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Daytime meals may reduce health risks of night shift work

Adjusting the timing of meals may help offset some of the health effects of night shift work. TZIDO SUN / Shutterstock

Night shift work disrupts the body’s circadian rhythms, or 24-hour internal “clock” that controls sleep-wake cycles. It increases the risk of developing diabetes, heart disease, and obesity. Studies have shown that eating at night, as many nightshift workers do, impairs the body’s ability to process sugar, or glucose.

Animal studies suggested there might be a way to counteract the negative effects of night shift work on metabolism: limit eating to daytime. A team of researchers led by Drs. Sarah Chellappa, now at the University of Cologne in Germany, and Dr. Frank A.J.L. Scheer of Harvard Medical School and Brigham & Women’s Hospital studied whether the timing of meals could prevent night shift’s adverse effects on blood sugar.

The study was funded by NIH’s National Heart, Lung, and Blood Institute (NHLBI), National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), and National Center for Advancing Translational Sciences (NCATS). Results appeared in Science Advances on December 3, 2021.

The team enrolled 19 healthy young participants, seven women and 12 men. They first tested baseline circadian rhythms using extended periods of wakefulness and dim light. The participants were then randomly assigned to receive one of two meal schedules while undergoing simulated night work conditions for 14 days. One group ate to mimic a schedule typical among night workers, with meals during both the daytime and nighttime. The other group ate only during the daytime.

The researchers then evaluated the effects of these meal schedules on circadian rhythms and metabolism. They found that nighttime eating boosted glucose levels, which is a risk factor for diabetes. Restricting meals to the daytime prevented this effect. Average glucose levels for those who ate at night increased by 6.4% during the simulated night work. In contrast, those who ate during the daytime showed no significant increases in glucose.

The team also found that eating breakfast after waking at night significantly affected insulin levels during the night shift schedule, but eating breakfast during daytime did not. Insulin signals cells to take in glucose, and diabetes often results from problems processing insulin.

This study is the first to demonstrate the health benefits of exclusive daytime eating during night shift work in humans. The researchers believe that the effects on glucose can be explained by “circadian misalignment.” This is the mistiming between the central circadian clock in the brain and other cycles, such as sleeping and waking, light and dark, and fasting and eating. Misalignment can arise between the central circadian clock and other systems throughout the body, including control of the metabolic system.

Better alignment between the central and peripheral clocks may explain the beneficial effects of daytime eating on glucose levels during night work.

“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,” Chellappa says.

Additional studies with real-life shift workers will be needed to further test the benefits of adjusting meal timing.