Objective: Shift workers typically experience misalignment between their circadian system and behavioral/environmental cycles and have an increased risk for obesity. Experimental studies in non-shift workers have suggested that circadian misalignment can disrupt energy balance regulation. This study examined the impact of circadian misalignment in the most relevant population, i.e., chronic shift workers.
Methods: Seven healthy chronic night shift workers underwent a randomized crossover study with two 3-day laboratory protocols: a night work protocol including 12-hour inverted behavioral/environmental cycles (circadian misalignment) and a day work protocol (circadian alignment).
Results: Circadian misalignment led to a ~17% increase in 24-hour acylated ghrelin levels in the chronic shift workers (p = 0.009). Consistently, circadian misalignment resulted in ~14% higher hunger at breakfast in the night shift (p = 0.04). Circadian misalignment did not significantly change fasting and postprandial energy expenditure or respiratory exchange ratio (all p > 0.32). Unexpectedly, 24-hour behavioral activity levels were ~38% higher (p < 0.0001) during circadian misalignment, despite a concurrent increase in sleepiness (p = 0.03).
Conclusions: These results reveal that circadian misalignment, while carefully controlling for dietary intake, increases acylated ghrelin in chronic shift workers. Further studies should test whether the observed acute effects of circadian misalignment in chronic shift workers contribute to their increased obesity risk in the long term.
© 2023 The Obesity Society.