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The question

For millions of Americans, the workday is actually at night, either regularly or off and on. Might this have an effect on their weight?

This study

The researchers analyzed data from 28 studies, involving more than 270,000 people who worked various shifts in such sectors as health care, government, manufacturing, telecommunications and transit. Overall, comparing those who worked nights with those who did not, obesity was 23 percent more likely among night workers, especially if they worked night shifts long-term. People who worked nights all the time had a 43 percent increased risk for being overweight or obese, compared with a 14 percent increased risk for those who worked nights now and then. Among those overweight or obese, abdominal obesity was the most common type.

Who may be affected?

People whose work involves regular or rotating night shifts, estimated to be 20 percent of the workforce worldwide. Disrupted sleep is most often mentioned as the biggest downside of night work, but studies have also linked working nights, as well as working rotating shifts, to an increased risk for heart disease, diabetes, digestive problems and mental health issues.

Caveats

The study evaluated associations between night work and obesity; it did not prove that working nights was the cause of people’s excessive weight.

Find this study

Online Oct. 4 in Obesity Reviews (onlinelibrary.wiley.com; check “Publications” and search for “Obesity Reviews”; click on the journal title, then on “Early View”).

Learn more

Information on the health risks linked to shift work can be found at iwh.on.ca (search for “At Work 60,” then click on “Shift work and health”). To learn about the health effects of being overweight, go to niddk.nih.gov (search for “overweight”).

The research described in Quick Study comes from credible, peer-reviewed journals.