Aligning Meals With Body Clock Could Ease Heart Risks

When it comes to cardiovascular health and shift work, when you eat may be as important as what you eat.

People who work night shift are known to be at risk for coronary heart disease and other potentially serious medical conditions. A new study, by researchers from Mass General Brigham in Boston, found restricting meals to the daytime could help avoid such problems.

“One way to understand our finding is that our body’s internal clock is exquisitely organized to optimally coordinate virtually all aspects of our physiology with predictable cycling demands of the day and night,” said Frank A.J.L. Scheer, PhD, a professor of medicine and director of the Medical Chronobiology Program at Brigham and Women’s Hospital, Boston.

Most people maintain the standard, synchronized cycle of sleeping and waking up, engaging in activity and resting, as well as eating and fasting, all in time with the rising and setting of the sun. “If we eat when our circadian system is supporting sleep, rest, and fasting, our organ systems are ill-equipped to cope with that,” Scheer said. “This is most obvious for metabolic processes such as blood sugar regulation but holds true for cardiovascular function as well.”

For the new study, published in Nature Communications, Scheer and his colleagues tracked 19 healthy men and women (age, 22-30 years) in a 2-week in-patient experiment.

To ensure simulated night work was the only outside influence on the participants’ sleep cycle, Scheer and his colleagues imposed stringent restrictions on their behavior.

Participants had no access to windows, watches, or electronic devices that could clue their body clocks to the real time. They stayed awake for 32 hours in a dimly lit environment, eating identical snacks every hour. Afterward they engaged in simulated night work and were assigned to eat during the nighttime or only during the daytime.

The participants were then introduced to another routine to test the aftereffects of the simulated night work.

The primary outcomes were the percentage of consecutive heartbeat intervals > 50 ms (pNN50), the root mean square of successive heartbeat differences (RMSSD), and low/high cardiac frequency (LF/HF) ratio (< 60 beats/min and > 100 beats/min). The secondary outcome was blood concentrations of prothrombotic factor plasminogen activator inhibitor 1 (PAI-1).

Meal timing significantly modified the effect of simulated night work on cardiac vagal modulation and PAI-1 (P = .001). For those whose timing of meals was manipulated, pNN50 fell by 25.7% (P = .008) and RMSSD by 14.3% (P = .02). Meanwhile, this group experienced an increase in LF/HF ratio by 5.5% (P = .04) and PAI-1 by 23.9% (P = .04).

Nighttime meals also modified the effect of simulated shift work on blood pressure (P < .05), which dropped between 6% and 8% (P < .01).

“We hypothesized that maintaining the time of eating synchronized with the circadian system may alleviate the adverse effects of simulated night work on cardiovascular risk factors,” Scheer said. “We were amazed that meal timing could mitigate adverse effects even though sleep was still mistimed.”

Scheer and his team hope next to investigate the effects of meal timing in a more realistic simulation of a night shift. “These follow-up studies will help in the development of evidence-based countermeasures using food timing to improve cardiovascular health in shift workers and other populations with irregular behavioral rhythms,” he said.