Bloodstream glucose levels can be regulated with daytime meal in night shift workers

What are the consequences of eating at night instead of during the day? New research focusing on a simulation of night shift work may have ramifications for those who eat at unusual hours, such as those suffering from jet lag, circadian rhythm sleep problems, or who sleep late on weekends.

A study by investigators from Brigham and Women’s Hospital indicates eating during the nighttime can lead to glucose intolerance, while limiting meals to the daytime can help regulate bloodstream glucose levels. Nighttime eating appeared to cause a misalignment between the body’s central and peripheral circadian “clocks” -; natural timekeepers that regulate physical, mental and behavioral changes over a 24-hour cycle. The researchers’ results are published in Science Advances.

Glucose intolerance leads to high glucose levels and often precedes type 2 diabetes mellitus (T2DM), a condition in which the body is less able to absorb sugar from the bloodstream into its tissues. T2DM is prevalent among night shift workers who typically sleep during the daytime and eat during the nighttime. Previous laboratory studies showed increased levels of blood glucose in both non-shift workers and shift workers who underwent simulated night work, said co-corresponding author Sarah L. Chellappa, MD, PhD, formerly of the Medical Chronobiology Program and now of the Department of Nuclear Medicine at the University of Cologne in Germany. They added that shift workers, while frequently exposed to mistimed meals, are not necessarily “immune” to their adverse effects.

This study, a randomized controlled trial, involved 19 healthy young participants who underwent a 14-day controlled laboratory protocol. During the study, participants stayed awake for 32 hours in a highly controlled, dimly lit environment, where they kept constant body posture, consumed identical snacks every hour, and had no time cues -; conditions that are part of a constant routine protocol.

After that, the participants underwent simulated night work and followed one of two eating schedules: one group ate during the nighttime to simulate a schedule typical among night shift workers, while the other group ate during the daytime, thus aligning their meal schedule to the ~24-hour cycle of the central circadian “clock.” Subsequently, participants followed a second, 40-hour constant routine protocol to assess the aftereffects of the meal schedules on their endogenous circadian rhythms.

According to the research, participants who ate during the nighttime showed increased blood glucose levels, while those who ate only during the daytime showed no significant changes. In addition, nighttime eating decreased pancreatic beta-cell function compared to no observable changes in those eating only during the daytime.

Beta cells produce insulin, a hormone that escorts glucose into body tissues. Furthermore, nighttime eating caused a misalignment between the central circadian “clock,” estimated from the endogenous circadian rhythm in core body temperature, and the endogenous circadian glucose rhythms. In stark contrast, these rhythms remained aligned when participants ate meals only during the daytime despite their mistimed sleep.

“Of the participants studied, those with the biggest disruption of their circadian system -; here quantified as the misalignment between their central circadian ‘clock’ and their endogenous circadian glucose rhythms -; showed the largest impairment of glucose tolerance,” said Scheer.

The study’s take-home message indicates that daytime eating, despite mistimed sleep, maintains internal circadian alignment and prevents glucose intolerance. The authors note that more research needs to be conducted to find practical interventions to implement daytime eating in real-life shift workers.