Correlation Study on the Autonomic Nervous System Balance Using HRV According to Preference for Spicy Taste

Article information

J Korean Med. 2024;45(4):33-44

Publication date (electronic) : 2024 December 1

doi : https://doi.org/10.13048/jkm.24055

Tae Yang Kwon¹, Seung Woo Im², Jin Suk Koo^3,

¹Department of Bioresource Sciences, Andong National Univ

²Korean Medicine-Application Center, Korea Institute of Oriental Medicine

³Department of Forest Science, Andong National Univ

Correspondence to: Jin Suk Koo, Department of Forest Science, Andong National Univ, Andong, 36729, Republic of Korea, Tel: +82-54-820-5845, Fax: +82-54-820-6252, E-mail: kimkoo1114@anu.ac.kr

Received 2024 September 24; Revised 2024 November 7; Accepted 2024 November 21.

Abstract

Introduction

Spicy taste is becoming popular not just in South Korea but around the world. Restaurants that specialize in spicy foods have become hugely successful and street foods as well as common snacks found in convenience stores have released a ‘spicy’ version, to meet the demand of the consumers that are seeking out spicy taste¹⁾. According to a study by Choi²⁾, 40.3% of office workers in Seoul have responded that they prefer spicy taste the most, for reasons such as stress relief and addictive nature. However, focusing on spicy foods for food intake may increase the risk of gastric cancer or induce cognitive decline in the elderly due to neurotoxicity - thus, it is advisable to take a diverse group of foods for health^3,4).

In spicy foods, high and low temperatures are felt as pain through the TRPV1 (transient receptor potential vanilloid 1) and TRPA1 (transient receptor potential ankyrin 1) in the TRP (transient receptor potential) channels, which becomes the origin of the spicy taste. Spicy taste is felt as hot pain and is induced by the TRPV1 when hot pepper and pepper is ingested, or as cold pain by TRPA1 when horseradish, cinnamon or mint is ingested^5,6). The pain from TRPV1 generates dopamine, which leads to addiction and itchiness⁷⁾.

There are reports that people prefer spicy foods and tend to have poor dietary habits with imbalanced nutrition⁸⁾. A previous study reported that 50~70% of modern diseases are associated with stress while 75% of factors that lead to cardiac disease are due to stress⁹⁾.

The influence of the autonomic nervous system on the sinoatrial node varies according to changes in the internal/external environment. This periodic change in heart rate over time is called heart rate variability (HRV), which refers to the small changes between one cardiac cycle and the next^10,11). A decrease in HRV indicates reduction in the complexity of dynamic changes of the heart rate. This means reduced adaptability of the heart to the changing environment, which may increase the risk of a disease¹²⁾.

In a study related to HRV, Kim¹³⁾ has reported that there are significant differences in HRV between functional and organic dyspepsia. In a study that assessed motion sickness while walking in a virtual reality environment using electrocardiogram, Lee¹⁴⁾ confirmed that the LF/HF ratio was lower in subjects who felt motion sickness. This indicates the activation of the parasympathetic nerve. Given that hypersecretion of acetylcholine causes motion sickness, the relationship between ECG and motion sickness was inferred. Seo¹⁵⁾ examined the association between HRV and hypertension and stress, and published that stress influences the autonomic nervous system as well as hypertension, along with changes in the autonomic nervous system in patients with hypertension.

This study aims to examine whether there is an association between preference for spicy taste and autonomic nervous system function, as measured by HRV. HRV test was conducted along with the preference for spicy taste in 211 subjects. Significant results were obtained after comparative analysis which are reported below.

Subjects, Survey and Analysis Method

Results

1. General characteristics of the subjects

When the general characteristics of the 211 subjects were examined, there were 80 males (37.7%) and 131 females (61.8%). The mean age was 53.85 years with the minimum of 17 years and maximum of 85 years. There were 23 subjects who were between the ages 0 to 29 years (10.9%), 46 subjects between the ages 30 to 49 (21.8%), 79 subjects between the ages 50 and 64 years (37.44%), and 63 subjects aged 65 and older (29.86%). Among them, 55 subjects said that they preferred spicy taste (26.07%) while 72 subjects preferred sweet taste (34.12%), 16 subjects bitter taste (7.58%), 21 subjects sour taste (9.95%) and 24 subjects salty taste (11.37%) (Table 1).

Table 1

The general characteristics of participants

2. HF, LF

HF was significantly lower in the group that preferred spicy taste, as the comparison of HF for the two groups showed a mean of 267.13± 440.39 for the control group and 170.22±215.17 (t=2.41, p=0.017) for the group that preferred spicy taste.

LF was significantly lower in the group that preferred spicy taste as the comparison of LF between the two groups showed a mean of 284.61±492.62 for the control group and 189.89±187.99 (t=2.475, p=0.014) for the group that preferred spicy taste (Fig. 1, Table 2).

Fig. 1

HF, LF

* P<0.05 There were significant lower differences in the spicy preference group (HF, LF).

Table 2

Clinical characteristics of HF, LF by HRV

3. VLF, TP

VLF was lower in the group that preferred spicy taste as the comparison of VLF between the two groups showed a mean of 954.19± 3806.03 for the control group and 463.32±413.62 (t=0.953, p=0.341) for the group that preferred spicy taste.

TP was significantly lower in the group that preferred spicy taste as the comparison of TP between the two groups showed a mean of 1626.29±4512.32 for the control group and 823.43±630.64 (t=2.163, p=0.031) for the group that preferred spicy taste (Fig.2, Table 3).

Fig. 2

VLF, TP

* P<0.05 There was a significant lower difference in the spicy preference group (TP).

There was a lower difference in the spicy preference group, but there was no significant difference (VLF).

Table 3

Clinical characteristics of VLF, TP by HRV

5. RMSSD, LF/HF ratio

RMSSD was significantly lower in the group that preferred spicy taste as the comparison of RMSSD between the two groups showed a mean of 35.24±39.59 for the control group and 25.91±16.59 (t=2.405, p=0.017) for the group that preferred spicy taste.

LF/HF was higher in the group that preferred spicy taste as the comparison of LF/HF between the two groups showed a mean of 1.90±2.03 for the control group and 2.30±2.79 (t=−1.122, p=0.263) for the group that preferred spicy taste (Fig. 3, Table 4).

Fig. 3

RMSSD, LF/HF ratio

* P<0.05 There was a significant lower difference in the spicy preference group (RMSSD).

There was a higher difference in the spicy preference group, but there was no significant difference (LF/HF ratio).

Table 4

Clinical characteristics of LF/HF by HRV

6. ANA, Fatigue

ANA was significantly lower in the group that preferred spicy taste, as the comparison of ANA for the two groups showed a mean of 93.47± 19.41 for the control group and 86.82±11.42 (t=3.042, p=0.002) for the group that preferred spicy taste.

Fatigue was significantly higher in the group that preferred spicy taste as the comparison of fatigue between the two groups showed a mean of 107.03±21.81 for the control group and 114.55±14.50 (t=−2.869, p=0.004) for the group that preferred spicy taste (Fig. 4, Table 5).

Fig. 4

ANA, Fatigue

** P<0.01 There were significant lower differences in the spicy preference group (ANA).

** P<0.01 There were significant higher differences in the spicy preference group (Fatigue).

Table 5

Clinical characteristics of ANA, Fatigue by HRV

Discussion

There has been an increased interest in the changing diet after the COVID-19 pandemic as an attempt to promote public health^16.17). A notable example of a change in diet is the increased consumption of foods for taste and convenience rather than for nutrition, evidenced by the increase in consumption of delivery, processed and retort foods¹⁸⁾. Consequently, restaurants that specialize in simple, spicy taste have been significantly successful.

From ‘buldak’ to street foods such as tteokbokki and chicken skewers to common snacks found in convenience stores have released a ‘spicy’ version, to meet the demand of the consumers that are seeking out spicy taste. This phenomenon goes beyond South Korea. Despite the spiciness that goes beyond general limit, people are craving spicy foods, as evidenced by the popularity of ‘Mouko Tenmen’ from Japan and ‘Ma La Xiang Guo’ from China.

These foods make you sweat due to their extreme spiciness but people seem to enjoy the taste. Particularly, this somehow provokes the feeling of catharsis, leading to the current “spicy food craze”¹⁾. The preference for spicy taste may also be explained by the resistance mechanism for stress or pathogens; however, in the case of the elderly aged 65 or above, studies have shown that excess intake of spicy foods may lead to cognitive decline due to neurotoxicity; however more research is necessary^3,19).

The possibility that autonomic nervous system imbalances might lead to spicy food preference, or that both could be influenced by other factors (e.g., stress, overall diet, lifestyle). But this study aimed to identify the autonomic nerve balance according to spiciness preference by measuring HRV in subjects. When the general characteristics of the 211 subjects were examined, there were 80 males (37.7%) and 131 females (61.8%). The mean age was 53.85 years with the minimum age being 17 years and the maximum age of 85 years. Among them, 55 subjects said that they preferred spicy taste (26.07%) while 72 subjects preferred sweet taste (34.12%), 16 subjects bitter taste (7.58%), 21 subjects sour taste (9.95%) and 24 subjects salty taste (11.37%) (Table 1).

In terms of HF in the 2 groups, HF was significantly lower in the group that preferred spicy taste (Table 2). For HF, wavelengths of 0.15–0.4 Hz were analyzed as the amount of high-frequency components. As an indicator of the activity of the parasympathetic nervous system, the power of the HF component is known to be closely related to the electrical stability of the heart. In patients with aged cardiac function or cases of sudden death due to a heart attack, HF is found to be significantly reduced. In healthy individuals, this is rarely reduced but a significant reduction is observed in cases of persistent stress, terror, anxiety, worry or patients with heart diseases²⁰⁾. Given that HF is significantly reduced in the group that preferred spicy taste, it seems that they preferred spicy taste in order to relieve persistent stress and autonomic nerve imbalance persists as the instability is not resolved despite consuming large quantities of spicy foods.

In terms of LF in the two groups, LF was significantly lower in the group that preferred spicy taste (Table 2). For LF, wavelengths of 0.04–0.15Hz were analyzed as the amount of low frequency components. It simultaneously reflects the activities of the sympathetic and parasympathetic nervous systems, but is mostly used as an indicator of sympathetic nervous system activity. LF is associated with psychological stress, which explains a large amount of the sympathetic nervous system activity that is involved in in vivo energy supply. LF in fatigued condition is reduced, reflecting the loss of energy in the body²¹⁾. In conclusion, the group that prefers spicy taste may experience loss of energy and easily feel fatigued if they consume large quantities of spicy foods given the significantly low level of LF.

VLF was lower in the group that preferred spicy taste as the comparison of VLF between the two groups showed a mean of 954.19± 3806.03 for the control group and 463.32± 413.62 (t=0.953, p=0.341) for the group that preferred spicy taste (Table 3). This domain is the infrasound component that is closely related to the body temperature modulator, and is associated with the renin-angiotensin system, vasomotor, hormonal, and various cardiopulmonary mechanisms. Power of the VLF increases when oxygen exchange is lacking and is typically low in patients with fatigue or arrhythmia. It is more closely related to the various causes of death compared to the LF and HF band, and it has been reported that low power for VLF is associated with arrhythmic death²¹⁾.

VLF did not show any significant change in this test. If significant results of VLF is obtained in my future study, it is considered necessary to conduct a follow-up test through a 24-hour electrocardiogram.

TP was significantly lower in the group that preferred spicy taste as the comparison of TP between the two groups showed a mean of 1626.29±4512.32 for the control group and 823.43±630.64 (t=2.163, p=0.031) for the group that preferred spicy taste (Table 3). TP refers to all power for five minutes, including VLF, LF, and HF. TP reflects the overall activity of the autonomic nervous system as well as the ability to modulate the autonomic nervous system. Typically, in the case of chronic stress or disease, total power is markedly reduced compared to healthy individuals due to the decreased ability to modulate the autonomic nervous system²²⁾. In conclusion, those with a preference for spicy taste may experience reduced ability for autonomic nervous system modulation due to chronic stress.

RMSSD was significantly lower in the group that preferred spicy taste as the comparison of RMSSD between the two groups showed a mean of 35.24±39.59 for the control group and 25.91±16.59 (t=2.405, p=0.017) for the group that preferred spicy taste (Table 4). The activity of the parasympathetic nerve involved with the heart plays a role in the electrical stability of the heart. Compared with healthy individuals, RMSSD is reduced in cases of heart abnormalities or prior to the manifestations of abnormal signs²²⁾. Given that RMSSD was significantly reduced in the group that preferred spicy taste, it is advisable to refrain from continuously consuming spicy foods as it can increase the risk of heart diseases.

LF/HF ratio was higher in the group that preferred spicy taste as the comparison of LF/HF ratio between the two groups showed a mean of 1.90±2.03 for the control group and 2.30±2.79 (t=−1.122, p=0.263) for the group that preferred spicy taste (Table 4). LF/HF ratio is the ratio of low and high frequencies, and reflects the overall balance of the autonomic nervous system, i.e. the sympathetic and parasympathetic nervous system. In some cases, this is used as an indicator of sympathetic nerve activity²³⁾. In conclusion, those with a preference for spicy taste may have increased sympathetic nerve activity and a decreased parasympathetic nerve activity.

ANA was significantly lower in the group that preferred spicy taste as the comparison of ANA between the two groups showed a mean of 93.47±19.41 for the control group and 93.47±19.41 for the group that preferred spicy taste (Table 5). A well-functioning autonomic nervous system is associated with large HRV, as it indicates that adaptation to various changes or in vivo homeostasis is functioning properly²⁴⁾. In conclusion, as the activity of the autonomic nervous system was low in the group that preferred spicy taste, it may suggest that they could experience problems in adapting to various changes or maintaining homeostasis.

Fatigue was significantly higher in the group that preferred spicy taste as the comparison of fatigue between the two groups showed a mean of 107.03±21.81 for the control group and 114.55±14.50 (t=−2.869, p=0.004) for the group that preferred spicy taste (Table 5). As it reflects LF parameters of the wavelength, it shows the physical and psychological fatigue due to stress, and higher levels of fatigue may lead to physical abnormalities such as tiredness, lack of energy and lethargy²⁵⁾. Given that fatigue was higher in the group that preferred spicy taste, it seems likely that their physical and psychological stress is also higher.

As this study used a small to medium-sized sample group with regional limitations, additional research is needed. For those with autonomic nervous system imbalance symptoms, health should be promoted through the intake of all five tastes while refraining from leaning heavily towards the intake of spicy foods. Future attempts will focus on identifying the correlation with physical symptom manifestations due to diet based on one particular taste through continuous research.

Conclustion

This study conducted a HRV test on 211 subjects that visited the local clinic between January and May 2023. The group that preferred spicy taste had 55 subjects and the control group had 156 subjects. Results were compared and analyzed and the conclusion is as follows.

This study observed associations between preference for spicy taste and certain indicators of autonomic nervous system function. Further research is needed to understand the nature and implications of this relationship.

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