Daytime eating may protect heart health in night shift workers

Key Points:

• A new study from Mass General Brigham finds that when we eat may matter more than when we sleep for cardiovascular health.

• Daytime eating during simulated night shifts prevented increases in heart risk factors, even without changing sleep patterns.

• The findings may help protect night workers and frequent travelers from the cardiovascular risks linked to circadian disruption.

A groundbreaking new study suggests that eating only during daytime hours may shield night shift workers from serious heart health risks, offering a potential new strategy to counter the well-known dangers of circadian disruption.

Led by researchers at Mass General Brigham and published in Nature Communications, the study found that daytime eating prevented increases in key cardiovascular risk markers, even when participants were exposed to simulated night work and experienced disrupted sleep-wake cycles.

“This is the strongest evidence yet that meal timing—not just what you eat—plays a critical role in heart health, especially for people with irregular schedules,” said Dr. Frank A.J.L. Scheer, senior author and director of the Medical Chronobiology Program at Brigham and Women’s Hospital.

Testing food timing under strict conditions

The study followed 20 healthy young adults through a two-week, tightly controlled lab protocol. Participants were isolated from all time cues—no clocks, phones, or windows—and placed under a “constant routine” protocol to measure the effects of circadian misalignment.

After 32 hours of wakefulness under controlled conditions, participants entered a phase simulating night shift work. Half were assigned to eat during the night, as shift workers commonly do, while the other half only ate during daytime hours. Both groups received the same amount and type of food, and their sleep and activity levels were identical.

Heart risk spiked unless eating was daytime-only

The results were striking: participants who ate both day and night showed increased markers of cardiovascular risk, including:

• Higher blood pressure

• Increased plasminogen activator inhibitor-1, a protein that raises blood clot risk

• Altered autonomic nervous system activity

In contrast, participants who only ate during the day showed no change in these risk markers, despite undergoing the same sleep disruption and simulated night shifts.

“This is the first human study to isolate food timing as the key variable,” said Dr. Sarah Chellappa, lead author and associate professor at the University of Southampton. “We controlled everything else—sleep, posture, light, activity—so we know it’s the meal timing driving these effects.”

Implications for millions of shift workers

More than 16 million Americans work night shifts, and many more experience circadian disruption from frequent travel or irregular schedules. These populations face higher risks of obesity, diabetes, and heart disease—but this study offers hope.

While the researchers acknowledge the small sample size and short duration as limitations, they say the findings are promising and warrant larger, long-term studies.

For now, Scheer and Chellappa recommend that shift workers and night owls avoid eating late at night, suggesting that meal timing may be a powerful, practical tool for improving heart health—even when sleep schedules can’t change.