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Discussion paper

doi:10.5271/sjweh.3920

Scand J Work Environ Health

Online-first -article

How to schedule night shift work in order to reduce health

and safety risks

Garde AH, Begtrup L, Bjorvatn B, Bonde JP, Hansen J, Hansen ÅM,

Härmä M, Jensen MA, Kecklund G, Kolstad HA, Larsen AD, Lie JA,

Moreno CRC, Nabe-Nielsen K, Sallinen M

This Discussion Paper provides scientifically based recommendations

on night shift schedules, including consecutive shifts, shift intervals

and duration, which may minimize health and safety risks.

Affiliation:

The National Research Centre for the Working

Environment, Lerso Parkallé 105, DK-2100 Copenhagen, Denmark.

[email protected]

Refers to the following texts of the Journal:

2012;38(4):380-390

2015;41(3):268-279 2010;36(2):121-133 2013;39(4):325-334

2018;44(4):403-413 2018;44(4):394-402 2018;44(4):385-393

2019;45(2):166-173 2019;45(3):256-266 2020;46(4):446-453

[online first; 09 June 2020] [online first; 07 July 2020]

Key terms:

cancer; cardio-metabolic disease; circadian disruption;

health; injury; night shift; night shift work; night work; pregnancy; risk;

safety; schedule; shift work; shift work schedule; shift worker; sleep

duration; sleep quality; sleepiness

This work is licensed under a

Creative Commons Attribution 4.0 International License.

Print ISSN: 0355-3140 Electronic ISSN: 1795-990X Copyright (c) Scandinavian Journal of Work, Environment & Health

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iscussion paper

Scand J Work Environ Health – online first. doi:10.5271/sjweh.3920

This work is licensed under a Creative Commons Attribution

4.0 International License.

How to schedule night shift work in order to reduce health and safety risks

by Anne Helene Garde, PhD,

1, 2

Luise Begtrup, PhD,

Bjørn Bjorvatn, PhD,

4, 5

Jens Peter Bonde, PhD,

2, 3

Johnni Hansen, PhD,

Åse

Marie Hansen, PhD, DMSc,

1, 2

Mikko Härmä, PhD,

Marie Aarrebo Jensen, PhD,

Göran Kecklund, PhD,

Henrik A Kolstad, PhD,

Ann

Dyreborg Larsen, PhD,

Jenny Anne Lie, PhD,

Claudia RC Moreno, PhD,

8, 11

Kirsten Nabe-Nielsen, PhD,

Mikael Sallinen, PhD

Garde AH, Begtrup L, Bjorvatn B, Bonde JP, Hansen J, Hansen ÅM, Härmä M, Jensen MA, Kecklund G, Kolstad HA, Larsen AD,

Lie JA, Moreno CRM, Nabe-Nielsen K, Sallinen M. How to schedule night shift work in order to reduce health and safety risks.

Scand J Work Environ Health

– online first. doi:10.5271/sjweh.3920

Objectives

This discussion paper aims to provide scientifically based recommendations on night shift schedules,

including consecutive shifts, shift intervals and duration of shifts, which may reduce health and safety risks.

Short-term physiological effects in terms of circadian disruption, inadequate sleep duration and quality, and

fatigue were considered as possible links between night shift work and selected health and safety risks, namely,

cancer, cardio-metabolic disease, injuries, and pregnancy-related outcomes.

relevant scientific literature within their main research area.

Method

In early 2020, 15 experienced shift work researchers participated in a workshop where they identified

Results

Knowledge gaps and possible recommendations were discussed based on the current evidence. The

consensus was that schedules which reduce circadian disruption may reduce cancer risk, particularly for breast

cancer, and schedules that optimize sleep and reduce fatigue may reduce the occurrence of injuries. This is

generally achieved with fewer consecutive night shifts, sufficient shift intervals, and shorter night shift duration.

and possibly breast cancer, night shift schedules have: (i) ≤3 consecutive night shifts; (ii) shift intervals of ≥11

hours; and (iii) ≤9 hours shift duration. In special cases – eg, oil rigs and other isolated workplaces with better

possibilities to adapt to daytime sleep – additional or other recommendations may apply. Finally, to reduce risk

of miscarriage, pregnant women should not work more than one night shift in a week.

Conclusions

Based on the limited, existing literature, we recommend that in order to reduce the risk of injuries

schedule; shift worker; sleepiness; sleep duration; sleep quality.

Key terms

cancer; cardio-metabolic disease; circadian disruption; injury; night work; pregnancy; shift work

In 2007 and again in 2019, the International Agency for

Research on Cancer (IARC) classified night shift work

as probably carcinogenic to humans (group 2A) based

on limited evidence of cancer in humans, sufficient

evidence of cancer in experimental

animals, and strong

mechanistic evidence in experimental animals (1). Night

shift work was defined as work of ≥3 hours between

23:00–06:00 hours and may be organized

in many

ways including 2- or 3-shift work, irregular schedules,

and permanent night shift work (2, 3). The 2007 IARC

evaluation prompted a workshop in Denmark resulting

in recommendations for the prevention of the effects of

night shift work on risk of breast cancer based upon the

available epidemiological, experimental and mechanistic

evidence at that time (4). Since then, numerous epide-

miological and experimental studies on different types

1 The National Research Centre for the Working Environment, Copenhagen, Denmark.

2 Department of Public Health, University of Copenhagen, Copenhagen, Denmark.

3 Department of Occupational and Environmental Medicine, Bispebjerg and Frederiksberg Hospitals, Copenhagen, Denmark.

Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.

5 Norwegian Competence Center for Sleep Disorders, Haukeland University Hospital, Bergen, Norway.

Danish Cancer Society Research Center, Copenhagen, Denmark.

Finnish Institute of Occupation Health, Helsinki, Finland.

Stress Research Institute, Department of Psychology, Stockholm University, Stockholm, Sweden.

9 Department of Occupational Medicine, Danish Ramazzini Centre, Aarhus University Hospital, Aarhus, Denmark.

10 National Institute of Occupational Health, Oslo, Norway.

11 School of Public Health, University of São Paulo, Sao Paulo, Brazil.

Correspondence to: Anne Helene Garde,

The National Research Centre for the Working Environment,

Lerso Parkallé 105, DK-2100 Copenhagen,

Denmark. [E-mail: [email protected]].

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Night shift schedules and health and safety risks

of cancer have been published. Furthermore, the risk of

other adverse health outcomes, such as cardiovascular

disease, diabetes, injuries and pregnancy-related out-

comes, have also been associated with night shift work.

The increasing amount of studies on shift work, health

and safety has prompted requests from policy-makers,

employers and employees for scientifically based rec-

ommendations on specific

ways to schedule night shift

work in order to reduce health and safety risks, which

extend previous recommendations on breast cancer to

other outcomes.

This paper aims to provide scientifically based rec-

ommendations on night shift schedules that reduce

health and safety risks. As outlined in figure 1,

night

shift schedules

included night shift intensity (number of

night shifts per unit time), consecutive night shifts (num-

ber of night shifts in a row), permanent night shift work

(primarily or only night shifts), shift intervals (time

between shifts), direction of rotation (typically forward,

eg, D → E → N, or backward rotation, eg, N → E →

D) and shift duration (number of hours in a shift). The a

priori selected

health and safety outcomes

were cancer,

cardio-metabolic disease, injuries and pregnancy-related

outcomes, such as miscarriage and pregnancy-related

hypertension and pre-eclampsia. These outcomes were

selected because of severity of the disease/event and

prior knowledge of studies expected to be informative.

Furthermore,

short term physiological effects

to circadian disruption, inadequate sleep duration and

quality, fatigue and sleepiness were considered as pos-

sible mechanisms linking night shift work to health and

safety risks and considered for further evidence in the

formulation of the given recommendations.

Figure 1.

Outline of

selected core shift

work schedules, po-

tential mechanisms

and selected out-

comes included in

the present work.

The recommendations were based on the literature on

night shift schedules and the a priori selected outcomes.

Evidence on short-term physiological effects was used

to substantiate the recommendations.

Results

Short-term physiological effects of night shift work on

health and safety risks

Circadian disruption.

Circadian rhythms in physiological

functions are pivotal for survival (5). They are primarily

synchronized to the light–dark cycle by light exposure

through the eyes, which excites the intrinsically pho-

tosensitive retinal ganglion cells (ipRGC). The ipRGC

are connected to the suprachiasmatic nucleus (SCN)

located in the hypothalamus (6). Virtually all cells

in the body have molecular clocks that are normally

synchronized by the master clock in the SCN. Projec-

tions from the SCN innervate the sympathetic nervous

system and other structures such as the pineal gland,

which regulates downstream peripheral oscillators via

humoral, endocrine, and neural signals, resulting in a

coherent time organization of bodily processes for opti-

mal performance (7). Melatonin is a hormone mainly

produced in the pineal gland under direct control of

the circadian timing system. Thus, melatonin produc-

tion is controlled by the light–dark cycle exposure, and

its plasma concentration signalizes this to virtually all

organs and tissues. Therefore, melatonin is essential

to maintain the internal circadian synchronization and

regulate the sleep–wake cycle.

In this paper, the term “circadian disruption” is used

in a broad sense to cover the changes in the circadian

Methods

Working within different fields of night shift work

and health and safety research and performing epide-

miological, observational or experimental studies, 15

experience shift work researchers participated in a 3-day

workshop held in January 2020 in Denmark. Prior to the

workshop, the participants identified the most relevant

scientific literature on the associations and possible

mechanisms between night shift work and health and

safety within their main research area. After the work-

shop, a supplementary literature search was performed

in PubMed. Furthermore, studies included in recent sys-

tematic reviews were checked for relevant information.

Cohort and case–control studies and meta-analysis that

assessed two or more doses or categories of a night shift

schedule were included. Cross-sectional studies and

studies that solely compared night shift work with day

or non-night work, eg, ever/never night, were excluded.

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Garde et al

rhythm such as amplitude, duration, and timing of

biological rhythms and objective or subjective proxies

of changed circadian rhythm (8). Circadian disruption

may, depending on intensity and duration, be caused by

a number of factors: light-at-night, altered sleep–wake

cycle (disturbed sleep), and other behaviors that alter the

peripheral clocks (9).

Night shift workers are exposed to light-at-night,

which has earlier been proposed as one of the exposures

linked with breast cancer through suppression of melato-

nin (10). Light-at-night is associated with lower levels of

melatonin in both experimental (11–13) and observational

studies of night shift workers compared with day work-

ers (14, 15). Animal studies show that alterations in the

light–dark schedule suppress melatonin (3). Furthermore,

some prospective cohort studies indicate that women with

higher levels of morning urinary melatonin metabolites

have a modestly lower risk of breast cancer (16, 17).

For optimal biological efficiency, key circadian

rhythms must maintain a certain phase relation to one

another and follow an internal order (7). Because different

organ tissues, biological systems and cells change their

rhythms with different speed, desynchronization between

internal circadian rhythms may develop as a consequence

of night shift work (18). Experimental evidence shows

that the internal desynchronization leads to an accelerated

growth of human breast tumor xenografts in mice (19).

The degree of desynchronization may depend on type

of night shift schedules, eg, suppression of melatonin

and changes in cortisol rhythms were influenced by the

number of increasing number of consecutive night shifts

among Danish male police officers (20).

Sleep duration and quality.

Night shift workers normally

sleep during the day, which is associated with short

sleep duration, insomnia symptoms such as premature

awakening and non-restorative sleep, and a reduction in

stage 2 and rapid eye movement (REM) sleep compared

with other shifts and days off (21–23). It is likely that

components of the shift schedule, for example number

of days off, intensity of night shift work, and frequency

of quick returns and early morning work, contribute

to chronic short sleep duration and insomnia (24). If

the night shift worker suffers from shift work disorder,

defined as having shift work-related sleep problems and/

or excessive sleepiness, one would assume that the sleep

disturbances are chronic. The prevalence of shift work

disorder is higher among night shift workers than shift

workers who alternate between day and evening work,

and shift work disorder is also positively correlated with

frequency of night shifts in the shift schedule (25, 26).

Chronic short sleep duration (≤6 hours per day), par-

ticularly when associated with insomnia complaints, has

been associated with cardiovascular disease and type-2

diabetes (27, 28) and could be a mechanism linking

night shift work with these adverse health outcomes. It

has also been hypothesized that short sleep duration may

increase cancer risk and that long sleep may reduce breast

cancer, but findings are inconsistent (29). However, to the

best of our knowledge, no prospective study has evalu-

ated whether shift work disorder or chronic short sleep

duration among night shift workers increase the risk of

developing cardio-metabolic diseases and cancer.

Fatigue and sleepiness.

Fatigue and sleepiness, particu-

larly related to sleep restriction, have been suggested

as plausible mechanisms linking night shift work and

injury through impaired performance and alertness

(30). Sleepiness, defined as increased sleep pressure,

has been shown to rise while working during the night

and may depend on the night shift schedule. The most

consistent result is that sleepiness is most profound on

the first night shift in both experimental and observa-

tional studies (31–38). Also, slowly backward-rotating

shift systems (which have several consecutive shifts and

sometimes short shift intervals) have been found to be

associated more strongly with sleepiness on night shifts

than fast forward-rotating systems (39). Furthermore,

there are indications that alertness and performance are

impaired on 12-hour night shifts compared with 8-hour

shifts (40, 41), although later studies did not find such

an effect on sleep or sleepiness (39).

Taken together, night shift work has several short-

term physiological effects: circadian disruption is intro-

duced, levels of melatonin are modestly suppressed,

circadian rhythms are desynchronized, sleep duration

is reduced, and sleepiness is increased. The short-term

physiological effects appear to depend on how the night

shifts are scheduled (20, 25, 26, 31–38). The short-

term physiological effects are suggested to link night

shift work to acute safety risks and possibly long-term

health effects, although studies specifically addressing

whether these acute effects serve as mediators of long-

term health and safety risks are lacking.

Scheduling of night shift work and risk of cancer, cardio-

metabolic disease and injuries

Studies of night shift intensity, consecutive night shifts,

shift intervals, and duration of shift in relation to risk of

cancer, cardio-metabolic disease and injuries are sum-

marized in tables 1–3. In table 4, results from studies on

pregnancy-related outcomes are presented.

Intensity of night shifts.

Intensity of night shift work,

which is often operationalized as number hours or night

shifts per unit of time, has been suggested as important

parameter in epidemiological studies (2, 42). Studies

have used different measures of intensity, eg, night

shift hours per week (43), lifetime mean night shifts

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Night shift schedules and health and safety risks

Table 1.

Studies on intensity of night shifts and number of consecutive night shifts and risk of cancer, cardio-metabolic disease and injuries. [NA=not

available; CI=confidence interval.]

Study

Davis, Mirick, &

Stevens, 2001 (43)

Study design

Case–control study

(1993–1995)

Outcome

Breast cancer

Exposure

Night work hours/week (avg. of 10 year period)

<1.2

1.2–2.7

2.7–5.7

≥5.7

Never night work

<5 years night shift with # of consecutive shifts:

≥3

≥4

≥5

≥6

≥7

≥5 years night shift with # of consecutive shifts:

≥3

≥4

≥5

≥6

≥7

Years with ≥3 night shifts/month

Never night work

Never ≥3 night shifts/month

1–14

15–29

≥30

Consecutive night shifts/week

1–2

≥3 for 1–5.9 years

≥3 for 6–14.9 years

≥3 for ≥15 years

Consecutive night shifts

Premenopausal women

Night shifts/week

Never

1–2

≥3

Postmenopausal women

Night shifts/week

Never

1–2

≥3

Cases

713

102

194

160

137

119

109

278

131

102

390

152

1393

108

2979

146

Risk

1.3

1.4

1.5

2.3

1.1

1.2

1.1

1.4

1.6

1.8

1.7

1.4

1.2

0.8

1.0

1.1

2.1

2.5

1.05

1.16

1.36

1.31

1.03

1.80

0.73

1.01

0.92

95% CI

Reference

0.5–3.1

0.6–3.2

0.6–3.6

1.0–5.3

Reference

0.8–1.6

0.8–1.7

0.8–1.6

0.8–1.5

0.9–1.9

1.0–2.4

1.1–2.8

Reference

0.8–2.6

0.9–1.6

0.9–1.7

0.5–1.4

Reference

0.5–1.9

0.5–2.3

1.0–4.8

1.0–6.6

Reference

0.92–1.21

0.96–1.40

1.14–1.62

Reference

0.89–1.93

0.78–1.36

1.20–2.71

Reference

0.51–1.03

0.79–1.29

0.65–1.31

Continues

Lie et al, 2011 (49)

Nested case–

control study of

nurses (1990–2007)

Breast cancer

Hansen & Lassen,

2012 (45)

Nested case–control

Breast cancer

study of military

employees (1990–2003)

Fischer et al 2017

(51)

Meta-analysis

Occupational

injuries

Cordina-Duverger et

Pool of five harmonized

al, 2018 (46)

case–control studies

(2004–2013)

Breast cancer

per month (44), mean number of night shifts per week

in periods with night shift work (45, 46) (table 1). Due

to the large variation in the used metrics and exposure

time windows, the consistency of results across studies

cannot be evaluated, although generally, high intensity

appears to be associated with higher risk of breast cancer

(43, 45, 46), hypertension (47) and diabetes (44), but

not injuries (48) (table 1).

Number of consecutive night shifts.

Number of consecu-

tive night shifts, ie, the number of night shifts in a

row represents a specific case of intensity. Working ≥5

consecutive night shifts for ≥5 years has been associated

with higher risk of breast cancer in nurses from Norway

(49). Similarly, female military employees who had ≥3

consecutive night shifts for ≥6 years had higher breast

cancer risk (45). Working ≥6 consecutive night shifts

have been associated with a higher risk of prostate

cancer, particularly in combination with long shifts,

among permanent night but not rotating shift workers

(50). In a meta-analysis based on eight studies mostly

in industry, the risk of occupational injuries was studied

on the first, second, third and fourth consecutive night

shift. It was found that the risk increased with increasing

number of consecutive night shifts and was highest on

the fourth consecutive night shift (51). However, among

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Garde et al

Table 1.

Continued.

Study

Study design

Wendeu-Foyet et al, Case-control study

2018 (50)

(2012–2014)

Outcome

Prostate cancer

Exposure

Never night work

Permanent night workers

Consecutive night shifts

≥6

Cases

532

Risk

1.01

1.33

0.54

0.58

0.60

2.57

95% CI

Reference

0.74–1.39

0.95–1.87

0.27–1.09

0.32–1.07

0.16–2.15

1.31–5.06

Vetter et al,

2018 (44)

Cohort study

(2006–2015)

Type 2 diabetes

Nielsen et al,

2018 (48)

study of hospital em-

ployees in Denmark

(2007–2015)

Injuries

Ferguson et al,

2019 (47)

Cohort study of alumi-

num manufacturing

workers (2003–2013)

Hypertension

Härmä et al

2020 (52)

Injuries

crossover study of hospi-

tal employees in Finland

(2003–2015)

Shift length (hour) for number of consecutive nights

≤10 for <6

≤10 for ≥6

>10 for <6

>10 for ≥6

Rotating night workers

Consecutive night shifts

≥6

Shift length (hour) for number of consecutive nights

≤10 for <6

≤10 for ≥6

>10 for <6

>10 for ≥6

Current type of night shift work

Day work

5173

Shift work with no/rare nights

730

Rotating shifts with some nights

461

Rotating shifts with usual nights

169

Average lifetime night shifts/month

804

3–8

125

210

Night shifts in a week

2161

603

352

171

≥5

Average % night shifts/month in the past year

>0–5

>5–50

>50–95

>95–100

Night shifts in a week

18837

830

920

409

209

125

0.77

0.98

0.72

0.93

1.24

1.36

1.11

1.13

1.37

1.16

1.02

1.21

1.12

1.02

0.95

1.00

1.08

2.47

2.40

3.21

3.71

1.03

1.12

0.94

0.85

0.87

0.81

0.53–1.11

0.56–1.74

0.49–1.06

0.50–1.71

0.44–3.55

0.29–6.26

Reference

1.02–1.22

1.01–1.22

1.13–1.65

Reference

0.83–1.58

0.82–1.26

1.02–1.45

Reference

0.98–1.28

0.88–1.17

0.80–1.12

0.78–1.30

0.73–1.59

Reference

1.12–5.44

1.04–5.55

1.32–7.80

1.24–11.09

0.97–1.10

1.01–1.23

0.85–1.03

0.74–0.98

0.70–1.08

0.59–1.12

hospital employees, the number of occupational injuries

increased only in connection with one night shift during

the past week (52). This finding can be explained by

sleepiness being most profound on the first night shift

as observed in both experimental and observational stud-

ies (31–38). Thus, the risk for injuries in relation to the

number of consecutive night shift may depend on other

shift characteristics, but at least in industry the risk has

been shown to increase after three consecutive nights.

Taken together, the results indicate that a maximum of

three consecutive night shifts implies a lower risk of

accidents and possibly cancer compared with more than

three consecutive night shifts.

There are examples of night shift schedules, which

involve many consecutive night shifts, eg, work on

offshore oil platforms (7–14 consecutive nights) and

work at remote places like Spitsbergen (21 consecutive

nights), which show that circadian adaptation to night

shift work appears to happen within days when it comes

to subjective and objective measures of sleep (53–55)

and cortisol rhythm (56). It is, however, not possible

from the current literature to assess the long-term health

and safety risk in these types of work settings. Thus, in

special cases, eg, oilrigs and other isolated workplaces

with better possibilities to adapt to daytime sleep, addi-

tional or other recommendations may apply.

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Night shift schedules and health and safety risks

Permanent night shift work.

Permanent night shift work is

characterized by having primarily or only night shifts

and therefore many night shifts per week or month. It has

been argued that employees with permanent night shift

work adjust to day time sleep and therefore do not expe-

rience circadian disruption. However, only a very small

minority of permanent night shift workers show complete

adjustment of their endogenous circadian rhythm to night

shift work (56, 57). We assume permanent night shift

workers have health risks that are similar to workers on

rotating night shift work with the addition of the potential

effect of high intensity and number of consecutive night

shifts. Because permanent night shift work is relatively

rare, most of the existing studies that have included this

work schedule are underpowered. Yet, permanent night

shift work is associated with risk of breast and prostate

cancer in some studies (50, 58) but not others (59, 60).

The scheduling of permanent night shift work varies in

duration of shifts, number of consecutive shifts and shift

intervals. For this reason, the health risk associated with

permanent night shift work per se cannot be evaluated

without more detailed exposure information. Indeed in a

study including such details, risk of prostate cancer was

only higher among permanent night shift workers with

long shifts and ≥6 consecutive night shifts (50).

Shift intervals.

Shift intervals of <11 hours between two

shifts (quick returns) have been associated with an

increase in injuries (52, 61, 62). Furthermore, evidence

of a 5% increase in injuries for each hour less between

two shifts has been shown (61). The results further

indicate that the risk of injuries may be particularly

increased after a quick return following a night shift (52,

61). In addition, a reduction in the number of annual

quick returns reduced the risk, whereas an increase was

associated with increased risk of self-reports of causing

harm to one-self or patients/others (62). The available

studies on shift intervals and occupational injuries indi-

cate that risk of injury is reduced when quick returns

are reduced and shift intervals are ≥11 hours (table 2).

Direction of rotation.

In animal studies, the central circa-

dian cycle is quicker to adjust when mimicking forward-

rotation schedules, eg, D →E →N, than backward

rotation, eg, N →E →D, and re-entrainment of most

variables is slower for phase advance than phase delay

(7). In several reviews, it has been concluded that shift-

ing from backwards to forward rotation improves sleep

(24, 39, 63), and an intervention study shows that fast

forward rotation was associated with lower triglyceride

and serum glucose and mean systolic blood pressure

(64). Furthermore, forward rotation usually implies

longer breaks (≥24 hours) when changing from one type

of shift to another, whereas backward-rotation systems

often imply breaks corresponding to only the duration

of the shifts, and therefore may have quick returns (65).

Taken together, forward-rotating schedules appear to

have the most advantages. However, a few studies with

Table 2.

Studies on shift intervals and risk of injuries.

[CI=confidence interval.]

Study

Nielsen et al,

2019 (61)

Study design

cohort study of

hospital employ-

ees in Denmark

(2008–2015)

Outcome

Injuries

Exposure

Time between shifts (hours)

1–2

3–5

6–8

9–11

12–14

15–17

Quick return (6–11 hours) before a:

Day shift

Evening shift

Night shift

1–34 quick returns/year at baseline and follow–up

Increase from 1–34 to >35 quick returns/year

>35 quick returns/year at baseline and follow–up

Decrease from >35 to 1–34 quick returns/year

1–34 quick returns/year at baseline and follow–up

Increase from 1–34 to >35 quick returns/year

>35 quick returns/year at baseline and follow–up

Decrease from >35 to 1–34 quick returns/year

Number of quick returns in the preceding 7 days

Quick return (<11 hours) before a:

Morning shift

Evening shift

Cases

116

107

232

4597

327

120

148

271

120

148

271

17 638

159

770

1890

Risk

1.52

2.24

1.36

1.32

1.24

1.32

0.91

2.58

0.35

8.49

0.27

0.96

0.64

0.83

0.98

1.15

1.05

1.68

95% CI

0.94–2.45

1.42–3.53

1.13–1.64

1.09–1.60

1.09–1.41

Reference

0.94–1.85

0.70–1.17

Reference

0.71–9.34

Reference

0.16-0.73

Reference

2.79–25.87

Reference

0.12-0.59

0.85-1.08

0.43-0.94

0.61-1.13

0.78-1.24

1.01-1.30

0.98-1.12

0.66–4.64

Vedaa et al, 2020

(62)

Longitudinal cohort

study of nurses

(2016–2018)

Harmed

oneself

Harmed

patients

Härmä et al 2020

(52)

crossover study of

hospital employees in

Finland (2003–2015)

No studies on cancer and cardio-metabolic diseases were found.

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Garde et al

prostate cancer as an outcome, which address direction

of rotation and the selected outcomes, found no associa-

tions (50, 66). For this reason, the risks of forward and

backward rotation in relation to cancer, cardio-metabolic

diseases and injuries cannot be evaluated based on the

current literature.

Duration of night shifts.

A meta-analysis based on four

studies found that risk of injury was increased with

shifts lasting 10 versus 8 hours (51). A register study

of hospital employees reported an increased risk for

occupational injuries in shifts lasting ≥12 hours (52). A

large study with pooled data from case–control studies

with complete work history in five countries, found a

higher risk of breast cancer in pre-menopausal (but not

post-menopausal) women working night shifts lasting

≥10 hours compared with women working night shifts

lasting <8 hours (46). Night shifts lasting >10 hours

were associated with higher risk of prostate cancer,

particularly when part of permanent night shift work

and ≥6 consecutive night shifts (50). These results sup-

port that risk of injury and possibly cancer are reduced

with night shifts schedules, which have shifts with a

maximum duration of 9 hours (table 3).

Pregnancy-related outcomes.

Melatonin is also produced in

the placenta (67) and may play a pivotal role in proper

placenta function and parturition (68, 69). Meta-anal-

yses of several large high-quality prospective studies

indicate that the risk, if any, of preterm birth and growth

Table 3.

Studies on daily duration of shifts and risk of cancer and injuries.

[NA=not available; CI=confidence interval.]

Study

Fischer et

al, 2017 (51)

Study design

Review and

meta-analysis

Outcome

Occupational

injuries

Exposure

Shift length (hours)

>12

Pre-menopausal women

Length of night shift (hours)

Never night work

8–9

≥10

Post-menopausal women

Length of night shift (hours)

Never night work

8–9

≥10

Never night work

Permanent night workers

Length of night shift (hours)

8–10

>10

Shift length (hours) for number consecutive nights

≤10 for <6

≤10 for ≥6

>10 for <6

>10 for ≥6

Rotating night worker

Length of nigh shift (hours)

8–10

>10

Shift length (hours) for number consecutive nights

≤10 for <6

≤10 for ≥6

>10 for <6

>10 for ≥6

Average hours worked per night (hours)

≥7

Duration of shifts (hours)

≥12

Cases

1669

111

167

3652

213

177

532

1845

103

440

Risk

1.06

1.54

1.51

1.77

2.73

1.03

1.20

1.36

1.09

1.12

0.96

0.32

0.86

1.88

0.54

0.58

0.60

2.57

0.42

0.79

1.29

0.72

0.93

1.24

1.36

1.04

0.96

1.23

95% CI

Reference

0.69–1.63

1.30–1.83

1.30–1.74

1.50–2.07

2.02–3.69

Reference

0.65–1.64

0.91–1.60

1.07–1.74

Reference

0.73–1.65

0.92–1.36

0.78–1.19

Reference

0.16–0.64

0.48–1.53

1.08–3.26

0.27–1.09

0.32–1.07

0.16–2.15

1.31–5.06

0.11–1.57

0.56–1.12

0.54–3.07

0.49–1.06

0.50–1.71

0.44–3.55

0.29–6.26

Reference

0.84–1.28

0.78–1.17

1.06–1.42

Cordina-Duverger

Pool of five harmo-

Breast cancer

et al, 2018 (46)

nized case-control

studies (2004–2013)

Wendeu-Foyet

et al, 2018 (50)

Case–control study

(2012–2014)

Prostate cancer

Jones et al, 2019

(88)

Cohort study

(2003–2014)

Breast cancer

Härmä et al 2020

(52)

crossover study of

hospital employees in

Finland (2003–2015)

No studies on cardio-metabolic disease were found.

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Night shift schedules and health and safety risks

restriction due to night shift work is marginal (70). The

evidence with respect to miscarriage has been more

limited but has indicated a higher risk especially with

permanent night shift work (71). Knowledge regarding

risk of pregnancy-related hypertension has been limited

(71). Recently, a large nationwide cohort study of health

professionals using payroll data, including exact work-

ing hours during pregnancy, found a dose-dependent

higher risk of miscarriage in women working

≥2 night

shifts the previous week (72). In the same cohort, the

risk of calling in sick within two days following night

shifts was higher throughout pregnancy independent of

individual factors and time-invariant confounders (73),

and – among night shift workers – the risk of hyperten-

sive disorders of pregnancy, including pre-eclampsia,

grew with increasing number of consecutive night shifts,

particularly among obese women (body mass index ≥30

kg/m

) (74). The results support that, in order to reduce

risk of miscarriage,

pregnant women should have no

more than one night shift in a week (table 4).

Recommendations and concluding remarks

We concluded that schedules that reduce circadian

disruption may reduce cancer risk, particularly breast

cancer, and schedules that optimize sleep duration and

quality and reduce fatigue may reduce the occurrence

of injuries. These changes in short-term physiological

Table 4.

Studies on night shift schedules and pregnancy-related outcomes. [GW=gestational week; NA=not available; CI=confidence interval.]

Study

Hammer et al,

2018 (74)

Study design

cohort study of

hospital employ-

ees in Denmark

(2007–2013)

Outcome

Pregnancy-related

hypertensive

disorders (incl.

pre-eclampsia)

Exposure

Duration of night shifts (hours)

<12

≥12

Number of consecutive night shifts

2-3

≥4

Number of quick returns

2-3

≥5

Number of night shifts the first 20 pregnancy weeks

1–19

≥20

Night shifts the previous week

≥2

Number of consecutive night shifts during pregnancy

≥2

≥3

≥4

≥5

≥6

≥7

Quick returns

In 2

trimester (13–22 GW)

Duration of night shifts (hours)

≤8

Number of night shifts

1–12

≥13

Number of consecutive night shifts

2–3

≥4

Number of quick returns

1–2

≥3

Day shifts

After a night shifts in:

trimester

Duration of night shifts (hours)

≤8

>8–12

>12

Cases

214

212

132

205

128

203

360

1521

167

201

438

261

Risk

1.08

1.22

1.41

1.12

1.07

1.15

1.00

1.18

1.05

1.09

1.16

1.29

1.51

1.68

1.02

95% CI

Reference

0.85–1.36

Reference

0.92–1.62

1.01–1.98

Reference

0.87–1.45

0.79–1.46

Reference

0.86–1.52

Reference

0.85–1.18

1.01–1.37

0.98–1.13

0.98–1.22

0.97–1.38

0.99–1.67

1.01–2.29

0.78–3.79

0.85-1.0

Begtrup et al,

2019 (72)

Cohort study of

Danish public hos-

pital employees

(2007–2013)

Miscarriage

Specht et al,

2019 (89)

cohort study of

hospital employ-

ees in Denmark

(2007–2013)

Pre-term birth

207

171

320

106

186

122

188

0.83

1.01

1.16

0.98

1.19

0.81

1.28

1.27

1.13

1.20

1.02

1.55

Reference

0.64–1.04

Reference

0.73–1.37

Reference

0.85–1.61

0.68–1.42

Reference

0.85-1.64

0.61–1.06

Reference

1.19–1.37

1.17–1.39

0.96–1.33

1.12–1.30

0.93–1.10

1.43–1.69

Hammer et al,

2019 (73)

National register-

Calling in sick

based cohort study within 2 days

of Danish workers in after a night shift

public administra-

tion and hospitals

(2007–2013)

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Garde et al

effects are generally achieved with fewer consecutive

night shifts, sufficient shift intervals, and shorter night

shift duration. Yet, sleepiness and possibly injury risk

may be increased during the first night shift.

Based on the limited, existing literature, we recom-

mend that in order to reduce the risk of injuries and

possibly breast cancer, night shift schedules have (i) ≤3

consecutive night shifts, (ii) shift intervals of ≥11 hours

and (iii) ≤9 hours shift duration.

In special cases, eg, oilrigs and other isolated work-

places with better possibilities to adapt to daytime sleep,

other recommendations may apply.

Finally, in order to reduce risk of miscarriage, preg-

nant women should have no more than one night shift

in a week.

The risk associated with intensity, permanent night

shift work and direction of rotation could not be evalu-

ated based on the included studies. However, high inten-

sity appeared to be associated with higher risk of breast

cancer, hypertension and diabetes, and knowledge from

physiological and experimental studies are in favor of

forward rotation.

Generally, major knowledge gaps were observed and

the number of studies on specific night shift schedules in

relation to risk of cancer, cardio-metabolic diseases and

injuries is limited. Concerning cancer, the majority of

studies are related to breast cancer and, to some extent,

prostate cancer. There is little evidence that results from

these studies are transferable to other cancer types or

from one sex to the other. Nor is it known if the short-

term physiological effects per se are associated with

long-term health and safety risk.

There are individual differences in response to night

shift work, eg, according to age and chronotype (ie, how

the circadian system embeds itself into the 24-hour day).

Advanced ageing is associated with earlier chronotype

(75), alterations in circadian rhythmicity and sleep–wake

homeostasis (76), and higher morbidity and mortality in

general. Ageing is, however, not associated with higher

sleepiness in general (77) or in relation to sleepiness in

night shift work (78). Due to the earlier chronotype and

decreased sleep efficiency, sleeping especially after the

nights shifts is curtailed (79). Besides the night shifts,

also quick returns are associated with increased risk for

sleep problems and fatigue among those aged ≥50 (80).

The present recommendations are related to the

selected night shift schedules deemed relevant for health

and safety. However, there are scheduling components

related to night shift work that were not covered by

the expert group – such as shift start and finish times

and employees’ control over night shift work. Also, the

specific characteristics of night shift schedules were

treated as if they were independent. However, the char-

acteristics are highly correlated, eg, longer shift duration

often implies fewer shifts and therefore more recovery

time. More research is needed to establish how the dif-

ferent schedule characteristics interact and affect health

and safety risks and if specific combinations imply a

particularly higher or lower risk to health and safety. To

make this possible, future etiological studies on shift

work and health need to be based on precise and prefer-

ably repeated information on exposure combined with

long, preferably registry-based follow-up. The use of

like payroll data, is recommended if a sufficient propor-

tion of working life is covered (81).

Although not systematic, the review of the litera-

ture aims to reduce bias in the selection of articles by

employing a bibliographic search strategy and having

a clear strategy for selection of papers. Several of

the presented studies are based on hospital workers

in the Nordic countries. Therefore, studies from other

countries and sectors should be performed to take into

account, eg, traditions regarding organization of night

shift work, contextual factors such as working condi-

tions and latitude-dependent exposure to sunlight over

the year, work tasks, and the organization of the health

care and welfare system.

Sleepiness is most profound on the first night shift.

Accordingly, sleepiness is an inevitable consequence

of working at night, no matter how night shifts are

scheduled as long as employees change to night-time

sleep during days off. Therefore, the concept of fatigue

risk management, covering also sleepiness countermea-

sures other than optimal shift scheduling (eg, use of

prior-sleep-wake data, fatigue detection technologies,

and fatigue proofing strategies) has been introduced

(82). Indeed, there are other ways to counteract the

adverse health and safety risks of night shift work than

through shift scheduling. At workplace level, fatigue

risk management (82), lighting conditions (83) and

self-rostering according to personal preference (84, 85)

could be applied. There is some research supporting

countermeasures at the individual level, such as bright

light, melatonin, naps, use of stimulants, as a means to

improve adaptation to night shift work (86). However,

there is so far little evidence that such countermeasures

reduce the long-term health consequences of night shift

work (86). Lastly, other outcomes such as work–life

balance and social well-being (87), productivity and

patient safety may be relevant to consider when sched-

uling night shifts.

Acknowledgement

NordForsk, Nordic Program on Health and Welfare

[grant number 74809] partly funded the writing of this

paper.

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Night shift schedules and health and safety risks

References

Ward EM, Germolec D, Kogevinas M, McCormick D,

Vermeulen R, Anisimov VN et al.; IARC Monographs Vol

124 group. Carcinogenicity of night shift work.

Lancet

Oncol 2019 Aug;20(8):1058–9.

https://doi.org/10.1016/

S1470-2045(19)30455-3.

Härmä M, Ropponen A, Hakola

Koskinen A, Vanttola

P, Puttonen

et al. Developing register-based measures

for assessment of working time patterns for epidemiologic

studies.

Scand J Work Environ Health 2015 May;41(3):268–

79.

https://doi.org/10.5271/sjweh.3492.

IARC Working Group on the Identification of Carcinogenic

Hazards to Humans. Night Shift Work. Lyon: International

Agency for Research on Cancer; 2020.

Bonde

JP, Hansen J, Kolstad HA, Mikkelsen

Olsen JH,

Blask DE et al. Work at night and breast cancer--report

on evidence-based options for preventive actions.

Scand

J Work Environ Health 2012 Jul;38(4):380–90.

https://doi.

org/10.5271/sjweh.3282.

Buijs RM, van Eden CG, Goncharuk VD, Kalsbeek

A. The biological clock tunes the organs of the body:

timing by hormones and the autonomic nervous system. J

Endocrinol 2003 Apr;177(1):17–26.

https://doi.org/10.1677/

joe.0.1770017.

Hattar

S, Liao

HW, Takao M,

Berson

DM, Yau KW.

Melanopsin-containing retinal ganglion cells: architecture,

projections, and intrinsic photosensitivity.

Science

2002 Feb;295(5557):1065–70.

https://doi.org/10.1126/

science.1069609.

Haus EL, Smolensky MH. Shift work and cancer risk:

potential mechanistic roles of circadian disruption,

light at night, and sleep deprivation. Sleep Med Rev

2013 Aug;17(4):273–84.

https://doi.org/10.1016/j.

smrv.2012.08.003.

Vetter C. Circadian disruption: what do we actually

mean?

Eur J Neurosci 2020 Jan;51(1):531–50.

https://doi.

org/10.1111/ejn.14255.

Kecklund G, Axelsson J. Health consequences of shift work

and insufficient sleep. BMJ 2016 Nov;355:i5210.

https://doi.

org/10.1136/bmj.i5210.

circadian disruption in humans and animal models.

Chronobiol Int 2014 Dec;31(10):1239–46.

https://doi.org/1

0.3109/07420528.2014.957302.

14. Daugaard

Garde AH,

Bonde

JP, Christoffersen J,

Hansen AM, Markvart J et al. Night work, light exposure

and melatonin on work days and days off. Chronobiol Int

2017;34(7):942–55.

https://doi.org/10.1080/07420528.201

7.1327867.

15. Papantoniou

Pozo OJ, Espinosa A, Marcos J, Castaño-

Vinyals G, Basagaña

et al. Circadian variation of

melatonin, light exposure, and diurnal preference in day

and night shift workers of both sexes. Cancer Epidemiol

Biomarkers Prev 2014 Jul;23(7):1176–86.

https://doi.

org/10.1158/1055-9965.EPI-13-1271.

16. Veiga ECA,

Simoes

R, Valenti VE, Cipolla-Neto J, Abreu

LC,

Barros

EPM, et al. Repercussions of melatonin on the risk

of breast cancer: a systematic review and meta-analysis. Rev

Assoc Med Bras (1992). 2019;65(5):699–705.

17.

Schernhammer

ES,

Berrino

F, Krogh V,

Secreto

G, Micheli

A, Venturelli E et al. Urinary 6-Sulphatoxymelatonin levels

and risk of breast cancer in premenopausal women: the

ORDET cohort. Cancer Epidemiol Biomarkers Prev 2010

Mar;19(3):729–37.

https://doi.org/10.1158/1055-9965.EPI-

09-1229.

18. Zelinski EL, Deibel SH, McDonald RJ. The trouble with

circadian clock dysfunction: multiple deleterious effects on

the brain and body. Neurosci Biobehav Rev 2014 Mar;40:80–

101.

https://doi.org/10.1016/j.neubiorev.2014.01.007.

19. Haus E, Smolensky M. Biological clocks and shift work:

circadian dysregulation and potential long-term effects.

Cancer Causes Control 2006 May;17(4):489–500.

https://

doi.org/10.1007/s10552-005-9015-4.

20. Jensen MA, Hansen AM,

Kristiansen

J, Nabe-Nielsen

Garde AH. Changes in the diurnal rhythms of cortisol,

melatonin, and testosterone after 2, 4, and 7 consecutive

night shifts in male police officers. Chronobiol Int

2016;33(9):1280–92.

https://doi.org/10.1080/07420528.20

16.1212869.

21. Flo E, Pallesen

Åkerstedt

Magerøy

Moen BE,

Grønli J et al. Shift-related sleep problems vary according

to work schedule. Occup Environ Med 2013 Apr;70(4):238–

45.

https://doi.org/10.1136/oemed-2012-101091.

22. Garde AH, Nabe-Nielsen

Jensen MA,

Kristiansen

Sørensen JK, Hansen ÅM. The effects of the number of

consecutive night shifts on sleep duration and quality.

Scand

J Work Environ Health 2020 Jul;46(4):446–53.

https://doi.

org/10.5271/sjweh.3885.

23. Akerstedt

Shift work and disturbed sleep/wakefulness.

Occup Med (Lond) 2003 Mar;53(2):89–94.

https://doi.

org/10.1093/occmed/kqg046.

24. Sallinen M, Kecklund G. Shift work, sleep, and sleepiness

- differences between shift schedules and systems. Scand J

Work Environ Health 2010 Mar;36(2):121–33.

https://doi.

org/10.5271/sjweh.2900.

25. Vanttola P, Puttonen

Karhula

Oksanen

Härmä M.

10.

Stevens

RG. Electric power use and breast cancer: a

hypothesis. Am J Epidemiol 1987 Apr;125(4):556–61.

https://doi.org/10.1093/oxfordjournals.aje.a114569.

11. Figueiro MG, Rea MS, Bullough JD. Circadian effectiveness

of two polychromatic lights in suppressing human nocturnal

melatonin.

Neurosci Lett

2006 Oct;406(3):293–7.

https://

doi.org/10.1016/j.neulet.2006.07.069.

12.

Thapan K,

Arendt J, Skene DJ. An action spectrum

for melatonin suppression: evidence for a novel non-

rod, non-cone photoreceptor system in humans. J

Physiol 2001 Aug;535(Pt 1):261–7.

https://doi.

org/10.1111/j.1469-7793.2001.t01-1-00261.x.

13. Rea MS, Figueiro MG. Quantifying light-dependent

Scand J Work Environ Health – online first

BEU, Alm.del - 2019-20 - Bilag 377: Orientering om NFA-artikel med forskningsbaserede anbefalinger om tilrettelæggelse af natarbejde, fra beskæftigelsesministeren

Garde et al

Prevalence of shift work disorder among hospital personnel:

A cross-sectional study using objective working hour data.

J Sleep Res. 2020; 29:e12906.

https://doi.org/10.1111/

jsr.12906.

26. Flo E, Pallesen

Magerøy

Moen BE, Grønli J,

Hilde Nordhus

et al. Shift work disorder in nurses--

assessment, prevalence and related health problems. PLoS

One 2012;7(4):e33981.

https://doi.org/10.1371/journal.

pone.0033981.

27. Cappuccio FP, Cooper D, D’Elia

Strazzullo P, Miller

MA. Sleep duration predicts cardiovascular outcomes:

a systematic review and meta-analysis of prospective

studies.

Eur Heart J 2011 Jun;32(12):1484–92.

https://doi.

org/10.1093/eurheartj/ehr007.

28. Vgontzas AN, Fernandez-Mendoza J,

Liao

D, Bixler EO.

Insomnia with objective short sleep duration: the most

biologically severe phenotype of the disorder. Sleep Med

Rev 2013 Aug;17(4):241–54.

https://doi.org/10.1016/j.

smrv.2012.09.005.

29. Blask DE. Melatonin, sleep disturbance and cancer risk.

Sleep Med Rev 2009 Aug;13(4):257–64.

https://doi.

org/10.1016/j.smrv.2008.07.007.

30. Williamson A, Lombardi DA, Folkard

S, Stutts

J, Courtney

TK,

Connor JL. The link between fatigue and safety.

Accid Anal Prev 2011 Mar;43(2):498–515.

https://doi.

org/10.1016/j.aap.2009.11.011.

31. Bjorvatn

Stangenes

Oyane

Forberg

Lowden

A, Holsten F et al. Subjective and objective measures of

adaptation and readaptation to night work on an oil rig in

the North Sea.

Sleep 2006 Jun;29(6):821–9.

https://doi.

org/10.1093/sleep/29.6.821.

32.

Behrens T,

Burek

Pallapies D,

Kösters L, Lehnert

Beine

A, et al. Decreased psychomotor vigilance of

female shift workers after working night shifts. PloS one.

2019;14(7):e0219087-e.

33. Ganesan

Magee M,

Stone

JE, Mulhall MD, Collins A,

Howard ME et al. The Impact of Shift Work on Sleep,

Alertness and Performance in Healthcare Workers. Sci Rep

2019 Mar;9(1):4635.

https://doi.org/10.1038/s41598-019-

40914-x.

34.

Lamond N,

Dorrian J, Burgess H, Holmes A, Roach G,

McCulloch

et al. Adaptation of performance during

a week of simulated night work. Ergonomics 2004

Feb;47(2):154–65.

https://doi.org/10.1080/0014013031000

1617930.

35. McHill AW, Wright KP Jr. Cognitive Impairments during

the Transition to Working at Night and on Subsequent Night

Shifts. J Biol Rhythms 2019 Aug;34(4):432–46.

https://doi.

org/10.1177/0748730419848552.

36. Mulhall MD, Sletten

TL,

Magee M,

Stone

JE, Ganesan

Collins A et al. Sleepiness and driving events in

shift workers: the impact of circadian and homeostatic

factors. Sleep (Basel) 2019 Jun;42(6):zsz074.

https://doi.

org/10.1093/sleep/zsz074.

37. Pylkkönen M, Sihvola M, Hyvärinen HK, Puttonen

Hublin C, Sallinen M. Sleepiness, sleep, and use of

sleepiness countermeasures in shift-working long-haul truck

drivers.

Accid Anal Prev 2015 Jul;80:201–10.

https://doi.

org/10.1016/j.aap.2015.03.031.

38.

Santhi N,

Horowitz

TS,

Duffy JF, Czeisler CA. Acute sleep

deprivation and circadian misalignment associated with

transition onto the first night of work impairs visual selective

attention.

PLoS One 2007 Nov;2(11):e1233.

https://doi.

org/10.1371/journal.pone.0001233.

39. Driscoll TR, Grunstein RR, Rogers

NL.

A systematic

review of the neurobehavioural and physiological effects of

shiftwork systems. Sleep Med Rev 2007 Jun;11(3):179–94.

https://doi.org/10.1016/j.smrv.2006.11.001.

40. Axelsson J, Kecklund G, Akerstedt

Lowden A. Effects

of alternating 8- and 12-hour shifts on sleep, sleepiness,

physical effort and performance. Scand J Work Environ

Health 1998;24 Suppl 3:62–8.

41. Rosa RR,

Bonnet

MH. Performance and alertness on

8 h and 12 h rotating shifts at a natural gas utility.

Ergonomics 1993 Oct;36(10):1177–93.

https://doi.

org/10.1080/00140139308967987.

42.

Stevens

RG, Hansen J, Costa G, Haus E,

Kauppinen T,

Aronson KJ et al. Considerations of circadian impact for

defining ‘shift work’ in cancer studies: IARC Working

Group Report. Occup Environ Med 2011 Feb;68(2):154–62.

https://doi.org/10.1136/oem.2009.053512.

43. Davis

Mirick DK,

Stevens

RG. Night shift work,

light at night, and risk of breast cancer. J Natl Cancer

Inst

2001 Oct;93(20):1557–62.

https://doi.org/10.1093/

jnci/93.20.1557.

44.

Vetter C, Dashti HS,

Lane

JM, Anderson SG,

Schernhammer

ES, Rutter MK et al. Night Shift Work, Genetic Risk, and

Type 2 Diabetes in the UK Biobank. Diabetes Care 2018

Apr;41(4):762–9.

https://doi.org/10.2337/dc17-1933.

45. Hansen J,

Lassen

CF. Nested case-control study of night

shift work and breast cancer risk among women in the

Danish military. Occup Environ Med 2012 Aug;69(8):551–

https://doi.org/10.1136/oemed-2011-100240.

46.

Cordina-Duverger E, Menegaux F, Popa A, Rabstein

Harth V, Pesch

et al. Night shift work and breast

cancer: a pooled analysis of population-based case-control

studies with complete work history. Eur J Epidemiol 2018

Apr;33(4):369–79.

https://doi.org/10.1007/s10654-018-

0368-x.

47.

Ferguson JM, Costello

Neophytou AM, Balmes JR,

Bradshaw PT, Cullen MR et al. Night and rotational

work exposure within the last 12 months and risk of

incident hypertension. Scand J Work Environ Health 2019

May;45(3):256–66.

https://doi.org/10.5271/sjweh.3788.

48.

Nielsen HB,

Larsen

AD, Dyreborg J, Hansen AM, Pompeii

LA, Conway SH et al. Risk of injury after evening and night

work - findings from the Danish Working Hour Database.

Scand J Work Environ Health 2018 Jul;44(4):385–93.

https://doi.org/10.5271/sjweh.3737.

49.

Lie

JA, Kjuus H, Zienolddiny

Haugen A,

Stevens

RG,

Scand J Work Environ Health – online first

BEU, Alm.del - 2019-20 - Bilag 377: Orientering om NFA-artikel med forskningsbaserede anbefalinger om tilrettelæggelse af natarbejde, fra beskæftigelsesministeren

Night shift schedules and health and safety risks

Kjærheim

Night work and breast cancer risk among

Norwegian nurses: assessment by different exposure

metrics.

Am J Epidemiol 2011 Jun;173(11):1272–9.

https://

doi.org/10.1093/aje/kwr014.

50. Wendeu-Foyet MG, Bayon V, Cénée

Trétarre

Rébillard

Cancel-Tassin G et al. Night work and prostate cancer

risk: results from the EPICAP Study. Occup Environ

Med 2018 Aug;75(8):573–81.

https://doi.org/10.1136/

oemed-2018-105009.

51. Fischer D, Lombardi DA, Folkard

Willetts J, Christiani

DC. Updating the “Risk Index”: A systematic review and

meta-analysis of occupational injuries and work schedule

characteristics.

Chronobiol Int 2017;34(10):1423–38.

https://doi.org/10.1080/07420528.2017.1367305.

52. Härmä M, Koskinen A, Sallinen M, Kubo

Ropponen A,

Lombardi DA. Characteristics of working hours and the risk

of occupational injuries among hospital employees: a case-

crossover study. Scand J Work Environ Health – online first.

https://doi.org/10.5271/sjweh.3905.

[Epub ahead of print].

53. Waage

Harris A, Pallesen

Saksvik

IB,

Moen BE,

Bjorvatn

Subjective and objective sleepiness among oil

rig workers during three different shift schedules. Sleep

Med 2012 Jan;13(1):64–72.

https://doi.org/10.1016/j.

sleep.2011.04.009.

54. Bjorvatn

Stangenes

Oyane

Forberg

Lowden

A, Holsten F et al. Subjective and objective measures of

adaptation and readaptation to night work on an oil rig in

the North Sea.

Sleep 2006 Jun;29(6):821–9.

https://doi.

org/10.1093/sleep/29.6.821.

55. Forberg

Waage

Moen

Bjorvatn

Subjective

and objective sleep and sleepiness among tunnel workers

in an extreme and isolated environment: 10-h shifts,

21-day working period, at 78 degrees north. Sleep

Med 2010 Feb;11(2):185–90.

https://doi.org/10.1016/j.

sleep.2009.07.015.

56. Harris A, Waage

Ursin H, Hansen AM, Bjorvatn

Eriksen HR. Cortisol, reaction time test and health

among offshore shift workers. Psychoneuroendocrinology

2010 Oct;35(9):1339–47.

https://doi.org/10.1016/j.

psyneuen.2010.03.006.

57. Folkard

Do permanent night workers show circadian

adjustment? A review based on the endogenous melatonin

rhythm. Chronobiol Int 2008 Apr;25(2):215–24.

https://doi.

org/10.1080/07420520802106835.

58. Hansen J,

Stevens

RG. Case-control study of shift-work

and breast cancer risk in Danish nurses: impact of shift

systems. Eur J Cancer 2012 Jul;48(11):1722–9.

https://doi.

org/10.1016/j.ejca.2011.07.005.

59. Papantoniou

Castaño-Vinyals G, Espinosa A, Aragonés

Pérez-Gómez

Burgos J et al. Night shift work,

chronotype and prostate cancer risk in the MCC-Spain

case-control study. Int J Cancer 2015 Sep;137(5):1147–57.

https://doi.org/10.1002/ijc.29400.

60. Papantoniou

Castaño-Vinyals G, Espinosa A, Aragonés

Pérez-Gómez

Ardanaz E et al. Breast cancer risk

and night shift work in a case-control study in a Spanish

population. Eur J Epidemiol 2016 Sep;31(9):867–78.

https://

doi.org/10.1007/s10654-015-0073-y.

61. Nielsen HB, Hansen AM, Conway SH, Dyreborg J, Hansen

J, Kolstad HA et al. Short time between shifts and risk

of injury among Danish hospital workers: a register-

based cohort study. Scand J Work Environ Health 2019

Mar;45(2):166–73.

https://doi.org/10.5271/sjweh.3770.

62. Vedaa

Ø,

Harris A, Waage

Bjorvatn

B, Thun

E, Buchvold

HV et al. A longitudinal study on the association between

quick returns and occupational accidents. Scand J Work

Environ Health - online first.

https://doi.org/10.5271/

sjweh.3906.

63. Bambra CL, Whitehead MM, Sowden AJ, Akers J, Petticrew

MP. Shifting schedules: the health effects of reorganizing

shift work. Am J Prev Med 2008 May;34(5):427–34.

https://

doi.org/10.1016/j.amepre.2007.12.023.

64.

Orth-Gomér

Intervention on coronary risk factors by

adapting a shift work schedule to biologic rhythmicity.

Psychosom Med 1983 Oct;45(5):407–15.

https://doi.

org/10.1097/00006842-198310000-00004.

65.

Barton

J, Folkard

Advancing versus delaying shift

systems. Ergonomics 1993 Jan-Mar;36(1-3):59–64.

https://

doi.org/10.1080/00140139308967855.

66.

Kubo

Oyama

Nakamura

T, Kunimoto

M, Kadowaki

Otomo H, et al. Industry-based retrospective cohort study of

the risk of prostate cancer among rotating-shift workers. Int J

Urology. 2011 Mar;18(3):206–11.

https://doi.org/10.1111/

j.1442-2042.2010.02714.x.

67.

Nakamura Y,

Tamura

Kashida S,

Takayama H, Yamagata

Y, Karube A et al. Changes of serum melatonin level and its

relationship to feto-placental unit during pregnancy. J Pineal

Res 2001 Jan;30(1):29–33.

https://doi.org/10.1034/j.1600-

079X.2001.300104.x.

68.

Reiter RJ,

Tan

DX, Korkmaz A, Rosales-Corral SA.

Melatonin and stable circadian rhythms optimize maternal,

placental and fetal physiology. Hum Reprod Update 2014

Mar-Apr;20(2):293–307.

https://doi.org/10.1093/humupd/

dmt054.

69.

Tamura

H, Takasaki A, Taketani

Tanabe M,

Lee L,

Tamura I

et al. Melatonin and female reproduction. J Obstet

Gynaecol Res 2014 Jan;40(1):1–11.

https://doi.org/10.1111/

jog.12177.

70. Palmer

KT,

Bonzini M, Harris EC, Linaker C,

Bonde

JP.

Work activities and risk of prematurity, low birth weight

and pre-eclampsia: an updated review with meta-analysis.

Occup Environ Med 2013 Apr;70(4):213–22.

https://doi.

org/10.1136/oemed-2012-101032.

71.

Bonde

JP, Jørgensen

KT,

Bonzini M, Palmer

KT.

Miscarriage and occupational activity: a systematic

review and meta-analysis regarding shift work, working

hours, lifting, standing, and physical workload. Scand J

Work Environ Health 2013 Jul;39(4):325–34.

https://doi.

org/10.5271/sjweh.3337.

72. Begtrup LM,

Specht

IO, Hammer PE, Flachs EM, Garde

Scand J Work Environ Health – online first

BEU, Alm.del - 2019-20 - Bilag 377: Orientering om NFA-artikel med forskningsbaserede anbefalinger om tilrettelæggelse af natarbejde, fra beskæftigelsesministeren

Garde et al

AH, Hansen J et al. Night work and miscarriage: a Danish

nationwide register-based cohort study. Occup Environ

Med 2019 May;76(5):302–8.

https://doi.org/10.1136/

oemed-2018-105592.

73. Hammer PE, Garde AH, Begtrup LM, Flachs EM, Hansen

J, Hansen AM et al. Night work and sick leave during

pregnancy: a national register-based within-worker cohort

study. Occup Environ Med 2019 Mar;76(3):163–8.

https://

doi.org/10.1136/oemed-2018-105331.

74.

Hammer P, Flachs E,

Specht I,

Pinborg A, Petersen

Larsen

A et al. Night work and hypertensive disorders of

pregnancy: a national register-based cohort study.

Scand

J Work Environ Health 2018 Jul;44(4):403–13.

https://doi.

org/10.5271/sjweh.3728.

75. Fischer D, Lombardi DA, Marucci-Wellman H, Roenneberg

Chronotypes in the US - Influence of age and sex. PLoS

One 2017 Jun;12(6):e0178782.

https://doi.org/10.1371/

journal.pone.0178782.

76.

Van Cauter E, Plat

Leproult R, Copinschi G. Alterations

of circadian rhythmicity and sleep in aging: endocrine

consequences. Horm Res 1998;49(3-4):147–52.

77.

Pallesen

S, Nordhus

IH, Omvik

S, Sivertsen B,

Tell GS,

Bjorvatn

Prevalence and risk factors of subjective

sleepiness in the general adult population. Sleep 2007

May;30(5):619–24.

https://doi.org/10.1093/sleep/30.5.619.

78.

Härmä M, Sallinen M, Ranta R, Mutanen P, Müller

K. The

effect of an irregular shift system on sleepiness at work in

train drivers and railway traffic controllers. J Sleep Res

2002 Jun;11(2):141–51.

https://doi.org/10.1046/j.1365-

2869.2002.00294.x.

79. Härmä MI, Hakola

Åkerstedt

T, Laitinen

JT. Age and

adjustment to night work. Occup Environ Med 1994

Aug;51(8):568–73.

https://doi.org/10.1136/oem.51.8.568.

80. Härmä M, Karhula

Ropponen A, Puttonen

Koskinen A,

Ojajärvi A et al. Association of changes in work shifts and

shift intensity with change in fatigue and disturbed sleep: a

within-subject study. Scand J Work Environ Health 2018

Jul;44(4):394–402.

https://doi.org/10.5271/sjweh.3730

81. Härmä M, Gustavsson P, Kolstad HA. Shift work and

cardiovascular disease - do the new studies add to

our knowledge? Scand J Work Environ Health 2018

May;44(3):225–8.

https://doi.org/10.5271/sjweh.3727.

82. Wong

IS,

Dawson D, VAN Dongen HP. International

consensus statements on non-standard working time

arrangements and occupational health and safety.

Ind Health 2019;57(2):135–8.

https://doi.org/10.2486/

indhealth.57_202.

83. Lowden A, Öztürk G, Reynolds A, Bjorvatn

Working

Time Society consensus statements: evidence based

interventions using light to improve circadian adaptation to

working hours. Ind Health 2019 Apr;57(2):213–27.

https://

doi.org/10.2486/indhealth.SW-9.

84.

Nabe-Nielsen

Kecklund G, Ingre M, Skotte J,

Diderichsen F, Garde AH. The importance of individual

preferences when evaluating the associations between

working hours and indicators of health and well-being. Appl

Ergon 2010 Oct;41(6):779–86.

https://doi.org/10.1016/j.

apergo.2010.01.004.

85. Nijp HH, Beckers DG, Geurts SA, Tucker P,

Kompier

MA. Systematic review on the association between

employee worktime control and work-non-work balance,

health and well-being, and job-related outcomes. Scand J

Work Environ Health 2012 Jul;38(4):299–313.

https://doi.

org/10.5271/sjweh.3307.

86.

Pallesen

Bjorvatn

Magerøy

Saksvik

IB,

Waage

Moen BEJ. Measures to counteract the negative effects

of night work. Scand J Work Environ Health 2010

Mar;36(2):109–20.

https://doi.org/10.5271/sjweh.2886.

87.

Arlinghaus A, Bohle P, Iskra-Golec

Jansen

Jay

Rotenberg

Working Time Society consensus statements:

evidence-based effects of shift work and non-standard

working hours on workers, family and community.

Ind

Health 2019 Apr;57(2):184–200.

https://doi.org/10.2486/

indhealth.SW-4.

88.

Jones ME, Schoemaker MJ, McFadden EC, Wright

LB,

Johns LE, Swerdlow AJ. Night shift work and risk of breast

cancer in women: the Generations Study cohort. Br J Cancer

2019 Jul;121(2):172–9.

https://doi.org/10.1038/s41416-019-

0485-7.

89.

Specht

IO, Hammer PE, Flachs EM, Begtrup LM,

Larsen

AD, Hougaard

et al. Night work during pregnancy and

preterm birth-A large register-based cohort study. PLoS One

2019 Apr;14(4):e0215748.

https://doi.org/10.1371/journal.

pone.0215748.

Received for publication: 4 May 2020

Scand J Work Environ Health – online first