Postprandial hormone and metabolic responses in simulated shift work

Abstract

This study was designed to investigate postprandial responses to a mixed meal in simulated shift work conditions. Nine normal healthy subjects (six males and three females) were studied on two occasions at the same clock time (1330 h) after consuming test meals, first in their normal environment and secondly after a 9 h phase advance (body clock time 2230 h). Plasma glucose, insulin, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), triacylglycerol (TAG) and non-esterified fatty acids (NEFAs) were determined at intervals for 6 h after each test meal. Postprandial plasma glucose, insulin, GIP and GLP-1 profiles were evaluated by calculating areas under the curve (AUC) for the first 2 h and the last 4 h of the sampling together with total AUC. Significantly higher postprandial glucose responses (total AUC) were observed after the phase shift than before (AUC 0-360 min, 2.01 (1.51-2.19) vs 1.79 (1.56-2.04) mmol/l.min; P < 0.02; mean (range)). No significant difference was observed when the first 2 h of each response was compared, but significantly higher glucose levels were observed in the last 4 h of the study after the phase shift than before (AUC 120-360 min, 1.32 (1.08-1.42) vs 1.16 (1.00-1.28) mmol/l.min; P < 0.05). Similar results were obtained for insulin (AUC 0-360 min, 81.72 (30.75-124.97) vs 58.98 (28.03-92.57) pmol/l.min; P < 0.01; AUC 120-360 min, 40.73 (16.20-65.25) vs 25.71 (14.25-37.33) pmol/l.min; P < 0.02). No differences were observed in postprandial plasma GIP and GLP-1 responses before and after the phase shift. Postprandial circulating lipid levels were affected by phase shifting. Peak plasma TAG levels occurred 5 h postprandially before the phase shift. Postprandial rises in plasma TAG were significantly delayed after the phase shift and TAG levels continued to rise throughout the study. Plasma postprandial NEFA levels fell during the first 3 h both before and after the phase shift. Their rate of return to basal levels was significantly delayed after the phase shift compared with before. This study demonstrates that a simulated phase shift can significantly alter pancreatic B-cell responses and postprandial glucose and lipid metabolism.

Endogenous circadian system and circadian misalignment impact glucose tolerance via separate mechanisms in humans

“…The present study showed that the adverse effects of circadian misalignment during a forced desynchrony protocol are also observed in conditions more similar to those experienced by real-life shift workers, and are sustained over a number of days of repeated exposure. Our data are also consistent with the general notion that various forms of circadian disruption (e.g., SCN lesions, clock gene mutations, continuous light exposure, and simulated shift work) can impair glucose metabolism (19,20,26,28,29).…”

“…An endogenous circadian rhythm in circulating glucose and insulin levels has been detected in humans by using intensive protocols performed under constant conditions ("constant routine" protocols) or when the behavioral cycle influences are accounted for by evenly distributing them across the entire circadian cycle ("forced desynchrony" protocols) (4,(10)(11)(12)14). In addition, circadian misalignment-as occurs in shift workers-also leads to impaired glucose metabolism in rodents and humans (10,(25)(26)(27)(28)(29)(30)(31)(32).…”

Adverse metabolic and cardiovascular consequences of circadian misalignment

“…Others have examined the effect of simulated night shift work on postprandial glucose and insulin with varied results (18,19). Interpretation of these studies is complicated due to differences in premeal conditions between the night and day shifts (e.g., duration of wakefulness before test meals), such that the effects of circadian misalignment alone could not be assessed.…”

Circadian regulation of lipid metabolism

“…Similarly, chronic exposure to shift work increases risk of metabolic syndrome (87) , as well as CHD, stroke and stroke-related mortality, and type 2 diabetes (88)(89)(90)(91) . Laboratory studies in human subjects have shown that consumption of meals during the biological night results in increased postprandial glucose, insulin and TAG relative to daytime meals (92)(93)(94) . Additionally, rotating shiftwork is associated with higher fasting TAG and free fatty acids, and lower HDLcholesterol (95,96) .…”