Daytime Eating May Cut Diabetes Risk in Night-Shift Workers

Marlene Busko

December 09, 2021

By only eating during the daytime, night-shift workers might avoid having a misaligned internal circadian clock and impaired glucose tolerance — which are typical in night-shift workers — a small clinical trial suggests.

Among 19 healthy young adults who spent 2 weeks in a controlled laboratory setting that included a simulated night shift, the nine individuals who ate their three meals and a snack during the day (7 AM to 7 PM) did not have a misaligned circadian rhythm or glucose intolerance, unlike the 10 individuals who ate the same food during the day and night.

The study was published December 3 in Science Advances.

The findings suggest that nighttime eating caused a misalignment between the body's central circadian "clock" (located in the hypothalamus) and sleep/wake, light/dark, and fasting/eating cycles that can influence peripheral "clocks" throughout the body.

"These results indicate that meal timing was primarily responsible for the reported effects on glucose tolerance and beta-cell function, possibly due to the misalignment of central and peripheral 'clocks' throughout the body," said senior author Frank A.J.L. Scheer, PhD.

"While the central circadian 'clock' was still on Boston time, the endogenous circadian glucose rhythms suggest that some peripheral 'clocks' — as perhaps those in the liver — had dramatically shifted to a time zone in Asia," explained Scheer, director of the Medical Chronobiology Program in the Division of Sleep and Circadian Disorders at Brigham and Women's Hospital, Boston, Massachusetts in a press release issued by the hospital.

Meal Timing Could Counteract Negative Effects of Night Shift

"This is the first study in humans to demonstrate the use of meal timing as a countermeasure against the combined negative effects of impaired glucose tolerance and disrupted alignment of circadian rhythms resulting from simulated night work," he added in a press release from the National Heart, Lung, and Blood Institute, the main study funder.

"Night-shift workers often reschedule their meal intake to the nighttime, as they are awake during those hours," lead author of the work, Sarah L. Chellappa, MD, PhD, added.

"This study reinforces the notion that when you eat matters for determining health outcomes such as blood sugar levels, which are relevant for night workers as they typically eat at night while on shift," said Chellappa, a researcher who previously worked with Scheer and is currently working in the nuclear medicine department at the University of Cologne, Germany.

"Our findings," the researchers summarize, "may help in the development of evidence-based circadian strategies (eg, timing of eating) to prevent glucose intolerance in individuals experiencing circadian rhythm disruption."

"Future translational studies with individuals undergoing real-life shift work schedules (eg, permanent, rotating or irregular night shifts, morning shifts, and evening shifts) are required to establish if our reported beneficial effects on glucose tolerance (as well as other health and performance outcomes) apply to this vulnerable population," they conclude.

Could Meal Timing Mitigate Effects of Shift Work?

Previous studies have shown that in night-shift workers the central circadian clock is misaligned with daily behaviors, and these individuals have impaired glucose tolerance and an increased risk of diabetes.

But it was not clear if avoiding nighttime eating might lessen this risk.

To investigate, researchers recruited 19 healthy young participants (12 men, seven women) for the clinical trial during 2015 to 2018.

Participants were a mean age of 26.5 years, had a mean body mass index of 22.7 kg/m2, and had an A1c between 4.9% and 5.4%.

They underwent a stringently controlled circadian laboratory protocol, where they remained in individual suites in an environment free of time cues. When they were not involved in study tasks, they could read, write, watch movies, or do crafts.

First, participants stayed awake for 32 hours in a highly controlled, dimly lit environment, where they kept constant body posture and consumed identical snacks every hour, as part of a "constant routine" protocol.

After that, they underwent simulated night-shift work. Participants in one group ate scheduled meals during the day and night. The other participants ate meals during the day only, aligned with the approximately 24-hour cycle of the central circadian "clock."

Participants then followed a second "constant routine" protocol to assess the aftereffects of the two different meal schedules on endogenous circadian rhythms.

During the simulated night shift, the average glucose levels of the participants who ate during the day and night increased by 6.4% from baseline, whereas these levels did not increase significantly in the participants who only ate during the day.

This study was funded by the National Institutes of Health, the Alexander von Humboldt Foundation, the American Diabetes Association, the Spanish Government of Investigation, Development and Innovation, the Autonomous Community of the Region of Murcia through the Seneca Foundation, and the Oregon Institute of Occupational Health Sciences. Scheer has reported receiving lecture fees from Bayer HealthCare, Sentara HealthCare, Philips, Vanda Pharmaceuticals, and Pfizer. Disclosures for the other authors are listed with the article.

Sci Adv. Published online December 3, 2021. Article

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