Dolly Parton once sang that working 9-5 is “all taking and no giving,” but working outside of these hours may take away much more – when it comes to our health, at least. A new study finds people who work shifts are more likely to have sleep problems than people who follow conventional work schedules, which may raise their risk of metabolic disorders such as obesity and diabetes.

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People who work shifts are at higher risk of sleep problems, which may be a driver of metabolic disorders including obesity and diabetes.

Lead investigator Dr. Marjory Givens, an associate scientist at the University of Wisconsin School of Medicine and Public Health in Madison, and colleagues published their findings in Sleep Health – a journal of the National Sleep Foundation.

The link between shift work and poor health is not new. In July 2014, a study linked shift work – particularly rotating shifts – to increased risk of type 2 diabetes, while a more recent study found people who work rotating night shifts for at least 5 years are at higher risk of all-cause and cardiovascular mortality.

Using 2008-12 data from the Survey of the Health Wisconsin (SHOW), Dr. Givens and colleagues set out to investigate the health implications of shift work further – specifically, how shift work affects sleep, weight and diabetes risk.

For SHOW, all participants were subject to home- and clinical-based physical assessments and interviews.

The team analyzed 1,593 participants who underwent a physical examination, using the data to calculate their body mass index (BMI) in order to establish their overweight or obesity status.

The data of a further 1,400 participants with type 2 diabetes was assessed. Their condition was determined by either a self-reported physician diagnosis or by the presence of glycated hemoglobin (HbA1c) in the blood at levels of 6.5% or higher at physical assessment.

The working patterns of participants were recorded during interviews.

Compared with individuals who worked traditional 9-5 schedules, those who worked shifts were more likely to be overweight, at 34.7% and 47.9%, respectively.

Shift workers were also more likely experience sleep problems than 9-5 workers. Around 23.6% of shift workers had insomnia, compared with 16.3% of people who worked standard hours. Insufficient sleep was reported by 53% of shift workers and 42.9% of 9-5 workers, while 31.8% of shift workers experienced excessive wake-time sleepiness, compared with 24.4% of 9-5 workers.

The researchers were not surprised that shift workers had more sleep problems. “Shiftwork employees are particularly vulnerable to experiencing sleep problems as their jobs require them to work night, flex, extended, or rotating shifts,” explains Dr. Givens.

“Shift workers are more commonly men, minorities, and individuals with lower educational attainment and typically work in hospital settings, production, or shipping industries,” she adds.

Further investigation revealed that the increase in sleep problems among shift workers correlated with an increase in obesity and diabetes, with this association being strongest among shift workers who reported insufficient sleep – defined as less than 7 hours each day.

This finding, the researchers say, indicates that by getting sufficient sleep, shift workers may be able to reduce their risk of obesity and diabetes.

Dr. Givens adds:

This study adds to a growing body of literature calling attention to the metabolic health burden commonly experienced by shift workers and suggests that obtaining sufficient sleep could lessen this burden.

More research in this area could inform workplace wellness or health care provider interventions on the role of sleep in addressing shift worker health disparities.”

The team notes, however, that the positive association between sleep problems and metabolic disorders among shift workers does not fully explain why shift work raises the risk of metabolic disorders.

While this study is strengthened by the fact it drew its conclusions from a population-based sample and objective markers of overweight and diabetes, the researchers say there are some limitations.

They did not account for confounding factors, for example, and sleep duration and sleep quality of participants was self-reported. Finally, the team says that because they used cross-sectional data, they are unable to establish a causal relationship between shift work and poor metabolic health.