiovascular disease among shift workers, a clear causal pathway has not been established. Possible explanations for the increased cardiovascular disease include circadian stress along with behavioral changes, such as decreased physical activity and dietary changes in night shift workers. Shift work and sleep deprivation can lead to insulin resistance and type 2 diabetes, which can further increase cardiovascular risk. Other theories suggest physiologic stress, such as autonomic dysfunction, cortisol dysregulation affecting inflammation, or endothelial dysfunction.
Shift work has recently been associated with malignancy. Most notably, shift work has been associated with breast cancer. This risk appears to be greatest with prolonged rotating night shift early in one’s career (Schernhammer. Occup Environ Med. 2014;71[1 Suppl]:A121). The relationship between shift work and breast cancer is likely related to the changes in the circadian melatonin levels due to nocturnal exposure to light through multiple pathways (Hill et al. Endocr Relat Cancer. 2015;22[3]:R183). Recent data from the Nurses’ Health Study report a 25% increased risk of lung cancer among women working rotating shifts for more than 15 years compared with those working no night shifts. There is limited and inconsistent evidence for an association between shift work and prostate and colon cancers.
Irregular work hours not only result in physiologic stress but also psychosocial stress. With greater difficulties controlling personal hours, decrease work-life balance, and insufficient recovery sleep, family and social relationships are vulnerable to deterioration. This chronic “social jet lag” is associated with sleep deprivation, absenteeism, and depression.
Working during our circadian-predicted sleep phase can be associated with sleepiness at work. Risk for errors and accidents appear to be higher in shift workers with nearly three-fold increased risk of occupational and commute-to-home accidents compared with day workers (Swanson et al. J Sleep Res. 2011;20[3]:487). There is reported increased risk of motor vehicle accidents in health-care workers and police and commercial drivers working nights compared with those that do not work night shifts (Wright et al. Sleep Med Rev. 2013;17[1]:41). Risk of vehicular, aviation, and industrial accidents are highest at night, especially in the early morning hours.