Purpose: The objective of this study was to conduct a systematic review and meta-analysis to examine the effects of aromatherapy on sleep improvements. Methods: A search of randomized controlled trials was conducted in four English and two Chinese medical electronic databases. Two authors independently performed the search, assessed the methodological quality, and extracted data. Then, final studies were selected after consensus with the third author. Results: In total, 31 trials met the inclusion criteria, of which four had low risk, while the overall bias in 26 was uncertain in terms of methodological quality. The heterogeneity was high among the trials (Q = 341.544, p < 0.001, I2 = 91.216%). There was a significant effect of aromatherapy on sleep quality (Hedges's g = 1.103 (95% confidence interval: 0.813˜1.393, p < 0.001). There was a publication bias (Egger's regression intercept = 7.127, t = 3.055, p = 0.004 and Begg test, Kendall's tau with continuity correction, tau = 0.335 and Z = 2.651, p = 0.008). The subgroup analysis showed that there was a significant difference in the methodological quality among different studies (Q = 18.350, p < 0.001). Sensitivity analyses still revealed high heterogeneity after omitting one study at a time. Conclusions: The results showed that aromatherapy can be applied by clinical staff to effectively improve sleep quality. However, because there was a high degree of heterogeneity among studies, the inferences of the results need to be applied with caution.
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