Differential effects of the circadian system and circadian misalignment on insulin sensitivity and insulin secretion in humans.
Level 2 - randomized trial
Randomized crossover laboratory trial
PubMed 29862620 · doi:10.1111/dom.13391
What was done
Fourteen healthy adults completed a randomized crossover study consisting of two 8-day inpatient laboratory protocols. Each protocol included 3 baseline days with habitual sleep/wake schedules, followed by 4 days of either standard nocturnal sleep (circadian alignment) or a 12-hour inverted behavioral and environmental cycle (circadian misalignment). Glucose tolerance, insulin sensitivity, and dynamic and static beta-cell function were quantitatively assessed using the oral minimal model.
What was found
The endogenous circadian system and circadian misalignment impaired glucose tolerance via distinct physiological pathways. The internal circadian phase decreased glucose tolerance during the biological evening compared to the biological morning predominantly by reducing both dynamic and static beta-cell responsivity. In contrast, circadian misalignment impaired glucose tolerance primarily by decreasing insulin sensitivity rather than affecting beta-cell function. The abstract did not report specific numerical values or effect sizes.
Why it matters
These findings delineate the distinct physiological mechanisms through which internal biological timing and shift-work-like behavioral inversion independently impair glucose regulation, helping explain the elevated type 2 diabetes risk in shift workers.
Limits
The study was conducted in a very small sample (n = 14) of healthy individuals under tightly controlled inpatient conditions, which may not capture chronic, real-world shift-work exposures. The abstract provides qualitative directional findings without quantitative effect estimates or variance measures.
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