Eating at the right time of day may be more important for heart health than sleep timing, especially for people working night shifts.
A highly controlled study found that participants who ate only during the daytime avoided the cardiovascular risks typically seen with night shift work. Despite identical diets and sleep schedules, only those who ate at night saw increases in blood pressure and other risk markers. This suggests that when we eat might have a bigger impact on our heart than previously thought, potentially offering a new strategy for shift workers and frequent travelers to protect their health.
Food Timing vs. Sleep Timing in Heart Health
New research led by scientists at Mass General Brigham suggests that when you eat may be more important for heart health than when you sleep.
While previous research has linked night shift work to serious health issues, including an increased risk of heart disease, this study found that eating only during the daytime may help reduce those risks, even for people who work overnight. The findings were published today (April 8) in Nature Communications.
Circadian Misalignment and Cardiovascular Risk
“Our prior research has shown that circadian misalignment – the mistiming of our behavioral cycle relative to our internal body clock – increases cardiovascular risk factors,” said senior author Frank A.J.L. Scheer, PhD, 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.”
Previous animal studies hinted that eating in sync with the body’s internal clock could reduce the health impacts of being awake at night. That promising evidence led Scheer and his team to explore the idea in humans for the first time.
Controlled Study Design to Mimic Night Work
For the study, researchers enlisted 20 healthy young participants to 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.
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 behaviors (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.
Daytime Eating Prevents Cardiovascular Risk Spike
The investigators examined the aftereffects of the food timing on participants’ cardiovascular risk factors and how these changed after the simulated night work. 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.
Short Duration and Small Sample, But High Control
Limitations of the study include that the sample size 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.
A strength is that the study participants’ sleep, eating, light exposure, body posture, and activity schedule were so tightly controlled.
“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 Sarah Chellappa, MD, MPH, PhD, an associate professor at the University of Southampton, and lead author for the paper.
Who Might Benefit From This Approach
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.
Reference: “Daytime eating during simulated night work mitigates changes in cardiovascular risk factors: secondary analyses of a randomized controlled trial” by Sarah L. Chellappa, Lei Gao, Jingyi Qian, Nina Vujovic, Peng Li, Kun Hu and Frank A.J.L. Scheer, 8 April 2025, Nature Communications.
DOI: 10.1038/s41467-025-57846-y
In addition to Scheer, Mass General Brigham authors include Lei Gao, Jingyi Qian, Nina Vujovic, Peng Li, and Kun Hu.
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