Altered postprandial hormone and metabolic responses in a simulated shift work environment

Abstract

The circadian rhythms of most night shift workers do not adapt fully to the imposed behavioural schedule, and this factor is considered to be responsible for many of the reported health problems. One way in which such disturbances might be mediated is through inappropriate hormonal and metabolic responses to meals, on the night shift.Twelve healthy subjects (four males and eight females) were studied on three occasions at the same clock time (1330 h), but at different body clock times, after consuming test meals, first in their normal environment, secondly after a forced 9 h phase advance (body clock time approximately 2230 h) and then again 2 days later in the normal environment. They were given a low-fat pre-meal at 0800 h, then a test meal at 1330 h with blood sampling for the following 9 h. Parameters measured included plasma glucose, non-esterified fatty acids (NEFAs), triacylglycerol (TAG), insulin, C-peptide, proinsulin and glucosedependent insulinotropic polypeptide, and urinary 6-sulphatoxymelatonin.In contrast with a previous study with a high-fat premeal, postprandial glucose and insulin responses were not affected by the phase shift. However, basal plasma NEFAs were lower immediately after the phase shift (P<0·05). Incremental (difference from basal) TAG responses were significantly higher (P<0·05) immediately after the phase shift compared with before. Two-day post-phase shift responses showed partial reversion to baseline values.This study suggests that it takes at least 2 days to adapt to eating meals on a simulated night shift, and that the nutritional content of the pre-meals consumed can have a marked effect on postprandial responses during a simulated phase shift. Such findings may provide a partial explanation for the increased occurrence of cardiovascular disease reported in shift workers.

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) .…”

Sleep, circadian rhythm and body weight: parallel developments

“…Disruption of the circadian system affects metabolic and cardiovascular changes (2,45,(96)(97)(98) . In relation to appetite, release of some endocrine products shifts with meal patterns, such as glucose, insulin, GLP-1, ghrelin and leptin concentrations.…”

“…Also examples of long-term responses to a sustained regular meal frequency such as improved glucose tolerance, and moderately reduced fasting plasma total and LDL-cholesterol, and a higher HDL:LDL cholesterol ratio are observed in normolipidaemic free-living subjects, as well as in type-II diabetes patients (103)(104)(105)(106)(107)(108)(109)(110)(111) . Also for cholesterol synthesis, meal frequency-dependent control of cholesterogenesis appeared to be mediated via hormonal mechanisms (97) .…”