A study conducted by researchers at Mass General Brigham suggests that meal times may be a greater risk factor for cardiovascular health than bedtimes. Numerous studies have shown that night work is associated with serious health risks, including for the heart. However, a new study by Mass General Brigham suggests that people could avoid the health risks associated with shift work by eating only during daylight hours. The results were published in Nature Communications.

“Our previous research has shown that circadian misalignment—the misalignment of our behavioral cycle with our internal clock—increases the risk factors for cardiovascular disease,” said lead author Frank A.J.L. Scheer, PhD, 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 could be done to reduce this risk, and our new study suggests that meals may be a starting point.”

Cardiovascular Risk Factors from Eating at Night

Animal studies have shown that aligning meal times with the body’s internal clock may reduce the health risks of staying awake during typical rest periods. This prompted Scheer and his colleagues to test this concept in humans. For the study, the researchers recruited 20 healthy young participants for a two-week inpatient study at the Brigham and Women’s Center for Clinical Investigation. They had no access to windows, clocks, or electronic devices that could signal their internal clock. The effects of circadian misalignment were determined by comparing changes in their bodily functions before and after simulated night work.

The study participants followed a “constant routine protocol,” a controlled laboratory setup that separates the effects of the circadian rhythm from those of the environment and behavior (e.g., sleep/wake phases, light/dark phases). During this protocol, participants remained awake for 32 hours in a dimly lit environment, maintained a constant body posture, and ate identical snacks every hour. They then took part in simulated night work and were assigned to either the group that ate during the night (like most night workers) or the group that only ate during the day. Finally, participants followed another constant routine protocol to test the aftereffects of simulated night work. Importantly, both groups had an identical nap schedule so that differences between the groups were not due to different sleep habits. The researchers examined the aftereffects of meal times on participants’ cardiovascular risk factors and how these changed after simulated night work. The researchers measured various cardiovascular risk factors, including markers of the autonomic nervous system, plasminogen activator inhibitor-1 (which increases the risk of blood clots), and blood pressure.

Improving Health by Adjusting Meal Times

It is noteworthy that these cardiovascular risk factors increased after simulated night work compared to baseline in participants who were instructed to eat during the day and at night. However, risk factors remained unchanged in study participants who ate only during the day, even though the groups did not differ in terms of the amount and type of food consumed—only the timing of food intake differed. Limitations of the study include the fact that, although the sample size was typical for such strictly controlled and intensive randomized controlled trials, it was still small. Since the study lasted only two weeks, it may not reflect the chronic risks of eating at night compared to eating during the day.

One strength is that the sleep, diet, light exposure, posture, and activity schedule of the study participants were strictly controlled. “Our study controlled for all factors that could influence the results, so we can say that it is the timing of food intake that causes these changes in cardiovascular risk factors,” said Sarah Chellappa, MD, MPH, PhD, associate professor at the University of Southampton and lead author of the study. Although further research is needed to confirm the long-term health effects of eating during the day versus eating at night, Scheer and Chellappa describe the findings as “promising” and suggest that people may be able to improve their health by adjusting their eating times. They add that avoiding or limiting meals during nighttime hours may be beneficial for night shift workers, people with sleep disorders or sleep-wake disorders, individuals with irregular sleep-wake rhythms, and people who frequently experience jet lag.