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ORIGINAL ARTICLE
The Relationship Between Nature-Based Tourism and Autonomic Nervous System Function Among Older Adults Liang-Chih Chang, PhD Department of Living Sciences, National Open University, New Taipei City, Taiwan DOI: 10.1111/jtm.12108
See the Editorial by Sebastian Filep, pp. 150–152 of this issue.
Background. Nature-based tourism has recently become a topic of interest in health research. This study was aimed at examining relationships among nature-based tourism, stress, and the function of the autonomic nervous system (ANS). Methods. Three hundred and twenty-two older adults living in Taichung City, Taiwan, were selected as participants. Data were collected by a face-to-face survey that included measures of the frequency of participation in domestic and international nature-based tourism and the stress and ANS function of these participants. The data were analyzed using a path analysis. Results. The results demonstrated that the frequency of participation in domestic nature-based tourism directly contributed to ANS function and that it also indirectly contributed to ANS function through stress reduction. Conclusions. Domestic nature-based tourism can directly and indirectly contribute to ANS function among older adults. Increasing the frequency of participation in domestic nature-based tourism should be considered a critical element of health programs for older adults.
D
ysfunction in the autonomic nervous system (ANS) can lead to health complications, such as cardiovascular disease1 and migraine headaches.2 Aging is a physiological process related to negative functional changes in ANS.3,4 Thus, it is crucial that older adults maintain ANS function to reduce the risk of disease.1,5 A rapid decline in ANS function among older adults can be attributed to a lack of physical activity,6 significant changes in diurnal temperature,7 nutritional deficiencies,8 poor sleep habits,9 and stress.10 Recent studies have further reported that the amounts of physical activity and stress have the greatest influence on ANS function.11,12 Therefore, maintaining healthy ANS function requires that older adults increase their frequency of physical activity and decrease their levels of stress. Participation in nature-based tourism, which often involves physical activity, may promote the health of tourists.13 Nature-based tourism refers to activities performed by tourists while on vacation or enjoying leisure time with a focus on enjoying natural attractions. Corresponding Author: Liang-Chih Chang, PhD, Department of Living Sciences, National Open University, 172, Zhongzheng Road, Luzhou, New Taipei City 247, Taiwan. E-mail: [email protected]
Bird watching, fishing, and walking in forests are typical examples of nature-based tourism.14,15 Such activities are distinct from those performed during everyday leisure activities because they are specifically designed to facilitate the enjoyment of natural attractions. For example, walking in an urban park may yield the enjoyment of the environment, but it is not necessarily the purpose or result of that walk. As mentioned in previous studies, vacations incorporating physical activity,16 – 18 such as skiing19 and walking tours,13 can have a considerable positive effect on physical and psychological health. Thus, if physical activity does contribute to improvements in ANS function among older adults,6 the frequency of participation in nature-based tourism should be positively related to their ANS function. Nature-based tourism can be divided into domestic and international activities. Little work has been done to compare the benefits of participation in domestic tourism with those of international tourism. Therefore, it is important to examine whether there are significant differences in the benefits of participation in these two types of nature-based tourisms. Furthermore, exposure to natural environments can promote relaxation, thereby relieving stress.20,21 It appears that coming into contact with nature through participation in nature-based tourism may also © 2014 International Society of Travel Medicine, 1195-1982 Journal of Travel Medicine 2014; Volume 21 (Issue 3): 159–162
160
reduce stress. Because stress significantly negatively influences ANS function among older adults,10 the frequency of participation in nature-based tourism may indirectly contribute to improvements in ANS function through stress reduction. However, no previous studies have examined the relationships among the frequency of participation in nature-based tourism, stress, and ANS function, thus making the relationships worthy of further investigation. The results of this investigation provide health care practitioners with information valuable to the development of strategies for maintaining healthy ANS function among older adults. Methods The relationship between nature-based tourism and ANS function is based on the assumption that a higher frequency of participation in nature-based tourism can lead to improved ANS function. Therefore, this study recruited participants who were actively involved in programs for older adults. The programs included activities such as dancing, karaoke, and walking tours, and participation in the programs increased the likelihood that these participants were engaged in nature-based tourism. The programs were conducted by the Social Affairs Bureau of Taichung City, Taiwan, and relevant officials helped in the recruitment of participants. Participants had to meet two eligibility criteria: (1) aged ≥65 years and (2) able to participate in nature-based tourism. Three hundred and twenty-two older adults were recruited. The participants in this study were aged 65 to 89, with a mean age of 76.2 years (SD = 6.58). This included 193 women (59.9%) and 129 men (40.1%). Among them, 62 (19.2%) were illiterate, 204 (63.4%) were primary school graduates, 36 (11.2%) were high school graduates, and 20 (6.2%) had a university degree or higher. In addition, 4 (1.2%) were unmarried, 9 (2.8%) were divorced, 140 (43.5%) were widowed, and 169 (52.5%) were married. To ensure the quality of data, a face-to-face survey was conducted. The participants were asked the following questions to measure the frequency of participation in domestic and international nature-based tourism: (1) How many times did you undertake naturebased tourism in Taiwan in the last month? (2) How many times did you undertake nature-based tourism abroad in the last month? Frequency was coded as 0 = no, 1 = once . . . , and 30 = 30 times. Stress and ANS function were measured using an electrocardiogram (SA-3000P, Medi-Core, Seoul, South Korea), which is used widely to analyze heart rate variability (HRV) related to stress status and ANS function.4,7,22 HRV parameters are calculated on normal-to-normal (NN) inter-beat intervals (or NN intervals) caused by normal heart contractions, paced by sinus node depolarization (the operation manual of SA-3000P). J Travel Med 2014; 21: 159–162
Chang
Participants were allowed to rest for 30 minutes before conducting electrocardiographic recordings over a period of approximately 5 minutes. Stress was assessed according to the physical stress index (PSI), which reflects the accumulated outcome of load and pressure on the heart. Participants with stress scores exceeding 50 were deemed to be under the effects of stress. ANS function was assessed according to the square root of the mean squared differences of successive NN intervals (RMSSD), power in the low frequency range (LF), and power in the high frequency range (HF). RMSSD estimates high-frequency variations in heart rate according to short-term NN recordings (measured in milliseconds) as an estimate of the parasympathetic regulation of the heart. Participants with an RMSSD value of less than 20 were deemed to suffer from ANS dysfunction. LF is a band in the power spectrum between 0.04 and 0.15 Hz and presents an effective predictor of sympathetic activity, calculated in milliseconds squared (ms2 ). HF is a band in the power spectrum between 0.15 and 0.4 Hz as an indicator of parasympathetic activity, calculated in milliseconds squared (ms2 ). An LF/HF ratio of less than 0.5 or more than 2 among participants was deemed an indication of ANS dysfunction. After collecting the study data, a correlation analysis was performed to examine the relationships among the frequency of participation in domestic and international nature-based tourism, stress, and ANS function. A path analysis was then conducted to determine whether the frequency of participation directly contributed to ANS function and whether it also indirectly contributed to ANS function through stress reduction. Results The LF/HF ratio of 153 participants was less than 0.5 or more than 2. In other words, the prevalence of ANS dysfunction was 47.5% among older adults with active lifestyles. The average scores for the frequency of participation in domestic and international nature-based tourism were 4.01 (SD = 1.63) and 0.07 (SD = 0.25), respectively. The average scores for stress and ANS function were 110.07 (SD = 144.60) and 33.94 (SD = 30.46), respectively. The results of the correlation analysis revealed that the frequency of participation in domestic nature-based tourism was significantly related to stress and ANS function, whereas the frequency of participation in international naturebased tourism was only weakly related to stress and ANS function (Table 1). The results derived from the path analysis were as follows: (1) the frequency of participation in domestic nature-based tourism directly contributed to ANS function, (2) the frequency of participation in domestic nature-based tourism also indirectly contributed to ANS function through stress reduction, and (3) the frequency of participation in international nature-based tourism did not contribute to both stress reduction and ANS function (Figure 1).
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Nature-Based Tourism and ANS Function Table 1
Correlation coefficients of variables
Variables
1
2
1. Domestic nature-based tourism — — 2. International nature-based tourism 0.13* 3. Stress −0.30** −0.11* 0.12* 4. ANS function 0.32** *
3
— −0.43**
4
—
**
p < 0.05, p < 0.01.
Figure 1 Path coefficients of variables. **p < 0.01.
Discussion As reported in previous studies, the positive effect of physical activity on ANS function among older adults is considerable.6,11 The results of this study also indicated that the frequency of participation in domestic naturebased tourism was positively related to ANS function and that the former significantly contributed to the latter in the path model. It appears that participation in nature-based tourism is an effective way to help older adults maintain healthy ANS function. Consistent with the previous findings that exposure to natural environments can enable older adults to relieve stress,20,21 the results of the correlation analysis revealed that the frequency of participation in domestic nature-based tourism had a significant negative correlation with stress. The path model in this study further demonstrates that the frequency of participation in domestic nature-based tourism can significantly contribute to maintaining healthy ANS function through stress reduction. According to the above results, increasing the frequency of participation in domestic nature-based tourism should be considered a critical element of health programs for older adults. Furthermore, domestic nature-based tourism is distinct from the everyday leisure activities performed in natural environments such as walking in urban parks. As previously mentioned, domestic nature-based tourism involves the contact with and appreciation of nature more than everyday leisure activities do. This contact and appreciation may yield pleasurable experiences that supplement the routines of daily life and relieve stress, which significantly negatively affects ANS function. Thus, participation in domestic nature-based tourism, which can provide the benefits of both physical activity and stress relief, is more important for older adults, compared with participation in leisure-time physical activity.
However, the frequency of participation in international nature-based tourism did not make a significant contribution to both stress reduction and ANS function in the path model. A path analysis is able to eliminate spurious predictors when significant predictors are entered into the statistical model;23 therefore, the results imply that domestic nature-based tourism has a more pronounced effect on the maintenance of ANS function, compared with international nature-based tourism. Nonetheless, among the participants in this study, international nature-based tourism was very infrequent (only 6.5% of them had traveled abroad); therefore, the results failed to provide sufficient statistical variance to generate precise results. Accordingly, the relationship between international nature-based tourism and ANS function among older adults requires further investigation. One must be cautious in the interpretation of the above results, due to the limitations of this study. First, cause–effect conclusions cannot be drawn directly from the results of this correlational analysis. Second, the results cannot be generalized directly to older adults with a sedentary lifestyle because the participants were selected from a specific subset. If one accepts the underlying premise of this study, however, the results are still valuable, elucidating the relationship between nature-based tourism and ANS function among older adults. Acknowledgment This study was funded by National Science Council in Taiwan (NSC 101-2410-H-180-001). Declaration of Interests The author states he has no conflicts of interest to declare. References 1. Kop WJ, Stein PK, Tracy RP, et al. Autonomic nervous system dysfunction and inflammation contribute to the increased cardiovascular mortality risk associated with depression. Psychosom Med 2010; 72:626–635. 2. Shechter A, Stewart WF, Silberstein SD, Lipton RB. Migraine and autonomic nervous system function: a population-based, case–control study. Neurology 2002; 58:422–427. 3. Lipsitz LA, Mietus J, Moody GB, Goldberger AL. Spectral characteristics of heart rate variability before and during postural tilt: relations to aging and risk of syncope. Circulation 1990; 81:1803–1810. 4. Yu S, Katoh T, Makino H, et al. Age and heart rate variability after soccer games. Res Sports Med 2010; 18:263–269. 5. Acharya UR, Joseph KP, Kannathal N, et al. Heart rate variability: a review. Med Biol Eng Comput 2006; 44:1031–1051. J Travel Med 2014; 21: 159–162
162 6. Lu W, Kuo C. Comparison of the effects of Tai Chi Chuan and Wai Tan Kung exercises on autonomic nervous system modulation and on hemodynamics in elder adults. Am J Chin Med 2006; 34:959–968. 7. Lim YH, Kim H, Kim JH, et al. Effect of diurnal temperature range on cardiovascular markers in the elderly in Seoul, Korea. Int J Biometeorol 2013; 57: 597–603. 8. Holguin F, T´ellez-Rojo MM, Lazo M, et al. Cardiac autonomic changes associated with fish oil vs soy oil supplementation in the elderly. Chest 2005; 127:1102–1107. 9. Wolk R, Gami AS, Garcia-Touchard A, Somers VK. Sleep and cardiovascular disease. Curr Probl Cardiol 2005; 30:625–662. 10. Cacioppo JT, Berntson GG, Malarkey WB, et al. Autonomic, neuroendocrine, and immune responses to psychological stress: the reactivity hypothesis. Ann N Y Acad Sci 1998; 840:664–673. 11. Lee I. Autonomic nervous system dysfunction. Taipei: Hao Wen Co., Ltd., 1997. 12. Kuo Y. Improving autonomic nervous system function. Taipei: Persimmonbooks, 2012. 13. Strauss-Blasche G, Riedmann B, Schobersberger W, et al. Vacation at moderate and low altitude improves perceived health in individuals with metabolic syndrome. J Travel Med 2004; 11:300–306. 14. Fredmana P, Tyrv¨ainenbc L. Frontiers in nature-based tourism. Scand J Hosp Tour 2010; 10:177–189.
J Travel Med 2014; 21: 159–162
Chang 15. Arnegger J, Woltering M, Job H. Toward a productbased typology for nature-based tourism: a conceptual framework. J Sustain Tour 2010; 18:915–928. 16. Eaker ED, Pinsky J, Castelli WP. Myocardial infarction and coronary death among women: psychosocial predictors from a 20-year follow-up of women in the Framingham study. Am J Epidemiol 1992; 135:854–864. 17. Gump BB, Matthews KA. Are vacations good for your health? The 9-year mortality experience after the multiple risk factor intervention trial. Psychosom Med 2000; 62:608–612. 18. Strauss-Blasche G, Reithofer B, Schobersberger W, et al. Effect of vacation on health: moderating factors of vacation outcome. J Travel Med 2005; 12:94–101. 19. de Bloom J, Geurts SA, Sonnentag S, et al. How does a vacation from work affect employee health and well-being? Psychol Health 2011; 26:1606–1622. 20. Bowler DE, Buyung-Ali LM, Knight TM, Pullin AS. A systematic review of evidence for the added benefits to health of exposure to natural environments. BMC Public Health 2010; 10:456. 21. Berto R. Assessing the restorative value of the environment: a study on the elderly in comparison with young adults and adolescents. Int J Psychol 2007; 42:331–341. 22. Huang F, Chien D, Chung U. Effects of Hatha yoga on stress in middle-aged women. J Nurs Res 2013; 21:59–66. 23. Kutner MH, Nachtsheim CJ, Neter J, Li W. Applied linear statistical models. New York: McGraw-Hill, 2005.
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ORIGINAL ARTICLE
The Relationship Between Nature-Based Tourism and Autonomic Nervous System Function Among Older Adults Liang-Chih Chang, PhD Department of Living Sciences, National Open University, New Taipei City, Taiwan DOI: 10.1111/jtm.12108
See the Editorial by Sebastian Filep, pp. 150–152 of this issue.
Background. Nature-based tourism has recently become a topic of interest in health research. This study was aimed at examining relationships among nature-based tourism, stress, and the function of the autonomic nervous system (ANS). Methods. Three hundred and twenty-two older adults living in Taichung City, Taiwan, were selected as participants. Data were collected by a face-to-face survey that included measures of the frequency of participation in domestic and international nature-based tourism and the stress and ANS function of these participants. The data were analyzed using a path analysis. Results. The results demonstrated that the frequency of participation in domestic nature-based tourism directly contributed to ANS function and that it also indirectly contributed to ANS function through stress reduction. Conclusions. Domestic nature-based tourism can directly and indirectly contribute to ANS function among older adults. Increasing the frequency of participation in domestic nature-based tourism should be considered a critical element of health programs for older adults.
D
ysfunction in the autonomic nervous system (ANS) can lead to health complications, such as cardiovascular disease1 and migraine headaches.2 Aging is a physiological process related to negative functional changes in ANS.3,4 Thus, it is crucial that older adults maintain ANS function to reduce the risk of disease.1,5 A rapid decline in ANS function among older adults can be attributed to a lack of physical activity,6 significant changes in diurnal temperature,7 nutritional deficiencies,8 poor sleep habits,9 and stress.10 Recent studies have further reported that the amounts of physical activity and stress have the greatest influence on ANS function.11,12 Therefore, maintaining healthy ANS function requires that older adults increase their frequency of physical activity and decrease their levels of stress. Participation in nature-based tourism, which often involves physical activity, may promote the health of tourists.13 Nature-based tourism refers to activities performed by tourists while on vacation or enjoying leisure time with a focus on enjoying natural attractions. Corresponding Author: Liang-Chih Chang, PhD, Department of Living Sciences, National Open University, 172, Zhongzheng Road, Luzhou, New Taipei City 247, Taiwan. E-mail: [email protected]
Bird watching, fishing, and walking in forests are typical examples of nature-based tourism.14,15 Such activities are distinct from those performed during everyday leisure activities because they are specifically designed to facilitate the enjoyment of natural attractions. For example, walking in an urban park may yield the enjoyment of the environment, but it is not necessarily the purpose or result of that walk. As mentioned in previous studies, vacations incorporating physical activity,16 – 18 such as skiing19 and walking tours,13 can have a considerable positive effect on physical and psychological health. Thus, if physical activity does contribute to improvements in ANS function among older adults,6 the frequency of participation in nature-based tourism should be positively related to their ANS function. Nature-based tourism can be divided into domestic and international activities. Little work has been done to compare the benefits of participation in domestic tourism with those of international tourism. Therefore, it is important to examine whether there are significant differences in the benefits of participation in these two types of nature-based tourisms. Furthermore, exposure to natural environments can promote relaxation, thereby relieving stress.20,21 It appears that coming into contact with nature through participation in nature-based tourism may also © 2014 International Society of Travel Medicine, 1195-1982 Journal of Travel Medicine 2014; Volume 21 (Issue 3): 159–162
160
reduce stress. Because stress significantly negatively influences ANS function among older adults,10 the frequency of participation in nature-based tourism may indirectly contribute to improvements in ANS function through stress reduction. However, no previous studies have examined the relationships among the frequency of participation in nature-based tourism, stress, and ANS function, thus making the relationships worthy of further investigation. The results of this investigation provide health care practitioners with information valuable to the development of strategies for maintaining healthy ANS function among older adults. Methods The relationship between nature-based tourism and ANS function is based on the assumption that a higher frequency of participation in nature-based tourism can lead to improved ANS function. Therefore, this study recruited participants who were actively involved in programs for older adults. The programs included activities such as dancing, karaoke, and walking tours, and participation in the programs increased the likelihood that these participants were engaged in nature-based tourism. The programs were conducted by the Social Affairs Bureau of Taichung City, Taiwan, and relevant officials helped in the recruitment of participants. Participants had to meet two eligibility criteria: (1) aged ≥65 years and (2) able to participate in nature-based tourism. Three hundred and twenty-two older adults were recruited. The participants in this study were aged 65 to 89, with a mean age of 76.2 years (SD = 6.58). This included 193 women (59.9%) and 129 men (40.1%). Among them, 62 (19.2%) were illiterate, 204 (63.4%) were primary school graduates, 36 (11.2%) were high school graduates, and 20 (6.2%) had a university degree or higher. In addition, 4 (1.2%) were unmarried, 9 (2.8%) were divorced, 140 (43.5%) were widowed, and 169 (52.5%) were married. To ensure the quality of data, a face-to-face survey was conducted. The participants were asked the following questions to measure the frequency of participation in domestic and international nature-based tourism: (1) How many times did you undertake naturebased tourism in Taiwan in the last month? (2) How many times did you undertake nature-based tourism abroad in the last month? Frequency was coded as 0 = no, 1 = once . . . , and 30 = 30 times. Stress and ANS function were measured using an electrocardiogram (SA-3000P, Medi-Core, Seoul, South Korea), which is used widely to analyze heart rate variability (HRV) related to stress status and ANS function.4,7,22 HRV parameters are calculated on normal-to-normal (NN) inter-beat intervals (or NN intervals) caused by normal heart contractions, paced by sinus node depolarization (the operation manual of SA-3000P). J Travel Med 2014; 21: 159–162
Chang
Participants were allowed to rest for 30 minutes before conducting electrocardiographic recordings over a period of approximately 5 minutes. Stress was assessed according to the physical stress index (PSI), which reflects the accumulated outcome of load and pressure on the heart. Participants with stress scores exceeding 50 were deemed to be under the effects of stress. ANS function was assessed according to the square root of the mean squared differences of successive NN intervals (RMSSD), power in the low frequency range (LF), and power in the high frequency range (HF). RMSSD estimates high-frequency variations in heart rate according to short-term NN recordings (measured in milliseconds) as an estimate of the parasympathetic regulation of the heart. Participants with an RMSSD value of less than 20 were deemed to suffer from ANS dysfunction. LF is a band in the power spectrum between 0.04 and 0.15 Hz and presents an effective predictor of sympathetic activity, calculated in milliseconds squared (ms2 ). HF is a band in the power spectrum between 0.15 and 0.4 Hz as an indicator of parasympathetic activity, calculated in milliseconds squared (ms2 ). An LF/HF ratio of less than 0.5 or more than 2 among participants was deemed an indication of ANS dysfunction. After collecting the study data, a correlation analysis was performed to examine the relationships among the frequency of participation in domestic and international nature-based tourism, stress, and ANS function. A path analysis was then conducted to determine whether the frequency of participation directly contributed to ANS function and whether it also indirectly contributed to ANS function through stress reduction. Results The LF/HF ratio of 153 participants was less than 0.5 or more than 2. In other words, the prevalence of ANS dysfunction was 47.5% among older adults with active lifestyles. The average scores for the frequency of participation in domestic and international nature-based tourism were 4.01 (SD = 1.63) and 0.07 (SD = 0.25), respectively. The average scores for stress and ANS function were 110.07 (SD = 144.60) and 33.94 (SD = 30.46), respectively. The results of the correlation analysis revealed that the frequency of participation in domestic nature-based tourism was significantly related to stress and ANS function, whereas the frequency of participation in international naturebased tourism was only weakly related to stress and ANS function (Table 1). The results derived from the path analysis were as follows: (1) the frequency of participation in domestic nature-based tourism directly contributed to ANS function, (2) the frequency of participation in domestic nature-based tourism also indirectly contributed to ANS function through stress reduction, and (3) the frequency of participation in international nature-based tourism did not contribute to both stress reduction and ANS function (Figure 1).
161
Nature-Based Tourism and ANS Function Table 1
Correlation coefficients of variables
Variables
1
2
1. Domestic nature-based tourism — — 2. International nature-based tourism 0.13* 3. Stress −0.30** −0.11* 0.12* 4. ANS function 0.32** *
3
— −0.43**
4
—
**
p < 0.05, p < 0.01.
Figure 1 Path coefficients of variables. **p < 0.01.
Discussion As reported in previous studies, the positive effect of physical activity on ANS function among older adults is considerable.6,11 The results of this study also indicated that the frequency of participation in domestic naturebased tourism was positively related to ANS function and that the former significantly contributed to the latter in the path model. It appears that participation in nature-based tourism is an effective way to help older adults maintain healthy ANS function. Consistent with the previous findings that exposure to natural environments can enable older adults to relieve stress,20,21 the results of the correlation analysis revealed that the frequency of participation in domestic nature-based tourism had a significant negative correlation with stress. The path model in this study further demonstrates that the frequency of participation in domestic nature-based tourism can significantly contribute to maintaining healthy ANS function through stress reduction. According to the above results, increasing the frequency of participation in domestic nature-based tourism should be considered a critical element of health programs for older adults. Furthermore, domestic nature-based tourism is distinct from the everyday leisure activities performed in natural environments such as walking in urban parks. As previously mentioned, domestic nature-based tourism involves the contact with and appreciation of nature more than everyday leisure activities do. This contact and appreciation may yield pleasurable experiences that supplement the routines of daily life and relieve stress, which significantly negatively affects ANS function. Thus, participation in domestic nature-based tourism, which can provide the benefits of both physical activity and stress relief, is more important for older adults, compared with participation in leisure-time physical activity.
However, the frequency of participation in international nature-based tourism did not make a significant contribution to both stress reduction and ANS function in the path model. A path analysis is able to eliminate spurious predictors when significant predictors are entered into the statistical model;23 therefore, the results imply that domestic nature-based tourism has a more pronounced effect on the maintenance of ANS function, compared with international nature-based tourism. Nonetheless, among the participants in this study, international nature-based tourism was very infrequent (only 6.5% of them had traveled abroad); therefore, the results failed to provide sufficient statistical variance to generate precise results. Accordingly, the relationship between international nature-based tourism and ANS function among older adults requires further investigation. One must be cautious in the interpretation of the above results, due to the limitations of this study. First, cause–effect conclusions cannot be drawn directly from the results of this correlational analysis. Second, the results cannot be generalized directly to older adults with a sedentary lifestyle because the participants were selected from a specific subset. If one accepts the underlying premise of this study, however, the results are still valuable, elucidating the relationship between nature-based tourism and ANS function among older adults. Acknowledgment This study was funded by National Science Council in Taiwan (NSC 101-2410-H-180-001). Declaration of Interests The author states he has no conflicts of interest to declare. References 1. Kop WJ, Stein PK, Tracy RP, et al. Autonomic nervous system dysfunction and inflammation contribute to the increased cardiovascular mortality risk associated with depression. Psychosom Med 2010; 72:626–635. 2. Shechter A, Stewart WF, Silberstein SD, Lipton RB. Migraine and autonomic nervous system function: a population-based, case–control study. Neurology 2002; 58:422–427. 3. Lipsitz LA, Mietus J, Moody GB, Goldberger AL. Spectral characteristics of heart rate variability before and during postural tilt: relations to aging and risk of syncope. Circulation 1990; 81:1803–1810. 4. Yu S, Katoh T, Makino H, et al. Age and heart rate variability after soccer games. Res Sports Med 2010; 18:263–269. 5. Acharya UR, Joseph KP, Kannathal N, et al. Heart rate variability: a review. Med Biol Eng Comput 2006; 44:1031–1051. J Travel Med 2014; 21: 159–162
162 6. Lu W, Kuo C. Comparison of the effects of Tai Chi Chuan and Wai Tan Kung exercises on autonomic nervous system modulation and on hemodynamics in elder adults. Am J Chin Med 2006; 34:959–968. 7. Lim YH, Kim H, Kim JH, et al. Effect of diurnal temperature range on cardiovascular markers in the elderly in Seoul, Korea. Int J Biometeorol 2013; 57: 597–603. 8. Holguin F, T´ellez-Rojo MM, Lazo M, et al. Cardiac autonomic changes associated with fish oil vs soy oil supplementation in the elderly. Chest 2005; 127:1102–1107. 9. Wolk R, Gami AS, Garcia-Touchard A, Somers VK. Sleep and cardiovascular disease. Curr Probl Cardiol 2005; 30:625–662. 10. Cacioppo JT, Berntson GG, Malarkey WB, et al. Autonomic, neuroendocrine, and immune responses to psychological stress: the reactivity hypothesis. Ann N Y Acad Sci 1998; 840:664–673. 11. Lee I. Autonomic nervous system dysfunction. Taipei: Hao Wen Co., Ltd., 1997. 12. Kuo Y. Improving autonomic nervous system function. Taipei: Persimmonbooks, 2012. 13. Strauss-Blasche G, Riedmann B, Schobersberger W, et al. Vacation at moderate and low altitude improves perceived health in individuals with metabolic syndrome. J Travel Med 2004; 11:300–306. 14. Fredmana P, Tyrv¨ainenbc L. Frontiers in nature-based tourism. Scand J Hosp Tour 2010; 10:177–189.
J Travel Med 2014; 21: 159–162
Chang 15. Arnegger J, Woltering M, Job H. Toward a productbased typology for nature-based tourism: a conceptual framework. J Sustain Tour 2010; 18:915–928. 16. Eaker ED, Pinsky J, Castelli WP. Myocardial infarction and coronary death among women: psychosocial predictors from a 20-year follow-up of women in the Framingham study. Am J Epidemiol 1992; 135:854–864. 17. Gump BB, Matthews KA. Are vacations good for your health? The 9-year mortality experience after the multiple risk factor intervention trial. Psychosom Med 2000; 62:608–612. 18. Strauss-Blasche G, Reithofer B, Schobersberger W, et al. Effect of vacation on health: moderating factors of vacation outcome. J Travel Med 2005; 12:94–101. 19. de Bloom J, Geurts SA, Sonnentag S, et al. How does a vacation from work affect employee health and well-being? Psychol Health 2011; 26:1606–1622. 20. Bowler DE, Buyung-Ali LM, Knight TM, Pullin AS. A systematic review of evidence for the added benefits to health of exposure to natural environments. BMC Public Health 2010; 10:456. 21. Berto R. Assessing the restorative value of the environment: a study on the elderly in comparison with young adults and adolescents. Int J Psychol 2007; 42:331–341. 22. Huang F, Chien D, Chung U. Effects of Hatha yoga on stress in middle-aged women. J Nurs Res 2013; 21:59–66. 23. Kutner MH, Nachtsheim CJ, Neter J, Li W. Applied linear statistical models. New York: McGraw-Hill, 2005.
