Interaction With Indoor Plants Can Reduce Physiological & Psychological Stress

Research Overview: Interaction with indoor plants may reduce psychological and physiological stress by suppressing autonomic nervous system activity in young adults: a randomized crossover study

Summary

This study aimed to investigate the psychological and physiological benefits of interacting with indoor plants in comparison to mental work using a computer task. The study involved 24 young male adults who participated in both a transplanting task with indoor plants and a computer task in a crossover experimental design. The subjects' psychological states were assessed using the semantic differential method, while physiological responses were measured through heart rate variability and blood pressure. The results showed that interacting with indoor plants led to more comfortable, soothed, and natural feelings compared to the computer task. Additionally, the sympathetic nervous system activity and diastolic blood pressure were significantly reduced after the transplanting task. These findings suggest that active interaction with indoor plants can help reduce both psychological and physiological stress when compared to mental work.

I. Background

Did you know that more than 85% of our daily lives are spent indoors? With the rapid advancements in technology, our living spaces have shifted from the outdoors to the indoors, resulting in new challenges for our well-being. The rise of information technology has brought about stress and a phenomenon known as technostress, which refers to the difficulties individuals face in coping with new computer technologies in a healthy manner.

In response to these challenges, researchers have been exploring various ways to manage psychological stress. One area of interest has been the effect of the natural environment on human beings, a topic that has been actively studied since the 1980s. These studies have revealed that interacting with nature, including plants, can have a profound impact on our well-being. In fact, plants have been found to alleviate physiological stress and improve negative psychological symptoms. This is particularly significant because prolonged stress can lead to overactivation of the sympathetic nervous system, which can potentially damage our cardiovascular system.

In recent years, there has been a growing body of evidence supporting the comforting effect of natural environments, prompting further evidence-based studies. Researchers have employed various experimental approaches to quantitatively measure the beneficial effects of natural stimuli, particularly focusing on physiological measures. Engaging with plants offers an intuitive and nonverbal activity that stimulates our senses and provides psychological stability and comfort.

Indoor plants, in particular, have captured the attention of the scientific community due to their wide range of benefits. Several studies have shown that indoor plants can:

• Enhance job satisfaction among office workers.
• Reduce psychological stress.
• Improve mood states.
• Enhance cognitive health.

These positive effects can potentially enhance our resistance to diseases and chronic stress. However, it is important to note that while these benefits are promising, further rigorous evidence is still needed.

With the current methods of psychological assessment, it is challenging to fully explain the health benefits of indoor plants. Additionally, few studies have delved into the physiological mechanisms underlying these benefits. Therefore, this study aims to investigate the physiological benefits of indoor plants on modern individuals. Specifically, the focus is on examining cardiovascular changes and measuring autonomic nervous system activity when individuals come into contact with foliage plants. Furthermore, this study seeks to quantify the psychological changes that occur during this interaction with plants.

By understanding the physiological and psychological benefits of indoor plants, we can uncover their potential in promoting overall well-being and improving our quality of life.

II. Methods

To uncover the physiological benefits of indoor plants, a group of 24 young male adults, with an average age of 24.9 ± 2.1 years, were enrolled as participants in this study. It is important to note that none of the subjects reported any history of physical or psychiatric disorders, ensuring a relatively healthy sample for the experiment. The study spanned a duration of three days, during which strict guidelines were followed to maintain consistency and accuracy.

During the study, participants were prohibited from consuming alcohol and tobacco, and their caffeine intake was controlled. These measures were put in place to eliminate potential confounding factors that could affect the results. Furthermore, prior to the commencement of the experiments, the subjects were provided with comprehensive information regarding the aims and procedures of the study. Informed consent was obtained from each participant, ensuring their voluntary participation. The study was conducted in compliance with the regulations set forth by the Clinical Trial Center at Chungnam National University Hospital in Korea and the Ethics Committee of the Center for Environment, Health, and Field Sciences at Chiba University in Japan.

The study employed a crossover experimental design, which allowed for a comparison of physiological responses between two different tasks. The 24 subjects were randomly divided into two groups, each consisting of 12 participants. On the first day of the experiments, the first group engaged in tending to indoor plants, while the second group worked on a document using a word processor. The word processor task was chosen as it represents one of the most typical computer tasks that require continuous physical activity, somewhat akin to the transplanting task involved in tending to plants. On the second day, the groups switched activities, ensuring that each participant had the opportunity to perform both tasks. Importantly, each subject performed each task at the same time of the day to mitigate the potential effects of diurnal variation.

By employing this well-designed experimental approach, the study aimed to provide valuable insights into the physiological responses associated with interacting with indoor plants. The rigorous methodology and careful consideration of participant selection ensure the reliability and validity of the findings. In the next section, we will delve into the specific results of the study, shedding light on the fascinating physiological changes that occur when we come into contact with indoor plants. Stay tuned!

III. Materials

To assess the physiological changes occurring during the tasks, specific measurements were taken from the subjects. In the waiting room, an electrode was attached to the subjects' chests to monitor their heart activity. They were then instructed to move to the experimental room. After a 2-minute rest in a seated position to establish a baseline, the subjects began performing their respective tasks: transplanting houseplants or engaging in computer work. The duration of each task was set at 15 minutes.

During the tasks, heart rate variability (HRV) was continuously measured using a portable electrocardiograph called Activtracer AC-301A, manufactured by GMS in Tokyo, Japan. HRV is a valuable indicator of autonomic nervous system activity and provides insights into physiological responses to stress and relaxation. By monitoring HRV, the researchers could assess changes in the subjects' cardiovascular functioning during the tasks.

In addition to HRV, blood pressure and pulse rate data were collected before and after the tasks. A digital blood pressure monitoring device, specifically the HEM-1000 by OMRON in Kyoto, Japan, was used for this purpose. This allowed the researchers to gather comprehensive information on the subjects' cardiovascular parameters and evaluate any changes resulting from their engagement in the assigned tasks.

By employing these measurement techniques, the researchers were able to gather objective physiological data, providing valuable insights into the effects of transplanting houseplants and computer work on the participants' cardiovascular functioning. In the following section, we will delve into the results and implications of the study, shedding light on the potential benefits of engaging with indoor plants.

V. Data Analysis

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To analyze the collected data and draw meaningful conclusions, various statistical methods were employed. The analysis focused on heart rate variability (HRV) data, subjective ratings of feelings, and blood pressure measurements. The specific procedures and statistical tests used are outlined below.

1. Heart Rate Variability (HRV) Analysis:

   • The HRV data were processed by calculating the average inter-beat (R-R) data in 1-minute intervals.
   • Maximum entropy methods, specifically MemCalc by GMS in Tokyo, Japan, were utilized to analyze the power spectrum of the HRV data.
   • The power spectrum was divided into two frequency components: low-frequency (LF; 0.04 to 0.14 Hz) and high-frequency (HF; 0.15 to 0.40 Hz).
   • The HF component reflects parasympathetic nervous system activity, which is associated with relaxation.
   • The LF/(LF + HF) ratio indicates sympathetic nervous system activity, which is linked to stress.
   • All HRV values were log-transformed using a base 10 logarithm to facilitate analysis.

2. Subjective Ratings of Feelings:

   • The subjects' subjective feelings were assessed using the semantic differential method (SDM).
   • The SDM involved self-rating assessments on a seven-point scale for three specific test items: 'Comfortable,' 'Relaxed,' and 'Natural.'
   • The subjects were asked to write down their feelings before and after completing the tasks.

3. Statistical Analysis:

   • Statistical analysis was conducted to compare the differences in HRV values, blood pressure, and psychological data between the two tasks.
   • A paired t-test was employed for comparing HRV values and blood pressure.
   • The Wilcoxon signed-rank test was used for analyzing psychological data.
   • The statistical software SPSS, version 21.0 by IBM Corp. in Chicago, IL, USA, was utilized for all statistical analyses.
   • One-sided tests were applied based on the hypothesis that the subjects would feel more relaxed after the transplanting task.
   • Statistical significance was determined at a threshold of P < 0.05.

By applying these rigorous statistical methods to the collected data, the researchers were able to examine the physiological and psychological effects of engaging with indoor plants compared to computer work. In the subsequent section, we will explore the findings and implications of this study, shedding light on the potential benefits of incorporating indoor plants into our living and working environments.

VI. Results

The research findings provide valuable insights into the physiological and psychological effects of engaging with indoor plants compared to computer work. The results of the study are presented below, highlighting the differences observed between the two tasks.

1. Subjective Feelings:

   • After the transplanting task, subjects reported feeling comfortable, soothed, and natural.
   • After the computer task, they expressed feelings of discomfort, awakeness, and artificiality.
   • Significant differences were observed for these feelings after the 15-minute tasks, indicating that engaging with indoor plants induced positive emotional responses, while computer work resulted in less favorable feelings.

2. Sympathetic Nervous System Activity:

   • Changes in log[LF/(LF + HF)] values, reflecting sympathetic nervous system activity, were examined.
   • Although the mean values of total log[LF/(LF + HF)] for the 15-minute period did not show significant differences, the patterns of change varied between the two tasks.
   • The log[LF/(LF + HF)] value increased over time during the computer task but decreased toward the end of the transplanting task.
   • A significant difference in log[LF/(LF + HF)] values was found between the transplanting task and the computer task during the last 3 minutes of the tasks.

3. Diastolic Blood Pressure:

   • Diastolic blood pressure analysis indicated a significant difference between the transplanting task and the computer task upon task completion.
   • The transplanting task resulted in lower diastolic blood pressure compared to the computer task.

These results suggest that engaging with indoor plants, as exemplified by the transplanting task, positively impacts physiological responses related to stress. The decrease in log[LF/(LF + HF)] values and the lower diastolic blood pressure observed during the transplanting task indicate a relaxation response associated with reduced sympathetic nervous system activity. Conversely, the computer task showed an increase in log[LF/(LF + HF)] values and higher diastolic blood pressure, suggesting a more stressed state.

These findings contribute to our understanding of the potential benefits of indoor plants on human well-being. In the following section, we will discuss the implications of these results and how they can be applied to promote a healthier and more balanced indoor environment.

VII. Discussion

The research findings demonstrate the stress-reducing effects of interaction with indoor foliage plants, as evidenced by the analysis of physiological and psychological responses. The results indicate that indoor plants have a positive impact on the autonomic nervous system, specifically by suppressing sympathetic activity, which tends to increase in response to stressors. The value of log[LF/(LF + HF)], which reflects sympathetic activity, initially increases when subjects start either the transplanting or computer task, but shows a slow decrease during the transplanting task while consistently increasing during the computer task. Notably, the stress-reducing effect was observed at the end of the transplanting task, which aligns with previous studies. However, it is important to note that this finding is based on a comparison with a computer task, a mental task known to increase sympathetic activity.

The positive feelings reported by the subjects during interaction with indoor plants further support the notion that indoor plants have beneficial effects on human well-being. In contrast, the computer task resulted in increased diastolic blood pressure and sympathetic nervous system activity, indicating a more stressed psychological state. The self-rating SDM scores also indicated that working on a computer had negative effects on the psychological state of the subjects. Interestingly, even though the transplanting task was unfamiliar to the subjects, they still experienced less stress compared to the computer task.

The data from this study contribute to understanding the positive physiological and psychological benefits of active interaction with indoor plants. While previous studies have mainly focused on the benefits of passive interaction with indoor plants, our research sheds light on the mechanisms underlying the health benefits of active engagement with indoor plants, particularly in relation to stress responses. The multiple natural stimuli provided by indoor plants, such as visual, auditory, tactile, and olfactory stimuli, likely contribute to these physiological benefits. This is consistent with research on forest therapy, which has also demonstrated similar positive effects on stress reduction through exposure to natural environments.

It is important to acknowledge the limitations of this study. The subject group consisted only of healthy young male university students, limiting the generalizability of the results. Future studies should include more diverse subject groups to ensure the broader applicability of the findings. Additionally, the duration of the tasks (15 minutes) may have influenced the timing of the observed physiological responses, and it would be beneficial to extend the task duration in future research. Furthermore, using a control task that is more realistic and applicable to real-life scenarios would provide valuable insights for the practical application of the study's results.

In conclusion, this study provides evidence of the stress-reducing effects of active interaction with indoor plants, highlighting the positive physiological and psychological benefits. The findings contribute to our understanding of the potential role of indoor plants in promoting human well-being and suggest avenues for further research and practical applications in creating healthier indoor environments.

VIII. Conclusion

The findings of this study indicate that active interaction with indoor plants can effectively reduce both physiological and psychological stress when compared to engaging in mental work, such as computer tasks. The stress reduction is achieved through the suppression of sympathetic nervous system activity and diastolic blood pressure, as well as the promotion of comfortable, soothed, and natural feelings among individuals.

The results support the idea that incorporating indoor plants into indoor environments can have significant benefits for human well-being. By actively engaging with indoor plants, individuals can experience a reduction in stress levels and enjoy a more relaxed state. These findings highlight the importance of considering indoor plants as a means to create healthier and more supportive environments, particularly in settings where individuals are exposed to high levels of mental stress.

Overall, this study contributes to the growing body of evidence that emphasizes the positive effects of indoor plants on human health and well-being. The results suggest that incorporating indoor plants into various indoor settings, such as offices, homes, and public spaces, can offer a viable strategy for reducing stress and promoting a more favorable psychological state. Further research involving diverse subject groups and longer task durations would be valuable in confirming and expanding upon these findings. By better understanding the mechanisms and benefits of active interaction with indoor plants, we can explore practical applications to optimize indoor environments and enhance the overall quality of life for individuals.

Reference: 

Lee, Ms., Lee, J., Park, BJ. et al. Interaction with indoor plants may reduce psychological and physiological stress by suppressing autonomic nervous system activity in young adults: a randomized crossover study. J Physiol Anthropol 34, 21 (2015). https://doi.org/10.1186/s40101-015-0060-8