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Study links shift work to increased risk of diabetes

Fri, 2014-07-25 04:40

“Type 2 diabetes is more common in people who work shifts, a large international study suggests,” BBC News reports.

The BBC reports on a review that searched the literature and found 12 studies including more than 225,000 people which looked at the link between shift work and diabetes.

When pooling the results the researchers found that overall, shift work was associated with a 9% increased risk of diabetes. The association was found to be stronger in men (37%) and for those working rotating shifts – such as two weeks on nights, two weeks on days (42%).

However, there are problems with concluding from these studies that there really is a link between shift work and developing diabetes. For example, it is difficult to establish cause and effect, because it’s not completely clear that people hadn’t already got diabetes at the time their shift work pattern was being assessed. It’s further unclear whether the apparent relationship may not just be caused because of other factors that are associated with both shift work and diabetes (such as diet and activity).

Also, none of the 12 studies were conducted in the UK, and half were from Japan. While the results may be applicable here, different cultures may have different a work ethic, environmental and health differences, meaning that they cannot so easily be generalised to all populations.

The identified relationship is undoubtedly worthy of further study, to see whether shift work could have direct biological effects on the body that lead to the development of diabetes.

 

Where did the story come from?

The study was carried out by researchers from Huazhong University of Science and Technology, Wuhan, Hubei, and Jiangxi Science and Technology Normal University, Nanchang, Jiangxi, both in China.

No sources of financial support are reported and the authors declare no conflicts of interest.

The study was published in the peer-reviewed journal of Occupational and Environmental Medicine. 

The UK media accurately reports the results of this study, and discusses the possible causes and hazards of shift working, such as disruption to the “body clock”, which seem plausible, if unproven. However, they do not highlight the study's limitations.

 

What kind of research was this?

This was a systematic review and meta-analysis.

Researchers searched the literature from across the world to find observational studies that have examined whether shift work may be associated with the risk of type 2 diabetes. The researchers then pooled the results of these studies.

Type 2 diabetes is a global health problem, and it is estimated that in just over 10 years time the number of cases could have increased by 65% to reach 380 million cases worldwide.

Diabetes is associated with considerable ill health and mortality. So identifying modifiable risk factors that may reduce risk of the disease developing is highly important. Being overweight or obese is the most well established modifiable risk factor for type 2 diabetes.

The researchers say that shift work, with its irregular working hours and rotating schedule has been demonstrated to have some effect on sleep patterns, tiredness, cognitive capacity, and digestion.

Some studies have even linked it with breast cancer and vascular disease. Therefore, this review aimed to look at the possible association with diabetes.

 

What did the research involve?

The researchers searched several literature bases for studies published up to April 2014 that have examined an association between shift work and diabetes, using relevant search terms, including impaired glucose tolerance and insulin resistance. Any study design or study population was eligible, but only studies in the English language were included. The researchers pooled observational studies that had directly examined the link between shift work as an exposure and diabetes as an outcome.

Shift work schedules were categorised as rotating, irregular and unspecified, night, mixed and evening.

Studies examining non-work-related nighttime activities/light exposure were excluded. Two researchers extracted data and assessed the quality of the studies.

 

What were the basic results?

Twelve studies met inclusion criteria: eight cohort studies (seven prospective, one retrospective), and four cross sectional studies, published between 1983 and 2013. The 12 studies included a total 226,652 people, with sample size in individual studies ranging between 475 and 107,915. There were a total 14,595 people with diabetes (6% of the total sample). Six studies came from Japan, two from the US, two from Sweden, one from Belgium and one from China. Eight of the studies included only men, two both sexes, and two women only.

The pooled results of all studies found that shift work was associated with a 9% increased risk of diabetes (odds ratio (OR) 1.09, 95% confidence interval (CI) 1.05 to 1.12).

The odds ratios when pooling only cohort studies and only cross sectional studies were fairly similar (slightly higher odds for cohort studies of 12% versus 6% for cross sectional).

They then carried out further sub-analyses to examine whether specific factors were associated. The odds of diabetes were much higher for men (37% increased risk) than for women (9%).

There was a significant association with diabetes for rotating shifts, irregular or unspecific shifts and night shifts; but no link for mixed or evening shifts. The largest association with diabetes was for rotating shifts (42% risk).

Sub-analyses of studies that had controlled for body mass index (BMI) in their models, and of studies that had controlled for physical activity in their models still found similar, significant links (7% increased odds of diabetes).

 

How did the researchers interpret the results?

The researchers conclude that “shift work is associated with an increased risk of diabetes. The increase was significantly higher among men and the rotating shift group, which warrants further studies”.

 

Conclusion

This systematic review finds an association between shift work and diabetes, overall the pooled results found that shift work was associated with a 9% risk of diabetes. The review has strengths in that it has reviewed the global literature and identified a reasonable sample of 12 observational studies including more than 225,000 people.

However, there are various important limitations that need to be taken into account before concluding that shift work directly increases the risk of diabetes.

Type 1 or type 2?

The main point under investigation was whether shift work could be a modifiable risk factor for the development of type 2 diabetes – the condition where people either produce less insulin, or their body is less sensitive to the effect of insulin – rather than the autoimmune condition of type 1 diabetes, which is not caused by lifestyle. However, all of the review’s results and reports of the individual studies just discuss “diabetes”. It is likely that most of these studies would have been looking at how shift work was associated with type 2 diabetes, but this is not clear.

Lack of clarity on diagnosis

It is not clear from the review whether these studies had definitely included a population of people who were all free from type 2 diabetes at the start, assessed their shift working pattern, and then looked at whether they developed type 2 diabetes during follow-up.

All we know is that the studies have looked at the association between shift work and diabetes. We don’t know whether all studies excluded diabetes at the start, and then used valid criteria to diagnose diabetes during follow-up.

If people already had diabetes (diagnosed or undiagnosed) at the time their shift working pattern was being assessed, then this doesn’t tell us anything about cause and effect. Given that four of the studies were cross sectional anyway, meaning that they are just snapshots in time, the fact that people have diabetes and are currently shift working doesn’t necessarily mean that shift working has caused the diabetes. 

Confounders

Because all the studies were observational (some cross-sectional), we cannot exclude the possibility that any association between diabetes and shift work is being influenced by confounding.

The review conducted sub-analyses only of studies that controlled for BMI in their models, and those that controlled for physical activity (though none seem to have controlled for both).

But aside from family history, no other mention of confounding factors is given, and it is unclear how well studies may have controlled for other factors.

Various sociodemographic, health and lifestyle factors may be associated with both doing shift work, and with risk of diabetes. This could therefore mean that it is not shift work that directly causes diabetes, but the various factors that are associated with shift work that cause diabetes.

Limited study population

No included studies came from the UK, with half coming from Japan. Though it may well be the case that the results from all of these studies can be applied to the UK, different cultures may have different work ethic, environmental and health differences meaning that they cannot so easily be generalised to all populations.

Also, the majority of studies, eight of the 12, included male only populations, therefore the results may have more applicability to men doing shift work than women.

No information given on occupations

Finally, we do not know whether any association between shift work and diabetes may be influenced by the type of work that people are actually doing (routine or professional). 

The identified relationship is undoubtedly worthy of further study to see whether shift work could have direct biological effects on the body that lead to the development of diabetes. As we are increasingly a 24/7 economy, many people are expected to work unsociable shifts, and the health effects of shift work may become more noticeable.

If there is a link between shift work and diabetes (or other chronic diseases), it is equally possible at this stage that it could still be due to confounding from various sociodemographic, health and lifestyle factors that are associated with both shift work and risk of diabetes.

Overall, it cannot be firmly concluded at this stage whether and how shift work may be associated with diabetes.

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Links To The Headlines

Shift workers 'face type 2 diabetes risk'. BBC News, July 25 2014

Shift workers at higher risk of diabetes, study finds. The Guardian, July 25 2014

Shift workers more likely to develop diabetes, claims new research. The Independent, July 25 2014

Shift workers at higher risks of Type 2 diabetes: Chance of developing condition are biggest for men on rotating patterns. Daily Mail, July 25 2014

Shift workers run 'higher diabetes risk'. ITV News, July 25 2014

Links To Science

Gan Y, Yang C, Tong X, et al. Shift work and diabetes mellitus: a meta-analysis of observational studies. Occupational and Environmental Medicine. Published online July 16 2014

Categories: News

TV and gaming after work 'leads to feelings of guilt'

Fri, 2014-07-25 04:30

“Watching TV after work makes you feel ‘guilty and like a failure’,” says The Independent, citing a study looking at the concept of “ego depletion”.

Ego depletion is the idea that after a gruelling task your levels of self-control become drained. So after a hard day’s work, instead of going to the gym as you promised yourself, you spend the evening playing “Plants Vs Zombies” or watching repeats of “Mrs Brown’s Boys”.

Researchers felt that these procrastinations would cause feelings of guilt and shame. To test this hypothesis, they recruited 471 participants to take part in an online survey, either via a popular German gaming website, or directly through universities.

The survey involved asking people to say how strongly they agreed with 64 different heavily biased statements such as: “When I [watched TV/played video games] yesterday after work/school, I felt remorse.”

Unsurprisingly, the study reported that people used TV or video games to avoid doing other activities felt guilty about it. However, it is highly likely that this was due to the nature of these leading questions.

The study was also self-selecting, so results are not applicable to other populations who may use TV or games to relax.

A moderate amount of TV and gaming is unlikely to cause any serious problems as long as you balance it out with other real-world activities. Read more about how staying active can improve mental wellbeing.

 

Where did the story come from?

The study was carried out by researchers from Johannes Gutenberg University of Mainz in Germany and VU University Amsterdam. Sources of funding were not reported.

The study was published in the peer-reviewed Journal of Communication. It was published on an open-access basis so is free to read online.

The UK media have not discussed any of the limitations of this study but have simply focused on repeating the results without any critical analysis. They have also falsely implied that this study was able to confirm that watching TV or using video games causes feelings of guilt, when this type of study is not able to prove cause and effect.

It could have actually been the suggestive nature of the questions in the survey that made people report feeling guilty about their use of the media. The fact that the survey was self-selecting was also not discussed. University students and German-speaking fans of a video game website unlikely to be representative of the wider population.

 

What kind of research was this?

This was a cross-sectional study looking at TV and video game use, feelings of guilt, enjoyment and relaxation after working or studying during the day. This was performed using an online survey.

As this was a cross-sectional study, it takes place at one moment in time and thus cannot prove cause and effect, it can only show associations.

The researchers wanted to investigate the theory that people do not benefit from watching TV if they are “ego depleted”. This describes the emotional state a person is in after they have exhausted their willpower.

The researchers say this can occur after work from excessive self-regulation “found in making decisions, adjusting to social norms, avoiding mistakes”, and other tasks. 

Previous research has found that the likelihood of giving in to fleeting desires increased with the number of acts of self-control that had been done during the day. One example given was from a study that found that people were more likely to choose chocolate than a fruit salad as a snack if they had previously been given a series of puzzles to do.

The researchers proposed that use of media is one such desire used as a pleasurable task to put off doing more meaningful activities that demand more input and effort.

However, this could be interpreted by individuals as a sign of failed self-control and induce feelings of guilt and shame; lessening the experience of media use being a pleasurable experience.

The researchers aimed to assess the potential association between feeling “ego depleted” and negatively viewing their use of the media, and then the effects of this media use and perception of it on ego recovery (from the stress and strain of the day) and ability to enjoy the experience. They chose two different types of media – interactive (video games) and non-interactive (TV) to test their theories.

For TV, they also looked at whether the choice of programme made any difference.

 

What did the research involve?

The researchers recruited 293 people from an online gaming site and 342 students of psychology and communication (279 from a university in Germany and 63 from a university in Switzerland).

People were then excluded from the analyses who had not worked or studied the day before the survey and who had not played video games or watched TV.

The researchers say that in order to keep the questionnaire short, people who had used both types of media were assigned to only ask questions about their use of video games or TV use:

  • people who had been recruited from the gaming site and had used both media types were automatically assigned to questions about video game use
  • students who used both were assigned to answering questions about their TV use

The participants were asked to fill out the following online questionnaires:

  • State Self-Control Capacity Scale – 16 items to assess “ego depletion”, with responses from 1 (does not apply) to 7 (fully applies) for statements like “yesterday after work/school, I felt like my willpower was gone”
  • Procrastination Scale – 5 items to assess the level of stalling or putting off other activities
  • State Shame and Guilt Scale – 5 items, responding to statements such as “When I [watched TV/played video games] yesterday after work/school, I felt remorse”
  • Recovery Experience Questionnaire – 16 items on recovery such as becoming relaxed
  • Activation Deactivation Adjective Checklist – 10 items to assess levels of vitality, such as feeling energetic or sleepy after media use
  • Enjoyment – 3 items
  • Preference for challenging versus easy to watch TV – assessed using 9 items

They analysed the results to see if there was any evidence for their theory of an association between ego depletion, guilt about TV or video game use and lack of ego recovery in the form of relaxation.

 

What were the basic results?

Of the 653 respondents, 471 were eligible for the study and 61.8% of which were male. On average they had worked or studied for 6.5 hours the previous day, but this varied from half an hour to 16 hours.

Video game use was reported on by 262 people, who used it for an average of 2.6 hours (standard deviation (SD) 1.73). TV use was reported on by 209 people, and this was watched for on average 1.99 hours (SD 1.09).

The main results were:

  • video game and TV use were associated with putting off other activities
  • putting off other activities by using video games or TV was associated with feelings of guilt
  • guilt was associated with a negative effect on the ability of the media to induce ego recovery
  • guilt was associated with a negative effect on vitality
  • guilt was associated with a negative effect on the ability to enjoy the media
  • there was no difference in the results comparing use of video games or TV
  • people who were ego depleted were less likely to watch challenging TV content compared to easy TV content

 

How did the researchers interpret the results?

They conclude that their “results suggest that ego depletion is associated with similar patterns of negative appraisal and reduced positive outcomes in terms of wellbeing and enjoyment both in the context of interactive as well as non-interactive media use”.

 

Conclusion

This cross-sectional study reported an association between use of video games or TV after working and feelings of guilt about doing so, which hampered the ability to enjoy it or recover vitality.

However, there were numerous limitations in the study design, which casts doubt on the validity of the associations reported.

The results may not be applicable to the general population, as this was a selective group of participants who were:

  • active users of gaming websites
  • students of human psychology
  • able and happy to spend time filling out six questionnaires totalling 64 questions (which one could argue is another perfect way to avoid doing other activities)

There was a wide variation in the number of hours the participants had worked during the previous day, from half an hour to 16 hours.

It does not appear that potential confounding factors such as this were taken into account during the analyses.

The average age of the participants was not provided, nor were any other socioeconomic or demographic data.

There was no control group, as anyone who had not used either form of media was excluded from the study. People were only able to respond to either their use of TV or video games. We therefore can’t say whether use of one preceded another, how much time was actually spent on both or what the level of enjoyment or guilt was during that time.

The questionnaires were heavily loaded, suggesting that people should feel guilty for their TV and video game use and this would create a source of bias. Good surveys should address this issue with other questions to balance out their suggestive nature but it is not clear if this occurred.

There is also the possibility that the participants may have not answered truthfully, or skewed their answers in a way that was helpful, or even unhelpful, to the study organisers.

The questionnaires were self-reported and filled out online about the preceding day. This leaves room for inaccuracies in recall.

Overall, the results of this study are not reliable due to the extent of the limitations

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter. Join the Healthy Evidence forum.

Links To The Headlines

Watching TV after work makes you feel 'guilty and like a failure'. The Independent, July 25 2014

Tired? Then don't slump in front of TV: People who are stressed and exhausted end up being consumed with guilt after putting their feet up, study reveals. Daily Mail, July 25 2014

Why TV at the end of the day leaves workers feeling depressed. The Daily Telegraph, July 25 2014

Watching telly makes us feel like failures. Daily Express, July 25 2014

Links To Science

Reinecke L, Hartmann T, Eden A. The Guilty Couch Potato: The Role of Ego Depletion in Reducing Recovery Through Media Use. Journal of Communication. Published online June 24 2014

Categories: News