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Night shift work increases the risk for type 2 diabetes

Authors:
John Axelsson at Stockholm University
John Axelsson
Sampsa Puttonen at Tampere University
Sampsa Puttonen
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Aetiology
1
Evidence-Based Medicine XXX 2012 | volume 00 | number 00 |
10.1136/ebmed-2012-100649
1Clinical Neuroscience, Division
of Psychology, Karolinska
Institute, Stockholm, Sweden
2Finnish Institute of Occupational
Health, Helsinki, Finland
Correspondence to
John Axelsson
Karolinska Institute,
Department. of Clinical
Neuroscience, Division of
Psychology, 17177 Stockholm,
Sweden; john.axelsson@ki.se
Study
Night shift work increases the risk for type 2 diabetes
John Axelsson,1 Sampsa Puttonen2
Context
As a result of the rapidly evolving 24-h society, about
15–30% of the workforce works outside normal business
hours, with about half of them working night shifts. Any
shift worker knows that night work compromises cogni-
tive capacity and challenges the physiological need for
sleep and recuperation. It is not surprising therefore that
night shift work relates to a variety of health problems,
including sleep disturbances, gastro-intestinal disorders,
cancer and a number of metabolic disorders such as obe-
sity, the metabolic syndrome, cardiovascular disease and
type 2 diabetes.1 However, many previous studies have
not fully captured the relationship between these health
problems and shift work exposure.
Methods
Over 177 000 women from two large prospective cohort
studies (Nurses’ Health Study I and II) covering ages
25–67 years were followed up for 20 years. They rated
whether they had worked at least 3 night shifts per month
in addition to days and evenings in that month. They
were re-surveyed at 2–4 year intervals. The effect of
shift work on the self-reported incidence type 2 diabetes,
measured 18–20 years later, was tested using Cox pro-
portional hazards regression models with adjustment for
relevant confounders.
Findings
Both cohorts showed a gradual increase in type 2 diabetes
risk with increased exposure to shift work. Compared with
day workers, the pooled HRs for having worked 1–2, 3–9,
10–19, ≥20 years of shift work were 1.05, 1.20, 1.40 and
1.58, respectively. Exposure to shift work was also related
to weight gain, and adjustments for body mass reduced
the associations with diabetes risk by about 50%.
Commentary
The study by Pan et al demonstrates a clear association
between shift work and type 2 diabetes. This is in line
with previous studies reporting an association between
shift work and several metabolic disorders, including
type 2 diabetes.1 Strengths of the study include a large
sample size, long follow-up period and good-quality
data on shift work exposure. Type 2 diabetes status was
self-reported and was further con rmed with supple-
mentary questionnaires. Type 2 diabetes can probably be
reliably measured with self-reports in nurses, even if it
may be insuf cient in other groups. Importantly, this
Commentary on: Pan A, Schernhammer ES, Sun Q, et al. Rotating night shift work and risk of type 2
diabetes: two prospective cohort studies in women. PLoS Med 2011;8:e1001141.
study supports that shift work is also a metabolic risk
factor for younger workers, and not just a problem with
increasing age. Correspondingly, young shift work-
ers also have an increased risk to develop subclinical
atherosclerosis.2
The results con rm and extend the  ndings of a
Swedish study reporting an increased risk for diabetes-
related mortality with exposure to shift work.3 Potential
methodological problems of both these studies con-
cern how to properly analyse exposure and the ‘healthy
worker effect’. Self-ratings of exposure to shift work may
not be fully reliable since it is dif cult to adequately sum
up whether one has worked three nights in a month in a
varying shift schedule. An example of the ‘healthy worker
effect’ is that shift workers with a high risk of develop-
ing diabetes are twice as likely to leave their working
organisations.4 Thus, the risks of exposure to night shift
work are probably underestimated. To sum up, the results
showed that working ≥3 night shifts per month increases
the risk of type 2 diabetes. In order to generate guidelines
for exposure and ergonomic shift schedules, additional
knowledge is needed on how many nights a person can
work safely in a month.
Several strategies can reduce health risks among
shift workers. First, organisations should acknowledge
that shift work is a metabolic risk factor and actively use
strategies to improve life-style. Second, health screen-
ing for individuals who may be vulnerable to shift
work or its health effects could be conducted dur-
ing recruitment of employees.5 Third, regular health
check-ups are needed in young shift workers. Even a
simple screening questionnaire can ef ciently detect the
risk for metabolic disorders.6 Fourth, use of ergonomic
working schedules and individual solutions should be
adopted more widely. For example, changing to a more
ergonomic schedule improves blood lipids and blood
pressure. Lastly, shift-workers need to be educated to
cope better with shift-work (eating, sleeping and exercis-
ing) and the use of countermeasures (eg, naps) should be
widened.
Competing interests None.
References
1. Puttonen S, Härmä M, Hublin C. Shift work and cardiovascular
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2. Puttonen S, Kivimäki M, Elovainio M, et al. Shift work in
young adults and carotid artery intima-media thickness:
The Cardiovascular Risk in Young Finns study. Atherosclerosis
2009;205:608–13.
ebmed-2012-100649.indd 1ebmed-2012-100649.indd 1 5/16/2012 11:44:59 AM5/16/2012 11:44:59 AM
Aetiology
2Evidence-Based Medicine XXX 2012 | volume 00 | number 00 |
3. Karlsson B, Alfredsson L, Knutsson A, et al. Total mortality and
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care identi es risk for type 2 diabetes and cardiovascular
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ebmed-2012-100649.indd 2ebmed-2012-100649.indd 2 5/16/2012 11:44:59 AM5/16/2012 11:44:59 AM
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Measures to counteract the negative effects of night work
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  • Dec 2009
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Night work is associated with several negative health outcomes as well as accidents and reduced productivity. The aim of this study was to identify factors that may counteract the negative effects of night work. We conducted searches for studies of scientifically based countermeasures of the negative effects of night work in PubMed and Thomson Reuters' ISI Web of Knowledge and inspected the reference lists of relevant literature. We identified studies describing countermeasures such as proper personnel selection, bright light therapy, melatonin administration, naps, exercise, sleepiness detection devices, and the use of stimulants to improve wakefulness and hypnotics to improve daytime sleep. There is some research supporting countermeasures (eg, bright light, melatonin, naps, use of stimulants, proper work scheduling) as a means to improve adaptation to night work. However, there is little evidence that such countermeasures reduce the long-term health consequences of night work. Future studies should aim at identifying both work and individual factors which are related to differential health outcomes of night work. Better study designs (eg, longitudinal designs and use of standardized outcome measures) are needed in future research.
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Shift work in young adults and carotid artery intima-media thickness: The Cardiovascular Risk in Young Finns study
Article
Full-text available
  • Feb 2009
Shift work is associated with an elevated risk of cardiovascular disease, but the timing or mechanisms of this association is unclear. We examined the relationship between shift work and subclinical atherosclerosis in 1543 (712 men and 831 women, 24-39 years old) young adults as part of the ongoing population-based Cardiovascular Risk in Young Finns study. Carotid atherosclerosis was assessed by measuring the thickness of the common carotid artery intima-media (IMT) complex with ultrasound and carotid plaque. Working schedules were categorized as day work or shift work (2- or 3-shift work, regular evening or night work). In men, shift work was associated with higher mean IMT (B=0.029, p=0.021), maximum IMT (B=0.029, p=0.028), and a 2.2-fold odds of carotid plaque (95% CI, 1.2-4.0). These relationships persisted after adjustment for age and risk factors, such as low socio-economic position, job strain, smoking, diet, family history of CHD, physical inactivity, alcohol consumption, obesity, homocysteine, C-reactive protein, blood pressure, and lipids. In women, no association was found between shift work and carotid atherosclerosis indicators. Our results suggest that shift work accelerates the atherosclerotic process and that the effects of shift work on subclinical atherosclerosis are observable in men already before age 40.
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Total mortality and cause-specific mortality of Swedish shift- and dayworkers in the pulp and paper industry in 1952-2001
Article
Full-text available
  • Mar 2005
The study investigated the relationship between shiftwork and mortality, both total mortality and cause-specific mortality from coronary heart disease (CHD), stroke, and diabetes. Methods The cohort consisted of 2354 shiftworkers and 3088 dayworkers in two pulp and paper manufacturing plants. The mortality of the cohort was monitored from 1 January 1952 to 31 December 2001 by linkage to the national Cause of Death Register. Groups of workers defined by different durations of shiftwork exposure were compared with dayworkers by calculating standardized relative rates (SRR). Death due to any cause (total mortality) was not higher among the shiftworkers than among the dayworkers [SRR 1.02, 95% confidence interval (95% CI) 0.93-1.11]. A longer duration of shiftwork was associated with an increased risk of CHD, and shiftworkers with >30 years of shiftwork had the highest risk of CHD (SRR 1.24, 95% CI 1.04-1.49) Diabetes was more common as the number of shift years of exposure increased [b(linear coefficient) = 4.14 x 10(-5), 95% CI 2.46 x 10(-5) -5.81 x 10(-5)]. Compared with dayworkers, shiftworkers had a greater risk of death due to stroke (SRR 1.56, 95% CI 0.98-2.51). In the present study, no general increase in mortality was observed among shiftworkers when they were compared with dayworkers. However, the results demonstrate an increased mortality from CHD among shiftworkers with a long duration of shiftwork exposure. Mortality due to diabetes also increased as the number of shift years and mortality due to ischemic stroke in shiftworkers increased.
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Prevalent cardiovascular disease, risk factors and selection out of shift work
Article
Full-text available
  • Jul 2006
This study examines whether health-related selection out of shift work is likely to bias the association between shift work and cardiovascular disease (CVD). Survey data on doctor-diagnosed CVD (myocardial infarction, angina, or hypertension) and risk factors (high blood pressure, high cholesterol concentration, obesity, and diabetes) were collected in 2000-2002 for a cohort of 7037 female nurses (5038 shift workers, 1999 day workers) in 21 Finnish hospitals. The follow-up in 2004 determined those who had left their workplace or changed from shift work to day work. Among the shift workers, the age-adjusted odds for leaving the organization was 1.83 (95% CI 1.01-3.32) times higher for those with prevalent diabetes and 2.21 (95% CI 1.12-4.39) times higher for those with three to four risk factors than for their counterparts with no diabetes or risk factors. The associations between CVD risk factors and leaving the organization were similar for the day workers. The prevalent CVD and risk factors did not predict a change to day work among the shift workers who remained in the organization during the entire follow-up period. Employees with several risk factors are more likely to leave an organization regardless of the type of work schedule. Health-related selection out of shift work is an unlikely source of major bias in research on shift work and CVD.
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Occupational health care identifi es risk for type 2 diabetes and cardiovascular disease. Prim Care Diabetes
  • Feb 2012
  • K Viitasalo
  • J Lindström
  • K Hemiö
Viitasalo K, Lindström J, Hemiö K, et al. Occupational health care identifi es risk for type 2 diabetes and cardiovascular disease. Prim Care Diabetes. Published Online First 3 February 2012. doi:10.1016/j.pcd.2012.01.003