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Health Impacts of Shift Work: A Comprehensive Review of Evidence

This review explores the health impacts of shift work, including definitions, prevalence, and characteristics of shift schedules. It delves into the evidence base, conceptual framework, and specific health impacts such as accidents, sleep disorders, and cardiovascular diseases. The review also discusses mechanisms, sleep quality, and factors exacerbating sleep disturbances related to shift work. Learn about the risks and implications of shift work on overall health and well-being.

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Health Impacts of Shift Work: A Comprehensive Review of Evidence

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  1. Health impacts of shift work: review of the evidence • Tuesday 16 October 2018, 1.00-5.00pm • Attlee Suite, Portcullis House Prof Derk-Jan Dijk, PhD, FRSB, FMedSci

  2. What do we mean by shift work? According to the Health and Safety Executive • Standard work schedule/standard daytime hours • A work schedule involving an activity during the day, commonly for a period of eight hours between 7.00 am and 7.00 pm. • There is no specific definition of shift work in law • Shift work means • A work activity scheduled outside standard daytime hours, where there may be a handover of duty from one individual or work group to another • A pattern of work where one employee replaces another on the same job within a 24-hour period • Alternative definition: • Start of work between 2pm and 6.30am

  3. Examples of shift work • Work during the afternoon, night or weekend, typically with periods of the work schedule outside standard daytime hours • Extended work periods of 12 hours or more, often associated with compressing the working week • Rotating hours of work • Split shifts, where work periods are divided into two distinct parts with several hours break in between • Overtime • Standby/on-call duties

  4. Typical Shift Work Schedules Characteristics/things to consider • Shift duration • 8-hour shifts • 12-hour shifts • Shifts longer than 12 hours • Variable shift lengths • Split shifts • Rest breaks within shifts • Shift pattern • Permanent shifts • Rotating shifts • Forward rotation • Backward rotation • Shift rotation • Fast rotation • Slow rotation • Shift timing • Night shifts • Early morning starts • Afternoon starts • Daytime shifts

  5. Prevalence of shift work? Depends on precise definition/varies by sector/ country https://www.eurofound.europa.eu/data/european-working-conditions-survey • UK employees working shifts • 22% • UK employees working at least one night shift per month • 22% • UK night workers (2017) • 3.2 million; 11.7%; [TUC report] • USA work time arrangements outside 6.00am - 6.00pm • 29% • 2009 RCN survey of the nursing workforce: • 57% worked shifts and of those • 58% internal rotation • 32% day shifts • 10% permanent night shifts U.S.: data from the 2010 National Health Interview Survey.

  6. https://www.eurofound.europa.eu/data/european-working-conditions-surveyhttps://www.eurofound.europa.eu/data/european-working-conditions-survey NL=14% UK=22% HR Croatia: 40%

  7. Health impact of shift work The Evidence Base 2016 • Based on • 38 meta-analyses • 24 systematic reviews • Narrative reviews • Articles outlining possible mechanisms

  8. Conceptual Framework Waking functioning/ Health Shift Work Light-Dark Cycle Sleep-Wake Cycle Circadian Photoreception Individual Circadian Homeostat Sleep-wake history Biological time Genetic variation Modified from: Dijk and Lockley 2002

  9. Health impact: Accidents & Sleepiness During shift (but may include commute) • Shift and night work and long working hours--a systematic review of safety implications • Wagstaff and SigstadScand J Work Environ Health. 201;37:173-85 • Shift work • Long Working Hours •  increase in accident rate ranged from 50%-100% • Sleepiness during shifts • Shift Work Sleep Disorder (International Classification of Sleep Disorders, 3rd Edition) • Insomnia/excessive sleepiness • Reduction of total sleep time • Present for at least three months • Prevalence: 10-23%

  10. Croydon tram crash 'caused by driver falling asleep and speeding' The final report into the accident said the driver could have fallen into a “microsleep” during a 49-second period when the tram was passing through three consecutive tunnels in the hours of darkness. Inspectors said it was possible a “sleep debt” accumulated by the driver, who was regularly sleeping less than six hours before waking up at 3.20am to go to work, could have made him fatigued.

  11. Sleepiness Akerstedt and Wright. Sleep loss and fatigue in shift work and shift work disorders Sleep Med Clin 2009 4:257-271

  12. Commute home Night shift Day shift Modified from Dijk, Duffy, CzeislerJ Sleep Res 1992

  13. Health impact: Sleep • Subjective sleep quality (during ‘shift’) • Non-refreshing • Awakening difficult •  Early morning shift • Sleep duration (during ‘shift’) • Short after night shift: [subjective 5h:51min; objective 5.0-5.5h] • Short before morning shift [subjective 6h:37min; objective 5.5-6.0h] • Long after evening shift [subjective 8h:12min] • Exacerbating factors: • Short recovery times between shifts • Fast rotation • When sleep during shift days and recovery days is considered • No strong evidence for chronic sleep loss • Chronic sleep disturbances (e.g. insomnia symptoms) • Risk Ratio: 1.16 [95% Confidence Interval 0.97-1.38]

  14. Health impact: Cardiovascular disease • Based on systematic review and meta-analysis of • 34 observational studies • More than 2 million people • Findings • Shift work associated with increased risk for • Myocardial infarction (Pooled RR: 1.23; 95%CI 1.15-1.31) • Ischaemic stroke (pooled RR: 1.05; 95%CI 1.01-1.09) • Highest risk associated with night shift (RR: 1.41) • Evening shift: not significantly related

  15. Health impact: Metabolic disorders • The Relationship Between Shift Work and Metabolic Risk Factors: A Systematic Review of Longitudinal Studies. Proper et al. Am J Prev Med. 2016 50:e147-e157 • Shift work is associated with • Obesity/weight gain • One estimate of RR: 1.14; 9%CI 1.01-1.28 • Impaired glucose tolerance • Shift work is associated with • Type 2 diabetes • 12 cohort studies, 226 652 participants • OR 1.12 (95% CI: 1.06-1.19) • 10 cohort studies • OR 1.15 (95% CI 1.08-1.22)

  16. Health impact: Cancer • Breast cancer • 2007 International Agency for Research on Cancer •  shift work probably increases the risk for breast cancer • Since 2007 • Three reviews conclude • Insufficient or limited evidence • Four reviews report that • Long exposure (> 20 years) associated with elevated risk for breast cancer • RRs and 95% CIs • 1.19 (1.05 to 1.35) • 1.20 (1.08 to 1.33) • 1.19 (1.08 to 1.32) • 1.06 (1.01 to 1.10)

  17. Health impact: Cancer • Prostate Cancer • Meta-analysis based on eight studies • Shift work is associated with increased risk for prostate cancer • RR 1.24; 95%CI: 1.05-1.46 • 2.8% increase in risk for each five year’s duration of night shift work • Colorectal cancer • Meta-analysis based on six studies • Night shift work is associated with increased risk for colorectalcancer • OR 1.32; 95% CI 1.12-1.55 • 11 % increase in risk for each five year’s duration of night shift work

  18. Health impact: VARIA • Areas of interest • Mortality • Cognitive decline • Depression • Multiple sclerosis • Quality of Life • Individual differences • Sex • Age • Chronotype

  19. Health impacts of shift work: review of the evidence • Conclusions • Shift work is associated with a variety of adverse health outcomes • Negative effects of shift work may be mediated by • Sleep disturbance • Circadian disturbance • Life style factors • Diet • Physical Activity • Etc.,

  20. Peripheral circadian rhythm disruption when sleep is mistimed In phase Out of phase In phase: 1,396 rhythmic ‘genes’; 6.4% Out of phase: 228 rhythmic ‘genes’; 1.0% These changes were observed despite melatonin and cortisol not being affected Night • Archer et al. PNAS 2014;111(6):E682-91

  21. Archer and Oster J Sleep Res 2016

  22. Health impacts of shift work: review of the evidence • Tuesday 16 October 2018, 1.00-5.00pm • Attlee Suite, Portcullis House Prof Derk-Jan Dijk, PhD, FRSB, FMedSci

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