Effects of aromatherapy on sleep quality in older adults: A meta-analysis

Abstract

Background:

Aromatherapy has been proposed as a complementary therapy to enhance sleep quality and regulate mood. However, few studies have specifically examined the efficacy of aromatherapy in managing sleep disorders in older adults. Therefore, the present study aims to systematically review the impact of aromatherapy on sleep quality among older adults.

Methods:

It employed a meta-analysis design. A systematic and comprehensive search was conducted across 7 databases to identify randomized controlled trials examining the effects of aromatherapy on sleep quality in older adults. Two researchers independently assessed the quality of the literature. The study adhered to the Preferred Reporting Items for Systematic Reviews and Meta-analysis checklist.

Results:

Aromatherapy demonstrated effectiveness in improving sleep quality among older adults (standardized mean difference [SMD] = −1.02; 95% confidence interval [CI] = −1.38 to −0.66; P < .001). Subgroup analyses based on aroma types, intervention modalities, and treatment durations revealed enhanced efficacy with lavender as the sole aroma (SMD = −1.39; 95% CI = −2.06 to −0.72; P < .001), non-inhaled aromatherapy (SMD = −1.73; 95% CI = −2.26 to −1.2; P < .001), and aromatherapy administered for less than 4 weeks (SMD = −1.16; 95% CI = −1.68 to −0.64; P < .001). Notably, significant effects of aromatherapy on anxiety (SMD = −0.83; 95% CI = −1.24 to −0.42; P < .001) and depression (SMD = −0.85; 95% CI = −1.30 to −0.39; P < .001) in older adults were also observed.

Conclusion:

This study indicates that aromatherapy improves sleep quality in older adults, with single-use lavender, non-inhalation aromatherapy, lasting less than 4 weeks being particularly effective. Aromatherapy also alleviates depression, but its effects on anxiety require further evaluation.

1. Introduction

1.1. Background

According to the data from China’s National Bureau of Statistics, as of the conclusion of 2020, the elderly population in China, aged 60 and above, had reached 265 million, constituting 18.7% of the total population. With the anticipated further rise in the proportion of the elderly population, concerns regarding the health issues of this demographic are expected to proliferate. Sleep disorders, a common ailment among the elderly, exhibit a prevalence of 46% within the Chinese elderly population, as reported in a study.^[1] The repercussions of sleep problems on health are multifaceted, encompassing adverse effects on the cardiovascular system, immune system, and mental well-being.^[2] Insufficient sleep is also linked to negative emotions such as anxiety and depression.^[2] Moreover, the quality of sleep correlates with overall quality of life and memory function.^[3,4]

Research has demonstrated that aromatherapy, employed as an adjunctive therapy, exerts a positive influence on enhancing sleep quality and regulating mood.^[5] Despite the widespread utilization of aromatherapy, both domestically and internationally, for improving sleep quality and addressing insomnia, there is a paucity of studies specifically investigating aromatherapy’s efficacy in addressing sleep disorders in the elderly. Consequently, this study conducts a meta-analysis, systematically examining literature data from both domestic and international sources, to assess the impact of aromatherapy on sleep quality in older adults. The findings aim to serve as a foundation for informed clinical practices.

1.2. Aims

This study evaluated the efficacy of aromatherapy in improving sleep quality among older adults. Our objectives were to determine whether aromatherapy enhances sleep quality and to identify the most effective types of aromatherapy interventions. Additionally, we assessed the impact of aromatherapy on anxiety and depression in this population.

2. Materials and methods

2.1. Inclusion and exclusion criteria

2.1.1. Inclusion criteria

The participants in this study comprised individuals aged 60 years and above who were afflicted with sleep disorders, and there were no restrictions regarding the gender of the participants; various forms of aromatherapy were administered to the experimental group as interventions, while the control group received routine care measures or no intervention; the primary outcome measure was the sleep quality of the patients, assessed through instruments such as the Pittsburgh Sleep Quality Index questionnaire. Secondary outcome measures included anxiety and depression, gauged using tools such as the Self-Rating Anxiety Scale; the study design employed was either a randomized controlled trial or a semi-randomized controlled trial, with no language restrictions.

2.1.2. Exclusion criteria

Studies of other interventions combined with aromatherapy; detailed experimental data from the study were not available; full text not available; Master’s and doctoral dissertations.

2.2. Search strategy

Computerized search databases encompassed China National Knowledge Infrastructure (CNKI), Wanfang Data, China Biology Medicine Disc, PubMed, Web of Science, Embase, and Cochrane Library. The search period extended from the inception of the database to September 8, 2023. The search terms included “Aromatherapy OR Aromatherapies OR Aroma Therapy OR Aroma Therapies OR Therapies, Aroma OR Therapy, Aroma” AND “Sleep quality OR sleep insomnia OR sleep problems OR sleep disorder OR sleep complaints OR sleep disturbance.” The search strategy employed a combination of subject terms and free words, tailored to the search protocols of individual databases. Simultaneously, references of the incorporated studies were scrutinized, and a manual search was conducted for studies meeting the inclusion criteria. This study was registered with International prospective register of systematic reviews (PROSPERO) under the registration number CRD420234718878.

2.3. Literature screening and data extraction

Initially, the gathered literature underwent deduplication using NoteExpress. Subsequently, the titles were reviewed for an initial screening of relevant studies. Following this, the abstracts were examined to exclude studies that did not meet the predetermined criteria. Finally, a thorough review of the full texts was conducted to identify literature aligning with the inclusion criteria. This process was carried out independently and cross-verified by 2 researchers, with consultation of relevant experts in the event of disagreements. The data extraction encompassed: basic information pertaining to the included studies; the number of cases, interventions, and intervention duration for the study subjects; the types of outcome indicators; experimental results data; indicators relevant to the assessment of literature quality.

2.4. Literature quality assessment

The quality of the literature was evaluated using the handbook for evaluating interventional studies provided by Cochrane Handbook 5.1.0 in terms of 7 indicators. The risk of bias of the included studies was independently evaluated by 2 investigators and the results were cross-checked.

2.5. Statistical methods

Due to the use of different scales to measure outcomes, sleep quality scores were normalized before conducting the meta-analysis. Revman 5.4 and Rstudio were used to perform meta-analysis of data from all included studies. χ² test and I² index were adopted to analyze the heterogeneity of the included studies; if P > .1 and I² < 50%, it indicated that there was homogeneity among studies, and the fixed effect model was selected for the analysis; if P < .1and I² ≥ 50%, it indicated that there was heterogeneity among studies; the source of heterogeneity was analyzed and the fixed effect model was applied for the analysis after exclusion by sensitivity analysis; if the heterogeneity still existed after exclusion, it was analyzed with random-effects model. Measurements were expressed as mean differences and 95% confidence intervals (CIs).

3. Results

3.1. Literature search results

The literature search process is visually depicted in Figure 1. The search strategy across various databases yielded a total of 989 pieces of literature in the initial search, reduced to 509 after deduplication. Following a preliminary review of titles and abstracts, 411 pieces of literature were excluded, and 98 were deemed relevant. Upon a more detailed examination of the full texts, 57 pieces of literature were excluded due to non-conforming intervention types, and an additional 24 did not meet the specified endpoint indicators. Five pieces of literature were unavailable for research data. Despite an effort to trace references, no compatible studies were identified. Consequently, a total of 10 studies,^[6–15] involving 692 patients, were ultimately included.

Figure 1.

The flow diagram of the selection procedure. CBM = China Biology Medicine Disc, CNKI = China National Knowledge Infrastructure.

3.2. Characteristics of included literature

The basic characteristics of the included studies are shown in Table 1, and the characteristics of the literature are summarized according to the table as follows. The countries of origin encompass China (7 studies), Korea (1 study), Turkey (1 study), and Iran (1 study), with the studies conducted between 2016 and 2022. The majority of the studies adopted a 2-armed randomized controlled trial design, except for 1 study, which employed a 3-armed structure involving an inhalation group, a massage group, and a blank control group. Experiment sample sizes ranged from 18 to 46.

Table 1.

Characteristics of included literature.

Study (year, country)	Participants	Number of subjects		Aroma types	Intervention types	Duration	Cognition tool
		Aromatherapy	Control
She[12] (2017, China)	Geriatric inpatients	40	40	Lavender, sweet orange, bergamot	Inhalation	2 wk	①③
Li[11] (2016, China)	Elderly people in the community	Group 1: 18 Group 2: 18	20	Lavender, sweet orange, bergamot	Group 1: inhalation Group 2: massage	2 wk	②
Zheng[15] (2020, China)	Neurology elderly patients	35	35	Lavender, sweet orange, bergamot	Inhalation	2 wk	①
Feng[7] (2023, China)	Institutionalized elderly	46	45	Chinese medicine sachet	Inhalation	8 wk	②
Xie[13] (2017, China)	Elderly people	20	20	Lavender, chamomile	Massage	8 wk	②
Hao[10] (2019, China)	Elderly lymphoma patients	41	41	Lavender	Inhalation	Unknown	②
Zhang[14] (2022, China)	Geriatric inpatients	44	44	Lavender	Inhalation	2 wk	②④⑤
Genç[8] (2020, Turkey)	Institutionalized elderly	30	29	Lavender	Inhalation	1 mo	②
Chun[6] (2017, Korea)	Elderly women living at home	32	30	Marjoram, orange	Inhalation	4 wk	⑥⑦⑧
Givi[9] (2019, Iran)	Elderly patients	32	32	Lavender	Inhalation	1 wk	②

①SRSS; ②PSQI; ③HAD; ④SAS; ⑤GDS; ⑥Korea sleep scale A; ⑦CES-D; ⑧State trait anxiety inventory-Y.

CES-D = the Center for Epidemiologic Studies Depression Scale, GDS = Geriatric Depression Scale, HAD = Hospital Anxiety and Depression Scale, PSQI = Pittsburgh Sleep Quality Index, SAS = Self-Rating Anxiety Scale, SRSS = Self-Rating Scale of Sleep.

Concerning subjects and interventions, one study exclusively involved female participants, while the others included both male and female subjects. Four studies employed single aromatherapy, and the remaining 6 utilized complex aromatherapies. Eight studies incorporated aromatherapy with lavender and 4 employed aromatherapy with sweet orange. Nine studies applied inhalation aromatherapy, wherein 4 placed the aromatic substance on the pillow, and 2 aerosolized aromatic oils for inhalation. Two studies employed massage aromatherapy, targeting the palms, wrists, arms, neck, and shoulders.

The intervention duration across the included studies ranged from 1 to 8 weeks, with the majority intervening for 2 to 8 weeks.

Regarding sleep quality indicators, 7 studies employed the Pittsburgh Sleep Quality Index, 2 utilized the Self-Rating Scale of Sleep (SRSS), and 1 employed the Korea Sleep Scale A.

3.3. Quality assessment of literature

The results of the literature quality assessment are shown in Figure 2.The quality of the 10 included studies was B. Only 2 studies blinded the implementer, 1 of which blinded both the implementer and the patient, and the others did not; 5 studies reported the method of generating the randomized order, 4 of which used randomized numeric tables and 1 computerized randomization. The risk of data completeness was low in all studies except 1, which did not report experimental data completeness; all studies had a low risk of selective reporting.

Figure 2.

The risk for the bias of included 10 studies.

3.4. Effect of aromatherapy on sleep quality

All studies included in the analysis consistently reported a positive impact of aromatherapy on sleep quality among older adults, demonstrating an enhancement in sleep quality compared to the control group. Combining and analyzing data from 10 studies involving a total of 674 participants, a random-effects model was employed due to notable heterogeneity. The pooled results revealed a statistically significant influence of aromatherapy on the sleep quality of older adults in comparison to the control group (SMD = −1.02; 95% CI = −1.38 to −0.66; P < .001; I² = 79%) (Fig. 3). Notably, the combined results exhibited substantial heterogeneity, and a sensitivity analysis, excluding one study,^[14] was conducted. The exclusion was based on its failure to report a specific intervention duration. Upon re-pooling the results, a similar outcome was observed, with a reduction in heterogeneity (SMD = −0.83; 95% CI = −1.05 to −0.61; P < .001; I² = 39%).

Figure 3.

Forest plot of the total effects of aromatherapy on sleep quality. CI = confidence interval, IV = inverse-variance weighting, SD = standard deviation.

3.5. Effects of aromatherapy on anxiety

Three studies^[6,12,14] investigated the impact of aromatherapy on anxiety, amalgamating data from a total of 230 individuals. The data, subjected to analysis through a random-effects model due to substantial heterogeneity, yielded pooled results indicating a beneficial effect of aromatherapy on anxiety levels (SMD = −0.83; 95% CI = −1.24 to −0.42; P < .001; I² = 56%) (Fig. 4). Following a sensitivity analysis that excluded one study,^[14] the combined effect size experienced a reduction (SMD = −0.62; 95% CI = −0.96 to −0.28; P < .001, I² = 0%), with statistical significance remaining unaltered.

Figure 4.

Forest plot of the total effects of aromatherapy on anxiety. CI = confidence interval, IV = inverse-variance weighting, SD = standard deviation.

3.6. Effects of aromatherapy on depression

Three studies^[6,12,14] investigated the impact of aromatherapy on depression, and the aggregated data from a total of 230 individuals indicated a beneficial effect of aromatherapy on depression (SMD = −0.85; 95% CI = −1.30 to −0.39; P < .001; I² = 64%) (Fig. 5). Following a sensitivity analysis that excluded one study,^[14] the combined effect size experienced a reduction (SMD = −0.61; 95% CI = −0.95 to −0.28; P < .001, I² = 0%).

Figure 5.

Forest plot of the total effects of aromatherapy on depression. CI = confidence interval, IV = inverse-variance weighting, SD = standard deviation.

3.7. Subgroup analysis

Given the notable heterogeneity observed among studies, we employed grouping and subgrouping based on the type of aromatherapy intervention (inhalation, non-inhalation), type of aromatics (single, mixed), and duration of treatment (≤4, >4 weeks). The corresponding results of these analyses are presented in Table 2. For non-inhalation aromatherapy, the effect size was −1.73 (95% CI = −2.26 to −1.20), while for inhaled aromatherapy, the effect size was −0.97 (95% CI = −1.35 to −0.59), indicating a superior impact on sleep quality for patients receiving inhaled aromatherapy. In the context of aromatics, the effect size for single aromatherapy was −1.39 (95% CI = −2.06 to −0.72), in contrast to mixed aromatherapy with an effect size of −0.73 (95% CI = −1.03 to −0.44), suggesting improved sleep quality for patients subjected to single aromatherapy. Furthermore, enhanced sleep quality was associated with an effect size of −1.16 (95% CI = −1.68 to −0.64) for intervention periods >4 weeks, as compared to −0.89 (95% CI = −1.44 to −0.34) for intervention periods ≤4 weeks.

Table 2.

Differences in sleep quality across subgroups.

Subgroup	No. of studies	Participants	SMD (95% CI)	P value	I 2
Aroma types
Single	4	293	−1.39 (−2.06 to −0.72)	<.001	85%
Mixed	6	381	−0.73 (−1.03 to −0.44)	<.001	47%
Intervention types
Inhalation	9	633	−0.97 (−1.35 to −0.59)	<.001	80%
Massage	2	78	−1.73 (−2.26 to −1.20)	<.001	0%
Duration
≤4 wk	7	169	−1.16 (−1.68 to −0.64)	<.001	84%
>4 wk	3	425	−0.89 (−1.44 to −0.34)	<.001	62%

CI = confidence interval, SMD = standardized mean difference.

3.8. Publication bias

The potential presence of publication bias was assessed through visual examination utilizing a funnel plot and the Egger test. Upon visual inspection, the funnel plot exhibited a degree of symmetry (Fig. 6). The Egger test, with a P value of .127 (P > .05), indicated no statistically significant publication bias (Fig. 7).

Figure 6.

Funnel plot.SE = standard error, SMD = standardized mean difference.

Figure 7.

Graph of the Egger test.

4. Discussion

4.1. Effect of aromatherapy on sleep quality

This study suggests that aromatherapy improves sleep quality in older adults, aligning with the outcomes of prior research on the sleep-improving effects of aromatherapy.^[16] The mechanism may be related to the fact that aromatic substances promote the release of gamma-aminobutyric acid by affecting the nervous system.^[17,18] Previous studies have also confirmed the positive effects of aromatherapy in different populations, including intensive care unit patients,^[19] chemotherapy patients,^[20] menopausal women,^[21] operating room personnel,^[22] and postpartum women.^[23] This article conducts a subgroup analysis of aromatic. However, studies in the elderly are limited. The results of the present study emphasize the efficacy of aromatherapy in improving the quality of sleep, especially among the elderly. Aromatherapy is an effective non-pharmacological intervention that does not involve the risks associated with traditional sleep medications, compared to sleeping medicines that often have adverse side effects.^[24,25] It is foreseeable that it will receive more attention as an adjunctive treatment for insomnia in the older adults due to the limitation of medical resources.

Substance types acknowledge limitations due to some literature utilizing multiple aromatic substances simultaneously. Consequently, the analysis exclusively scrutinizes the effects of either a single aromatic substance (lavender) or a combination of aromatic substances. The results reveal that the sole application of lavender proves more effective in enhancing sleep quality among older adults, aligning with the findings of Cheong et al.^[26] Nevertheless, further research is imperative to ascertain whether the exclusive use of lavender surpasses other individual aromatics. In the realm of aromatherapeutic modalities, subgroup analyses indicate that non-inhalation aromatherapy potentially exerts a more favorable impact on improving sleep quality in older adults, consistent with the conclusions drawn by Her and Cho.^[27] However, the reliability of these results remains modest due to the limited inclusion of non-inhalation aromatherapy in only 2 studies. Within the subgroup analysis of the intervention period, both subgroups yield favorable outcomes, with the intervention period of ≤4 weeks demonstrating superior results. However, a notable degree of heterogeneity exists in both subgroups, likely attributed to variations in intervention methods and classes of aromatics. Although the overall effectiveness of aromatherapy is recognizable, subgroup analyses are necessary to determine the differential effects of the type of aromatherapy intervention, the type of aromatic substance, and the duration of the intervention on sleep quality in older adults. By combining this information with patient specifics and preferences, an optimal aromatherapy program can be developed for older adults.

4.2. Effects of aromatherapy on anxiety

Three studies investigated the effects of aromatherapy on anxiety in older adults, and the combined effect sizes suggest that aromatherapy can improve anxiety in older adults. The aroma of essential oils in aromatherapy can stimulate the emotional center of the brain through the olfactory system, and the hypothalamus releases neurotransmitters such as endorphins and enkephalins after stimulation, which can regulate the emotional and psychological state, reduce anxiety and stress, and make people feel relaxed and happy.^[28] The results of existing systematic reviews have shown that aromatherapy can reduce anxiety in cancer patients,^[29] anxiety during labor in primiparous women,^[30] menopausal anxiety,^[31] and anxiety in hemodialysis patients.^[32] However, considering that only 3 studies were included in the effect of aromatherapy on anxiety and there was a large heterogeneity among them, the source of heterogeneity could not be identified after sensitivity analysis. Therefore, the combined effect size results should be treated with caution, and the role of aromatherapy on anxiety in older adults still needs to be supported by more studies.

4.3. Effects of aromatherapy on depression

Regarding the amelioration of depression among older adults, the results of 3 studies were synthesized, revealing that aromatherapy effectively alleviates depressive symptoms in this demographic. Notably, a 2018 study highlighted a 35% detection rate of depressive symptoms among the elderly in China, with a discernible increase in prevalence with advancing age.^[33] The burden of depressive symptoms not only inflicts substantial distress upon elderly individuals but also exerts a profound impact on the well-being of their families. Given the escalating proportion of elderly individuals, there is an imperative need for heightened awareness and attention to the implications of depression in this population. Traditionally, depression treatment predominantly relies on medication, yet antidepressants may entail adverse effects such as headaches and nausea. Prior research underscores the efficacy of aromatherapy in mitigating depressive symptoms.^[34] In comparison to medication, aromatherapy emerges as a cost-effective and notably safe adjunctive treatment.

5. Limitations

This study exhibits certain limitations. Despite the inclusive approach in searching for literature across various languages, the final set of included studies predominantly originated from China, with only one piece of literature representing each of the other countries (Turkey, South Korea, and Iran). This limited diversity in the sample countries, particularly the singular representation from non-Chinese nations, poses a potential constraint on the generalizability of the study’s results. Moreover, all the studies encompassed small-sample sizes and adopted a single-center design, contributing to an overall moderate quality rating for the literature. The reliance on such study characteristics may impact the reliability of the results, warranting cautious interpretation.

6. Conclusions

Based on the findings, aromatherapy demonstrates efficacy in enhancing sleep quality in older adults while alleviating symptoms of anxiety and depression. However, concerning anxiety improvement, despite the observed significant intervention effect, notable heterogeneity among the 3 studies indicates the necessity for further research to substantiate the impact of aromatherapy on anxiety conditions.

Author contributions

Software: Kun Xu, Quanyue Ji.

Writing – original draft: Kun Xu, Shouyan Wang, Yan Ni, Tianyun Liu.

Methodology: Quanyue Ji.

Project administration: Tianyun Liu.

Writing – review & editing: Kun Xu.