night shifts

Previous studies have shown that prolonged shift work is associated with a number of risks and diseases. In a recent study published in PLOS One, researchers sought to identify possible associations between night shifts and obesity risk.

Irregular and lengthy periods of shift work, especially night shifts, have been related to increased risk of obesity, cardiovascular disease, and some cancers. In countries like China, where obesity has increased drastically over the past couple of decades, the demand for night shifts because of industrialization has also increased rapidly. Some studies suggest that night shifts may be related to increased weight. Disorganization in the body’s internal “clock” has been suggested as a key mechanism of the association between night shifts and obesity. However, evidence for the link between irregular night shifts and obesity is still limited.

A Chinese research team recently conducted a study in order to better understand the association between shift work, especially night shifts, and obesity in a prospective cohort study. Their results were recently published in PLOS One.

For the study, they recruited a total of 3,871 workers from five different Chinese companies in 2013. They collected information regarding occupation, socio-demographics, smoking and drinking habits, diet, physical activity, sleep habits, and mental stress through a questionnaire. They also collected data on participants’ height, weight and measurements for waist and hip. Participants were also asked to give a statement on their work history, including how long they had been working shifts.

Among night-shift workers, researchers categorized the participants as permanent, rotating, or irregular night-shift workers. The research team also categorized participants into those who had worked night shifts for less than 5 years, between 5 and 10 years, or more than 10 years. A number of statistical models were used to measure the association between night shift work and obesity.

Night-shift workers had an increased risk of obesity

The study found night shift workers, in general, had an increased risk of obesity. In particular, abdominal obesity had a significant association with working night shifts. In addition, the study found that the longer that participants had been night shift workers, the more likely that they were obese.

Interestingly, permanent night-shift workers demonstrated the highest risk of obesity, while irregular night shift workers also showed significant association with obesity. There was no association between night shifts and obesity in participants that worked rotating night shifts.

Therefore, it seems that night shifts, whether they’re permanent or irregular can have detrimental effects to an individual’s health, particularly to obesity, which is a known risk factor for a host of other disorders and diseases. It will be interesting to see how these results fare to prospective cohort studies. These results may also hint at possibly switching shift workers to rotating night shift work at these companies.

Written by Ingrid Qemo, PhD

Reference: Sun, M., Feng, W., Wang, F., et al. 2018. Night shift work exposure profile and obesity: baseline results from a Chinese night shift worker cohort. PLOS One. 13;5.  doi: 10.1371/journal.pone.0196989

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