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Circadian misalignment reduces glucose tolerance in shift workers
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In shift workers, circadian misalignment appears to cause a decrease in glucose tolerance, independent of behavioral or circadian phase effects, according to recent findings.
Christopher J. Morris, MSc, of the division of sleep and circadian disorders at Brigham and Women’s Hospital in Boston, and colleagues evaluated nine healthy, nonsmoking, drug- and medication-free adults (mean age, 34 years; BMI, 24.2 kg/m2) to determine whether the endogenous circadian system and circadian misalignment separately affect glucose tolerance in shift workers independent of behavioral cycle effects.
Each participant underwent two 3-day laboratory protocols. One protocol, designated a “circadian alignment protocol,” involved the simulation of a day shift; the other, “circadian misalignment protocol,” involved a simulated night shift. The protocols were separated by 3 to 8 weeks. Researchers measured postprandial glucose and insulin responses to identical meals given at 8 a.m. and 8 p.m. in both protocols.
Postprandial glucose was 6% higher in the biological evening compared with the biological morning (P = .004) suggesting relatively decreased glucose tolerance in the biological evening.
In the early-phase postprandial period, postprandial insulin was 18% lower in the biological evening compared with the morning (P = .011) suggesting lower beta-cell function in the biological evening. Additionally, late-phase postprandial insulin was 18% lower in the biological evening compared with the morning (P < .0001), adding to the evidence of inadequate beta-cell function in the biological evening.
During the circadian misalignment state, postprandial glucose was 6% higher vs. in the alignment condition (P = .004). Compared with the alignment condition, late-phase postprandial insulin was 10% higher in the misalignment condition (P = .015) indicating reduced insulin sensitivity in the misalignment state. Circadian misalignment did not appear to significantly influence fasting glucose or insulin or 24-hour glucose or insulin area under the curves (AUCs). Total sleep time was decreased by 123 minutes during sleep opportunities prior to test meals in circadian misalignment (P = .005).
“We have tested the separate effects of the behavioral cycle, circadian phase and circadian misalignment on glucose and insulin responses to test meals in shift workers,” the researchers wrote. “We found that glucose tolerance is lower in the biological evening than morning, independent of behavioral cycle effects. This suggests that the internal circadian time of food intake may be an important factor to consider in shift workers. The circadian effect on glucose tolerance seemed to be partly explained by lower beta-cell function in the biological evening than biological morning.” – by Jennifer Byrne
Disclosure: The researchers report no relevant financial disclosures.
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