Night and day: Circadian rhythms and glucose tolerance

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Science Translational Medicine  13 May 2015:
Vol. 7, Issue 287, pp. 287ec78
DOI: 10.1126/scitranslmed.aab3978

The time of day affects how our bodies manage glucose. People who work at night have an increased risk for developing type 2 diabetes—thought to be a result, at least in part, of the offset between a normal sleep/wake cycle and the sleep/wake pattern required for night work, a situation known as circadian misalignment. The human circadian rhythm arises from a complex interplay of brain and nonbrain oscillators with environmental and behavioral inputs (for example, night/day and when you eat). Now, Morris and colleagues demonstrate that a misaligned circadian system alters glucose tolerance to increase diabetes susceptibility.

The authors performed a prospective, within-participant, cross-over study in which 14 healthy adults experienced both normal sleep/wake cycles (alignment) and sleep/wake cycles offset by 12 hours, designed to mimic shift work (misalignment). For 8 days, glucose tolerance was assessed in response to identical meals eaten at the same time. The subjects had higher glucose after dinner and during the biological evening than after breakfast and in biological morning. These glucose levels were a result of lower insulin concentrations, suggesting reduced pancreatic β-cell function later in the day.

Independent of the circadian phase or meal status, circadian misalignment reduced glucose tolerance: with post-meal glucose being 6% higher in misaligned individuals, corresponding to 14% higher insulin and suggesting decreased glucose tolerance. Morris et al. conclude that the effect of the circadian system on glucose tolerance is driven by at least two distinct mechanisms: reduced β-cell function in the biological evening, and lower glucose tolerance when the circadian system is in misalignment.

A better understanding of glycemic control during circadian misalignment will help inform the design of behavioral or circadian strategies to reduce the risk of type 2 diabetes in shift workers.

C. J. Morris et al., Endogenous circadian system and circadian misalignment impact glucose tolerance via separate mechanisms in humans. Proc. Natl. Acad. Sci. U.S.A. 112, E2225–E2234 (2015). [Full Text]

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