Daytime Eating May Reduce Heart Risks for Shift Workers
Eating only during the day may help reduce cardiovascular risks linked to disrupted sleep or shift work.
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A new study led by researchers at Mass General Brigham indicates that eating during daylight hours, rather than at night, may help reduce cardiovascular risk factors associated with shift work. The findings, published in Nature Communications, suggest that food timing may play a more significant role in cardiovascular health than sleep timing.
Study design isolates the effect of meal timing
The study involved 20 healthy young adults who took part in a highly controlled two-week inpatient protocol at the Brigham and Women’s Center for Clinical Investigation. The participants were kept in an environment devoid of natural light and external time cues, including access to clocks and electronic devices. This setting allowed researchers to isolate the effects of circadian rhythm misalignment on cardiovascular function.
Circadian misalignment
A mismatch between a person's internal biological clock and external behavioral cycles, such as sleeping during the day and staying awake at night. This misalignment can disrupt various physiological processes.“Our prior research has shown that circadian misalignment – the mistiming of our behavioral cycle relative to our internal body clock – increases cardiovascular risk factors. We wanted to understand what can be done to lower this risk, and our new research suggests food timing could be that target.”
Dr. Frank A.J.L. Scheer.
Participants followed a “constant routine protocol,” a method used in chronobiology to control for external variables such as sleep, light and physical activity. During this phase, they stayed awake for 32 hours in dim light, maintained consistent posture and consumed the same snacks hourly.
Constant routine protocol
A research method used to eliminate external influences and isolate the effects of the internal circadian system. Participants are kept awake under constant conditions, including lighting, posture and food intake.After this phase, participants underwent simulated night work. They were randomly assigned to one of two groups: one that ate during both day and night, and another that only ate during daytime hours. Both groups had identical nap schedules to eliminate sleep duration as a variable.
Daytime eaters showed no increase in cardiovascular risk factors
Following the simulated night work, researchers measured several cardiovascular risk indicators, including blood pressure, plasminogen activator inhibitor-1 levels and autonomic nervous system activity. These metrics typically rise when circadian rhythms are disrupted.
Plasminogen activator inhibitor-1 (PAI-1)
A protein that regulates blood clot breakdown. Elevated levels of PAI-1 can increase the risk of blood clots and have been associated with cardiovascular disease.Autonomic nervous system
A part of the nervous system that controls involuntary bodily functions, including heart rate and blood pressure. It plays a key role in the body’s response to stress and environmental changes.In participants who ate both during the day and night, these risk factors increased after the simulated night work. However, in those who ate only during the daytime, the values remained stable. This occurred despite both groups consuming the same foods in identical amounts, suggesting that the timing of eating was the primary variable influencing outcomes.
Controlled environment strengthens findings, but sample size limits scope
One of the study’s strengths lies in the strict control of environmental and behavioral variables. These measures support the conclusion that meal timing alone accounted for the observed differences.
“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."
Dr. Sarah Chellappa.
Nonetheless, the researchers acknowledge the limitations of the small sample size and the short two-week duration of the study. These factors mean the long-term cardiovascular effects of daytime versus nighttime eating remain unclear.
Implications for shift workers and individuals with disrupted sleep cycles
While further studies are needed to explore the long-term impact, the findings suggest that avoiding food during nighttime hours could benefit people working nontraditional hours, as well as those with irregular sleep-wake cycles or frequent jet lag.
Reference: Chellappa SL, Gao L, Qian J, et al. Daytime eating during simulated night work mitigates changes in cardiovascular risk factors: secondary analyses of a randomized controlled trial. Nat Comm. 2025;16(1):3186. doi: 10.1038/s41467-025-57846-y
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