Drugs such as sedative-hypnotics and antidepressants are widely used in clinical interventions for sleep disorders.7 Despite the immediate effects of sedative-hypnotics, the various side-effects associated with their use, such as drug tolerance, dependence, misuse, and decreased cognitive function,6, 7, 8 lead to non-pharmaceutical treatments being preferred as first-line therapy for individuals with chronic insomnia.9 These may include complementary and alternative therapy such as cognitive-behavioral therapy,10 meditation,11 music therapy,12 and aromatherapy.13
However, despite these efforts, the problem of sleep disorders is serious. In America, the prevalence of sleep problems in working adults significantly increased from 30.9 % in 2010 to 35.6 % in 2018.14 Sleep problems commonly occurred in people, in their 50 s, who worked in specific fields. To meet the demands of these people the sleep industry has grown over the years.15,16 The U.S. sleep industry has been growing more than 8 % annually, and China's sleep industry has been growing at an annual rate of 24 % since 2010.17, 18, 19 The sleep industry includes manufacturing of products such as special mattress and pillows, IT products, and sleep-inducing foods, and aromatherapy.15
Aromatherapy is a complementary alternative therapy that can be applied on its own due to its simple application. Its several advantages for reducing stress and improving sleep quality include low cost, ease of access, lesser time and space constraints, and quick effects.11,20, 21, 22, 23, 24 Aromatherapy is performed by inhaling, massaging, and bathing in essential oils extracted from aromatic plants. The aromatic molecules enter the human body through the respiratory tract and skin; they affect the limbic system by adjusting and transforming the messages passing through the hypothalamus.24, 25, 26, 27 Aromatherapy has been shown to affect physical, mental, and psychological factors in a wide range of participants by reducing sympathetic activity, increasing parasympathetic nerve activity, relieving stress, enabling muscle relaxation, and improving sleep quality.28, 29, 30
In aromatherapy for sleep, the focus was on aiding relaxation and stabilizing the mind and body for deep sleep.24,26 Aroma essential oils for sleep include lavender,31 rosa damascene,32 and marjoram.33 To date, many studies conducted on the effect of aromatherapy on sleep quality have shown improvement in diverse participants34, 35, 36, 37, 38, 39, 40, 41 including students,37 adults (specifically women),28,42,43 elderly people,34,44 and cancer and type 2 diabetic patients,45,46 and meta-analyses have aimed to generalize the effects of aromatherapy on sleep.13,47,48
In a study by Lin et al47, aromatherapy using both single and blended oils, and performed through inhalation, non-inhalation, and mixed methods was shown to be effective in improving sleep. Furthermore, in study by Kim et al,13 it has been shown that both the inhalation and massage methods are effective in improving sleep, irrespective of the type of oil used (single or blended); however, the massage method is more effective than the inhalation method. Additionally, Kim et al13 have reported statistically significant differences in effect size between the inhalation, oral intake, and massage methods for aromatherapy, indicating that the effect of aromatherapy varies depending on the application method. Notably, both studies did not analyze the duration and frequency of inhalations required for the efficacy of aromatherapy. Moreover, to date, no meta-analyses have focused on generalizing the application of aromatherapy for sleep. However, considering the increasing use of aromatherapy to improve sleep quality, studies are needed to verify the effectiveness of aromatherapy and to analyze its method of application in order to standardize safe and effective use of aromatherapy.27
Therefore, a study with combined effect analysis of aromatherapy factors (e.g., session time, duration, and frequency of intervention, and method of aromatherapy application) is required to ensure safe and effective use of aromatherapy. Furthermore, presenting the combined effects of aromatherapy application methods is necessary to standardize the aromatherapy protocol for use as a nursing intervention to improve sleep quality.
This systematic review and meta-analysis aimed to identify the quantifiable effects of aromatherapy on the sleep quality of adults and elderly people and the combined effects of aromatherapy on sleep, while providing relevant data for the utilization of aromatherapy as a nursing intervention to improve sleep quality. Furthermore, a sub-analysis of the improvement in sleep quality was conducted to determine the variation in the effects of aromatherapy depending on the program’s characteristics, and to provide evidence for the development and application of an integrated aromatherapy program that may be recommended as a standard aromatherapy protocol, suitable for Korean adults and elderly people.
