Effects of bergamot aromatherapy on sleep: A placebo-controlled trial

Delayed sleep timing from pre-bedtime smartphone use impairs student sleep quality. While aromatherapy is widely used for sleep improvement, its efficacy under different sleep timing remains unclear, and placebo-controlled polysomnography (PSG) evidence is scarce. In a crossover trial, 15 healthy male students (intermediate chronotype) underwent four conditions: normal sleep (NS) and delayed sleep (DS), each with placebo or bergamot. All conditions allowed 8 hours of sleep opportunity. PSG, heart rate variability, and subjective questionnaires were measured. Two-way repeated measures ANOVA examined main and interaction effects. The key finding was a significant sleep timing × aromatherapy interaction (p < 0.05), indicating bergamot’s benefits amplified under delayed sleep. Specifically, bergamot improved sleep efficiency by 8.43% under delayed sleep versus 4.85% under normal sleep (interaction p < 0.05), and reduced wake after sleep onset by 34.7 min vs 17.5 min (both p < 0.01; interaction p < 0.05). State anxiety decreased significantly (p < 0.001). Significant interactions for positive and negative affect (both p < 0.05) showed divergent patterns: positive affect improved more under normal sleep, while negative affect reduced more under delayed sleep. N-back accuracy increased by 5% (p = 0.001). Sleep architecture remained unchanged, suggesting bergamot enhances sleep continuity rather than altering sleep stage distribution. Bergamot enhances sleep continuity and next-day cognition, with more pronounced effects under delayed sleep. Although this intervention shows promise for mitigating subclinical sleep disruption, its relative efficacy compared to established behavioral and environmental strategies, and individual variability in olfactory tolerance, need further investigation.