The Effect of Aromatherapy on Post-Exercise Hypotension: A Pilot Study

Abstract

The global prevalence of hypertension continues to rise, affecting an estimated one billion worldwide. Regular exercise is well recognized as a non-pharmacological approach for individuals with hypertension due to its blood pressure (BP)-lowering effect, largely attributed to repeated exposure to post-exercise hypotension (PEH). Recent evidence also indicates that aromatherapy can contribute to BP reduction, indicating that combining aromatherapy with exercise may enhance the overall BP-lowering effects. Therefore, this pilot study aimed to investigate the effects of aromatherapy on PEH during the recovery phase following exercise. Fourteen healthy young males (22.7 ± 0.7 yrs) participated in this randomized crossover-designed study. All participants completed two exercise sessions per week, each lasting 30 min, at a target heart rate (HR) of 60–65%. The individuals inhaled either aroma oil or water vapor at 5, 35, 65, and 95 min after exercise. The HR, BP, blood lactate level, and arterial stiffness index were measured before and after the exercise. Our findings revealed the following. (1) PEH occurred in both groups. (2) In the aroma group, PEH was augmented compared with the control group, with the maximum reduction in BP being greater in the aroma group. (3) The reduction in arterial stiffness was greater and longer in the aroma group than in the control group. (4) The changes in the lactate levels after exercise did not differ between the groups. Our findings indicate that aromatherapy can amplify PEH, suggesting that its use after exercise may help maximize the positive effects of exercise on BP reduction.

1. Introduction

Hypertension, defined as persistently elevated blood pressure (BP), is a major global health concern that contributes significantly to the burden of cardiovascular diseases [1]. The global population with hypertension is steadily increasing, exceeding one billion individuals; thus, hypertension has become a critical public health challenge [2]. According to the United States Centers for Disease Control and Prevention [3], the prevalence of hypertension among adults aged 18 and older was 47.7% between August 2021 and August 2023. Furthermore, accumulated data have demonstrated that the prevalence of hypertension in young individuals is increasing [4]. It was reported that the prevalence of hypertension among adults aged 18–39 years is 30.0% in men and 16.4% in women [3]. Munter et al. suggested that this increase can be attributed to unhealthy lifestyle habits and the obesity epidemic [5].

Regular exercise is the most effective non-pharmacological approach to managing BP [6]. Post-exercise hypotension (PEH) refers to a temporary reduction in BP below resting levels that occurs during the recovery period following acute exercise. Particularly for hypertensive individuals, the cumulative effects of repeated PEH induced by regular exercise, referred to as training effects, can eventually lead to sustained reductions in BP [7]. Studies have demonstrated that PEH lasts 10–170 min after 20–60 min of exercise, depending on the type, length, and intensity of the physical activity [8]. Specifically, aerobic exercise elicits a greater PEH effect than resistance exercise [9]. Moreover, moderate-intensity aerobic exercise at 60% maximum oxygen consumption (VO₂max) induces a more pronounced PEH response than low-intensity aerobic exercise at 40% VO₂max [9].

Aromatherapy, which involves the use of aromatic plant extracts for therapeutic purposes, has gained traction as a complementary approach to improve various aspects of health, particularly cardiovascular responses such as BP and heart rate (HR), through the inhalation of essential oil fragrances [10]. Aromatherapy for patients with hypertension has been demonstrated to reduce BP and stress [11], as well as blood epinephrine and cortisol levels [12]. The mechanism underlying these effects involves the absorption of inhaled aroma oil particles by the olfactory nerve cells through the cilia located on the ceiling of the nasal cavity. These stimulations can be transmitted to the brain through the limbic system of the cerebrum. From the limbic system, the signals are relayed to the hypothalamus, which then communicates with the autonomic nervous system (ANS) and pituitary gland to regulate hormones [13]. Consequently, the aromatherapy-induced reduction in sympathetic nerve activity (SNA) and increase in parasympathetic nerve activity (PNA) can impact BP [14]. Activation of the limbic system with essential oil inhalation may also increase dopamine release, which is associated with pleasure and relaxation, thereby affecting BP [15]. Moreover, studies have suggested that aromatherapy can assist in the treatment of physical ailments by modulating the endocrine and immune systems and directly affects vascular function [16,17].

Given the previous studies demonstrating that aromatherapy alleviates BP, it can be speculated that aromatherapy can further enhance PEH, potentially influencing the magnitude and duration of the condition. However, the effect of aromatherapy on BP during the post-exercise period remains unexplored. Therefore, as a pilot study, we hypothesized that aromatherapy following exercise exaggerates the PEH response. The purpose of this study was not only to expand our understanding of the physiological effects of aromatherapy on BP but also to provide preliminary evidence for novel and integrative approaches to enhance the post-exercise reduction in BP. The results of this pilot study could guide future strategies for enhancing the BP-lowering effects of exercise and offer insightful advice to individuals who want to maximize their health outcomes in response to physical activity.

2. Materials and Methods

2.1. Participants

The minimum number of participants (n = 12) for this pilot investigation was calculated to detect a treatment difference with a power of 0.8, a significance level of 0.05, and an effect size of 0.7 for the crossover study design using G*Power software (version 3.1.9.7) [18]. Considering the 20% withdrawal, 14 healthy male volunteers (22.7 ± 0.7 years old) were recruited, with all individuals participating in two experiments. The eligibility criteria were as follows: ① no history of cardiovascular, musculoskeletal, or neurological disorders; ② no use of aromatherapy in the past 3 months; ③ not currently taking any medications that influence BP; and ④ no diagnosis of rhinitis, asthma, or respiratory diseases that limit inhalation. Before participating in the study, all individuals were informed of the potential risks and discomfort and provided written informed consent.

2.2. Experimental Protocol

This study employed a randomized crossover design. The participants visited the laboratory twice, with a one-week wash-out interval between the visits. This washout period was chosen based on the short-acting nature, rapid clearance of essential oil constituents, and precedents in a previous crossover study [19], which was complemented by a trial using a shorter washout interval (2 days) while assuming no carryover effects [20]. It was also considered with a study showing that physiological responses to acute exercise return to baseline within 24–72 h in healthy individuals [21]. The individuals were instructed to fast overnight but were allowed to drink water before each visit. The participants were also instructed to avoid excessive physical activity, alcohol, nicotine, and caffeine for 24 h before each laboratory visit. To ensure laboratory standardization, the room temperature and humidity were maintained at 20–25 °C and 40–60%, respectively.

The experimental procedure is illustrated in Figure 1. Briefly, upon arrival at the laboratory at 10:00 a.m., anthropometric measurements were obtained using a digital height- and weight-measuring machine (DS-103M, Dong-Sahn JENIX Co., Seoul, Republic of Korea). The body composition was determined using bioelectrical impedance analysis (Inbody 720, Biospace Co., Seoul, Republic of Korea), which is widely used to estimate body fat percentage, fat mass, and fat-free mass [22]. After baseline resting HR, BP, blood lactate (BL), and arterial stiffness index (ASI) measurements, the participants rested on a medical couch for 10 min. Subsequently, the participants performed 30 min of treadmill running at a 0% incline, which included a 5-min warm-up followed by 25 min of main exercise at 60–65% of their age-predicted maximal HRs. The HR during exercise was monitored using a sensor (Polar H10, Polar, Kempele, Finland). After exercise, the participants were seated immediately and remained at rest on a medical couch in the laboratory for 120 min with food and drink restrictions. The participants inhaled either aroma oil or water vapor at 5, 35, 65, and 95 min following exercise. This timing and frequency were determined based on previous studies that investigated the effects of exposure to external physiological stimulation on PEH [23,24].

The BP, HR, and ASI were assessed at 0, 10, 20, 30, 60, 90, and 120 min, with BL concentrations measured at 0, 15, 30, and 60 min after exercise. The HR and BP were measured in the left arm using a digital BP machine (HBP-1320, Omron, Kyoto, Japan). Measurements were acquired twice at 1-min intervals, and the average of the two readings was used for analysis. The BL levels were assessed using a small amount of blood collected from the fingertips of the right hand using a lactate analyzer (Lactate Pro 2, Kyoto, Japan).

The ASI was measured in the left arm using the second derivative of the photoplethysmogram (SDPTG) via photoplethysmography (uBioClip v70, Biosense Creative Co., Seoul, Republic of Korea) as previously described [24]. Briefly, a sensor was noninvasively placed on the tip of the index finger to record the pulse wave in a capillary vessel for 1 min. SDPTG facilitates the analysis of wave indices, including the b/a ratio, which can be utilized to identify increased arterial stiffness [25]. All measurements were performed by the same investigator (S.P.).

2.3. Aroma Inhalation

In this study, Ylang-Ylang (Cananga odorata) aroma oil was provided by Plant Fragrance Technology (Seoul, Republic of Korea). Ylang-Ylang essential oil is widely employed in aromatherapy and has been reported to promote psychological relaxation and suppress sympathetic nervous system activity, thereby potentially assisting in stress reduction and BP regulation [26,27]. Notably, key active compounds, such as linalool (13.6%) and benzyl acetate (25.1%), possess sedative and anti-inflammatory properties, which are relevant to the modulation of cardiovascular parameters and ANS responses examined in this study [27]. The essential oil is extracted from flowers via steam distillation [28] and is considered safe for inhalation, with promising clinical applicability [29]. Following established protocols, the intervention involved applying three drops of oil onto a gauze pad, which participants then inhaled from a distance of 10 cm for 3 min [30]. The bottle containing the aroma oil was stored at room temperature away from direct sunlight, and the gauze used after each inhalation was discarded and replaced with a fresh piece for each session.

2.4. Statistical Analysis

Values are presented as the mean ± standard error of the mean. The mean arterial pressure (MAP) was estimated using the formula MAP = (2/3 × diastolic blood pressure [DBP]) + (1/3 × systolic blood pressure [SBP]). A two-way repeated measures analysis of variance (ANOVA) with time and treatment as within-subject factors was conducted to assess the effects of time, treatment, and their interaction. If a significant effect was found, then the Holm–Sidak post hoc test, which is known to control the family-wise error rate, was conducted to examine which time points differed from a pre-exercise value or between treatments. All data were analyzed using SigmaPlot (version 12.5), and statistical significance was set at p < 0.05.

3. Results

The physical characteristics of the participants, which demonstrated no significant differences between treatments conducted 1 week apart, are presented in

Table 1. Physical characteristics of subjects (n = 14).

Variable	Mean ± SEM
Age (yrs)	22.7 ± 0.7
Weight (kg)	75.1 ± 2.0
Height (cm)	177.4 ± 1.5
BMI (kg·m−2)	23.8 ± 0.5
Body fat (%)	13.5 ± 1.4
Muscle mass (kg)	37.1 ± 0.9
Fat mass (kg)	10.3 ± 1.3
Resting HR (beats·min−1)	63.1 ± 1.8
Resting SBP (mmHg)	118.5 ± 1.4
Resting DBP (mmHg)	67.4 ± 1.5
Resting MAP (mmHg)	84.7 ± 1.4

BMI = body mass index; HR = heart rate; SBP = systolic blood pressure; DBP = diastolic blood pressure; MAP = mean arterial pressure; SEM = standard error of the mean. There is no difference in any of the characteristics between treatments, and the average of two measurements is denoted.

.

The HR changes (post-exercise minus pre-exercise) during the post-exercise recovery period are presented in Figure 2. We observed a significant interaction (F_{(7, 91)} = 602.37, p < 0.001, η²_p = 0.98) and time effect (F_{(7, 91)} = 3.85, p = 0.01, η²_p = 0.23). Post hoc analysis of the time revealed that the HR significantly increased at 0, 10, and 20 min after exercise in both groups compared with the pre-exercise HR. No significant group effect (p = 0.32) indicated that the changes in HR during the recovery period did not differ between the groups.

Figure 3 illustrates the changes in BP following exercise. We observed a significant interaction for SBP (F_{(7, 91)} = 7.06, p < 0.001, η²_p = 0.35) and MAP (F_{(7, 91)} = 5.36, p < 0.001, η²_p = 0.29) but not for DBP (p = 0.10). A significant time effect was found for SBP (F_{(7, 91)} = 67.90, p < 0.001, η²_p = 0.94), DBP (F_{(7, 91)} = 23.61, p < 0.001, η²_p = 0.60), and MAP (F_{(7, 91)} = 53.49, p < 0.001, η²_p = 0.84), demonstrating that PEH appeared. As a result of post hoc tests, the SBP significantly decreased at 20, 30, 60, and 90 min, and the MAP significantly decreased at 30, 60, and 90 min compared with the pre-exercise values in the control group. A significant treatment effect was found for SBP (F_{(1, 13)} = 15.42, p < 0.01, η²_p = 0.44) and MAP (F_{(1, 13)} = 5.72.61, p = 0.03, η²_p = 0.29), with the post hoc test results showing that the aroma group demonstrated significantly greater reductions in BP, particularly at the mid-to-late recovery time points (SBP at 20, 30, 60, and 90 min and MAP at 30, 60, and 90 min), compared with the control group. These results suggest that aroma inhalation during the recovery period after exercise enhanced PEH.

The changes in the ASI (b/a ratio) during the recovery period are displayed in Figure 4. A significant interaction (F_{(7, 91)} = 2.05, p = 0.04, η²_p = 0.17) was found along with a time (F_{(7, 91)} = 3.32, p = 0.03, η²_p = 0.25) and treatment effect (F_{(1, 13)} = 4.51, p = 0.03, η²_p = 0.31). Post hoc tests revealed that the ASI was significantly decreased only at 10 min after exercise compared with the pre-exercise values in the control group, while the ASI was significantly reduced at 0, 10, 20, and 30 min post-exercise compared with the pre-exercise values in the aroma group. The ASI changes after exercise significantly differed between the groups at 20 and 30 min, but this difference was less apparent during the later recovery period. This finding demonstrates that exercise can acutely mitigate arterial stiffness and that this effect can be augmented by aroma inhalation during the post-exercise recovery period.

The BL concentration was assessed as a marker of metabolic fatigue recovery following exercise (

Table 2. Blood lactate (mmol/L) measured before and after exercise.

Time (min)	CON	AROMA
At rest	3.0 ± 0.4	2.8 ± 0.3
0	7.4 ± 1.4 *	9.1 ± 1.7 *
15	4.7 ± 0.6 *	5.7 ± 1.1 *
30	4.1 ± 1.0	3.9 ± 0.7
60	3.4 ± 0.4	2.8 ± 0.2

CON = exposure to water vapor; AROMA = inhalation of aroma oil. * p < 0.05 compared with pre-exercise (at rest) values. There was no difference between treatments at any time point.

). No significant interaction was found (p = 0.09). The time effect was significant (F_{(4, 52)} = 7.37, p < 0.001, η²_p = 0.64), but the treatment effect was not (p = 0.46). As a result of post hoc testing, the BL concentrations significantly increased at 0 and 15 min post-exercise compared with pre-exercise in both groups; however, there was no difference between the groups.

4. Discussion

Given that both aromatherapy and exercise can reduce BP, this pilot study investigated whether aromatherapy has a synergistic effect on PEH. To the best of our knowledge, this is the first study to evaluate the impact of aromatherapy on PEH. Our findings indicate that aroma oil inhalation during the post-exercise recovery phase can enhance the BP-lowering effect of exercise.

Elevated BP is recognized as an independent risk factor for cardiovascular disease (CVD). Thus, preventing or reducing BP is a crucial medical objective to lower CVD-related mortality and complications in individuals with hypertension [2]. Among the strategies for the management of BP, exercise is well characterized and plays a pivotal role as a non-pharmacological approach. Previous studies have provided evidence that regular exercise can prevent or reduce resting BP, primarily through the cumulative effect of repeated transient BP reductions following acute exercise, known as PEH [6]. In our study, acute aerobic exercise at a moderate intensity for 30 min induced PEH, which began at 20 min and persisted through 90 min of recovery, consistent with previous studies demonstrating that exercise elicits PEH. However, the magnitude and duration of PEH vary across studies, likely due to differences in exercise type, length, and intensity. In addition, factors such as the sex, age, and disease status of participants may also contribute to these variations [8,31].

Olfactory stimuli from aromatherapy have been documented to influence cardiovascular variables. In particular, extensive research has focused on aromatherapy-induced changes in the ANS, resulting in decreased SNA and increased PNA. Moreover, aromatherapy has been demonstrated to enhance positive emotions and decrease negative emotional states, possibly via the dopaminergic reward system activation [15]. Olfactory nerves are believed to transmit information to primary olfactory regions, such as the amygdala, piriform cortex, and entorhinal cortex. In addition, olfactory input might be relayed to secondary olfactory regions, including the hippocampus, thalamus, insula, and orbitofrontal cortex [32]. Therefore, it is plausible that olfactory exposure to aromas could activate these brain regions, potentially modulating ANS activity and emotional responses [33]. Considering this, our finding that aroma inhalation augments PEH also implies that olfactory stimuli from aroma oil may modulate the ANS. Consequently, this neural change as well as dopaminergic activation via olfactory stimulation may lead to reduced vascular tone and decreased peripheral vascular resistance, ultimately amplifying the effects of exercise on PEH. This is in line with our finding that exercise-induced decreases in arterial stiffness are magnified and prolonged by aroma inhalation during the recovery phase after exercise. Unfortunately, we could not directly measure changes in SNA or PNA in this pilot study. Thus, a future investigation is warranted. A notable finding was the lack of difference in HR recovery in response to aromatherapy, despite the potential influence of aroma on ANS and thereby on the HR. Similar results have been reported in the literature. A recent study discovered no difference in HR recovery between lavender and placebo treatments at 5, 10, and 15 min during the recovery phase after exercise [34]. In addition, Romine et al. also reported that exposure to lavender following exercise has no significant effect on HR recovery [35]. Unfortunately, these previous studies did not discuss these findings, and we could not find clues to draw a putative explanation for this finding. Thus, this part remains an interesting topic for future research, with a large sample size and different dosages, delivery methods, exercise modalities, etc. Lactate is produced from carbohydrate glycolysis under anaerobic conditions, and its accumulation leads to acidosis, which contributes to fatigue [12]. Thus, rapid lactate clearance is essential for quick recovery after exercise. In this pilot study, post-exercise aromatherapy did not seem to influence lactate clearance, implying that aromatherapy-induced augmentation of PEH might not be associated with metabolic effects. Although subtle evidence suggests that aromatherapy can influence the hormonal balance by stimulating the hypothalamus and pituitary glands [28,35], the relatively small dosage and brief exposure time in this study may not significantly impact metabolic recovery.

This pilot study has several limitations, particularly in its methodological approaches, to notice. First, since the study involved only young normotensive males, generalizing the results to older individuals, patients with hypertension, or even females remains uncertain [36]. Nonetheless, given the global trend of increasing prevalence of hypertension among younger populations, our results are somewhat meaningful and indicate the necessity of application to larger and more diverse populations. Second, a one-week washout interval between experiments might not be enough to completely avoid the carryover effects. Although previous studies on the effect of essential oils exhibited that a washout period of one week or even less than a week did not influence their results [19,20], this would be different depending on the essential oil types, exposure methods, duration, timing, etc. Therefore, a longer interval needs to be considered for solid outcomes in future studies. Third, blindness to treatments might be unsecure due to the unique odor of essential oils, although the participants were not informed about inhaling materials. Thus, it is required to consider ways to address this issue in future research.

Overall, our preliminary findings from this pilot study can lead to the future studies which conduct experiments to ensure clinical efficacy in large participant groups or different groups of subjects, such as hypertensives and elderlies, who need urgent help to control their BP. Future studies should explore different aromas and their comparative effects on cardiovascular and autonomic parameters with mechanistic biomarkers and autonomic measures. In addition, as long-term interventions are required to alter physiological baselines, the acute effects observed in this study limit the conclusions regarding the long-term benefits or habituation effects of exercise on BP and vascular stiffness.

5. Conclusions

This pilot study is the first to investigate the effect of post-exercise aromatherapy on PEH. The results of this study provide preliminary evidence that aromatherapy may facilitate BP reduction induced by exercise along with both a prolonged magnitude and duration of the transient decrease in arterial stiffness during the recovery phase after exercise. Given the minimal side effects and ease of implementation, aromatherapy can be considered a viable adjunct in recovery protocols for young healthy individuals, such as athletes and habitual exercisers, and as a non-pharmacological approach along with exercise for controlling BP.