Eating only during the daytime could protect people from heart risks of shift work

A new study involving the University of Southampton suggests that, when it comes to cardiovascular health, food timing could be a big risk factor.

Numerous studies have shown that working night shifts is associated with serious health risks, including to the heart. Now a new study, led by Mass General Brigham in the United States, suggests that eating only during the daytime could help people avoid the health risks associated with shift work.

The results are published today [8 April 2025] in Nature Communications.

“Our prior research has shown that circadian misalignment – the mistiming of our behavioural cycle relative to our internal body clock – increases cardiovascular risk factors,” said senior author Professor Frank A.J.L. Scheer , a professor of Medicine and director of the Medical Chronobiology Program at Brigham and Women’s Hospital, a founding member of the Mass General Brigham healthcare system.

“We wanted to understand what can be done to lower this risk, and our new research suggests food timing could be that target.”

Animal studies have shown that aligning food timing with the internal body clock could mitigate the health risks of staying awake during the typical rest time, which prompted the researchers to test this concept in humans.

Researchers enlisted 20 healthy young participants for a two-week in-patient study at the Brigham and Women’s Center for Clinical Investigation. They had no access to windows, watches, or electronics that would clue their body clocks into the time. The effect of circadian misalignment could be determined by comparing how their body functions changed from before to after simulated night work.

“Our study controlled for every factor that you could imagine that could affect the results, so we can say that it’s the food timing effect that is driving these changes in the cardiovascular risk factors,” said Dr Sarah Chellappa , an associate professor at the University of Southampton, and lead author for the paper.

Study participants followed a ‘constant routine protocol,’ a controlled laboratory setup that can tease apart the effects of circadian rhythms from those of the environment and behaviours (e.g., sleep/wake, light/dark patterns). During this protocol, participants stayed awake for 32 hours in a dimly lit environment, maintaining constant body posture and eating identical snacks every hour.

After that, they participated in simulated night work and were assigned to either eating during the nighttime (as most night workers do) or only during the daytime. Finally, participants followed another constant routine protocol to test the aftereffects of the simulated night work. Importantly, both groups had an identical schedule of naps, and, thus, any differences between the groups were not due to differences in sleep schedule.

The investigators examined the aftereffects of the food timing on participants’ cardiovascular risk factors and how these changed after the simulated night shift. Researchers measured various cardiovascular risk factors, including autonomic nervous system markers, plasminogen activator inhibitor-1 (which increases the risk of blood clots), and blood pressure.

Remarkably, these cardiovascular risk factors increased after simulated night work compared to the baseline in the participants who were scheduled to eat during the day and night. However, the risk factors stayed the same in the study participants who only ate during the daytime, even though how much and what they ate was not different between the groups - only when they ate.

The sample size of the study was small, although of a typical size for such highly controlled and intensive randomized controlled trials. Moreover, because the study lasted two weeks, it may not reflect the chronic risks of nighttime versus daytime eating.

While further research is necessary to show the long-term health effects of daytime versus nighttime eating, Scheer and Chellappa said the results are “promising” and suggest that people could improve their health by adjusting food timing.

They add that avoiding or limiting eating during nighttime hours may benefit night workers, those who experience insomnia or sleep-wake disorders, individuals with variable sleep/wake cycles, and people who travel frequently across time zones.

Daytime eating during simulated night work mitigates changes in cardiovascular risk factors: secondary analyses of a randomized controlled trial is published in Nature Communications and is available online.

The research was funded by the National Institutes of Health (NIH) in the United States.