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

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
Tuesday, 30 April 2019

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
Tuesday, 30 April 2019

4. Typical Shift Work Schedules
Characteristics/things to consider
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
Shift duration
8-hour shifts
12-hour shifts
Shifts longer than 12 hours
Variable shift lengths
Split shifts
Rest breaks within shifts
Tuesday, 30 April 2019

5. Prevalence of shift work?
Depends on precise definition/varies by sector/ country
UK employees working shifts
22%
UK employees working at least one night shift per month
UK night workers (2017)
3.2 million; 11.7%; [TUC report]
USA work time arrangements outside 6.00am pm
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.
Tuesday, 30 April 2019

6. https://www. eurofound. europa
NL=14%
UK=22%
HR Croatia: 40%
Tuesday, 30 April 2019

7. Health impact of shift work
The Evidence Base
2016
Based on
38 meta-analyses
24 systematic reviews
Narrative reviews
Articles outlining possible mechanisms
Tuesday, 30 April 2019

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

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 Sigstad Scand 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%
Tuesday, 30 April 2019

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.
Tuesday, 30 April 2019

11. Sleepiness
Akerstedt and Wright. Sleep loss and fatigue in shift work and shift work disorders Sleep Med Clin :

12. Night shift Day shift Commute home
Tuesday, 30 April 2019
Modified from Dijk, Duffy, Czeisler J 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 h]
Short before morning shift [subjective 6h:37min; objective h]
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 ]
Tuesday, 30 April 2019

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 )
Ischaemic stroke (pooled RR: 1.05; 95%CI )
Highest risk associated with night shift (RR: 1.41)
Evening shift: not significantly related
Tuesday, 30 April 2019

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 :e147-e157
Shift work is associated with
Obesity/weight gain
One estimate of RR: 1.14; 9%CI
Impaired glucose tolerance
Type 2 diabetes
12 cohort studies, participants
OR 1.12 (95% CI: )
10 cohort studies
OR 1.15 (95% CI )

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)
Tuesday, 30 April 2019

17. Health impact: Cancer OR 1.32; 95% CI 1.12-1.55
Prostate Cancer
Meta-analysis based on eight studies
Shift work is associated with increased risk for prostate cancer
RR 1.24; 95%CI:
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 colorectal cancer
OR 1.32; 95% CI
11 % increase in risk for each five year’s duration of night shift work
Tuesday, 30 April 2019

18. Health impact: VARIA Areas of interest Mortality Cognitive decline
Depression
Multiple sclerosis
Quality of Life
Individual differences
Sex
Age
Chronotype
Tuesday, 30 April 2019

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.,
Tuesday, 30 April 2019

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
Prof Derk-Jan Dijk, PhD, FRSB, FMedSci
Tuesday 16 October 2018, pm
Attlee Suite, Portcullis House