Limiting food intake to daytime hours may mitigate cardiovascular risk factors associated with simulated night shift work, even in the presence of circadian misalignment.
Eating only during daytime hours prevented changes in heart rate variability and prothrombotic markers that typically occur when meals are consumed throughout both day and night under simulated night work conditions, according to the results of a randomized trial, published in Nature Communications.
The researchers randomly assigned 20 healthy non–shift workers to 2 simulated night work conditions: a control group that consumed meals during both daytime and nighttime (typical of shift workers) and an intervention group that consumed meals only during daytime hours. Nineteen participants completed the protocol (10 in the control group and 9 in the intervention group).
The participants underwent a 14-day in-laboratory protocol, including a forced desynchrony protocol that induced circadian misalignment similar to that experienced by shift workers. Cardiovascular measures were taken under "constant routine" conditions—periods of continuous wakefulness, dim lighting, limited posture changes, and hourly isocaloric snacks—prior to and following the simulated night work period.
Primary cardiovascular outcomes included measures of cardiac vagal modulation: the percentage of consecutive heartbeat intervals over 50 ms (pNN50), root mean square of successive differences between heartbeats (RMSSD), and low-frequency to high-frequency cardiac variability (LF/HF ratio). The secondary outcome was plasma concentrations of plasminogen activator inhibitor-1 (PAI-1), a prothrombotic factor regulated by the circadian system.
"In the control group, the postmisalignment constant routine showed a decrease in pNN50 by 25.7% (pFDR = 0.008) and RMSSD by 14.3% (pFDR = 0.02), and an increase in LF/HF by 5.5% (pFDR = 0.04) and PAI-1 by 23.9% (pFDR = 0.04) vs the baseline constant routine," the study authors reported. In contrast, "In the intervention group, there were no significant changes in these outcomes."
In the intervention group, blood pressure decreased following simulated night work exposure. “In the [daytime meal intervention] group, blood pressure levels significantly decreased by 6% [to] 8% after exposure to the simulated night work compared [with] baseline ([systolic blood pressure] = −6.1%, 95% [confidence interval] = −8.9% to −4.5%; [diastolic blood pressure] = −8.0%, 95% [confidence interval] = −9.1% to −6.9%; Tukey-Kramer post-hoc test adjusted for multiple comparisons, P = .005 and P = .001),” noted investigators. No significant change in blood pressure was observed in the control group.
The intervention did not significantly alter the effect of simulated night work on cortisol levels (P = .31) or heart rate (P = .36).
A daytime eating schedule may help offset some of the adverse cardiovascular effects of circadian misalignment. Approximately 15% of workers in industrialized countries perform night shift work, and extended duration of night shift work has been associated with increased coronary heart disease risk.
The researchers noted that their findings were consistent with previous preclinical data showing that a consistent 24-hour cycle of feeding and fasting can support cardiovascular health. In one cited study, limiting food intake to the daytime preserved cardiac tissue function in flies, regardless of diet composition.
Study limitations included a relatively small sample size, a restricted participant age range (18 to 30 years), and the use of simulated rather than real-world shift work. The study population consisted of healthy, non–shift workers in a controlled laboratory setting, which may have limited generalizability.
Disclosures can be found in the original article.