In 2010, HPHP Central reported on the research of Dr Qing Li, which demonstrated that the Japanese practice of ‘forest bathing’ reduced stress levels and could even help fight cancer. In this update on Dr Li’s latest work, we examine his latest research findings that show that spending time in forest environments, also known as national parks and protected areas in other countries, has even more benefits than previously envisioned.

Walking has long been promoted as an activity beneficial to human health: an accessible, free, and easy way to develop fitness that is suitable for people of all ages. It’s been advocated as an aid in the prevention and control of modern diseases such as obesity and diabetes, as well as being useful in the treatment of mental health conditions such as depression.

Not All Walking Is Equal: Prior Findings

Although attention has been given to the overall benefits derived from walking activities, far less research has been done on distinguishing between various sorts of walking and the diverse impacts they may deliver. However Dr Qing Li, in his groundbreaking research in 2010, analysed the effects of spending time in forest environments on mood, immune function and stress levels. His findings showed that immune function improved, with the number of NK (cancer-fighting) cells elevated after a three-day forest walking trip, and remaining elevated for up to 30 days afterwards. He also found that levels of anxiety, depression and anger were lowered by the forest bathing, with a reduction in stress hormone levels. This led him to conclude that the risk of psycho-social stress-related diseases is decreased by time spent walking in forest environments.

Investigating Forest Walking and Heart Health

Dr Li hypothesised that, given the documented reductions in stress levels, walking in forests might also help with blood pressure and cardiovascular function. Therefore, in his latest research Dr Li and his colleagues from the Department of Hygiene and Public Health at the Nippon Medical School investigated the effects of walking on cardiovascular and metabolic health as determined through blood and urine tests and by measuring blood pressure.

In this study, he used 16 healthy male subjects who took part in two separate walking trips: one took place in an urban area of Tokyo and the other was conducted a week later in a forested area. The temperatures and humidity levels on both trips were within the same range. Both trips involved walking for the same amount of time: two hours in the morning and two hours in the afternoon. Each walk covered the same distance. The subjects ranged in age from 36 to 77 years of age and consumed the same amount of calories on each trip. No alcohol was consumed during the study period.

Investigating Forest Walking: Results

The complete findings of Dr Li’s research were published in the European Journal of Applied Physiology (2011) 111: 2845-2853.

The results were emphatic in demonstrating the benefits of walking in forest environments. Dr Li found that both systolic and diastolic blood pressure was reduced by walking in the forest park, but not by walking in the urban area. This is extremely significant given that there was no difference in the levels of physical activity on the two trips and the subjects were generally middle-age with higher baseline blood pressure levels than previous subjects in other blood pressure studies.

To determine why this lowered blood pressure was observed, Dr Li measured the levels of urinary adrenaline and noradrenaline, which he says have significant correlations with blood pressure. The levels of both tended to decrease after walking in the forest whereas walking in the urban area did not affect them. He concluded that walking in forests lowers the activity of the sympathetic nerve and increases the activity in the parasympathetic nerve.

He also measured adiponectin, which is a hormone that, when its levels are lower than normal, is associated with several disorders including diabetes and cardiovascular disease. He found that walking in the forest, but not the urban area, lifted the level of adiponectin in the blood.

The levels of DHEA-S, which is a secretory product of the adrenal gland, were also measured. DHEA-S generally declines with age and is indicative of the onset of degenerative diseases. Walking in forests increased the level of DHEA-S in the blood whereas the increase recorded after the urban walk was not statistically significant.

Finally, Dr Li measured NT-proBNP which is a cardiac biomarker used in assessing heart failure. Moderate levels of physical activity have been reported to lower NT-proBNP, so Dr Li measured the average number of steps taken by the subjects in the study. On the day before walking, the average number of steps taken was 5951. On day of the trip, this rose to an average of 17,156 steps. After the trip, NT-proBNP concentrations decreased significantly and remained at the lower level for over a week. This change was independent of blood pressure. (It should be noted that participating in an intense activity, such as running a marathon, raises NT-proBNP.)

Not All Walking Is Equal: Conclusion

Why is walking in a forest different from walking in an urban area? We all instinctively feel that the sense of well-being that comes from spending time in a natural environment, with the spectacular scenery, sounds and sights of the outdoors, is a totally different experience from walking in our suburban streets. Dr Li asked this question during the course of his research too and his findings implicate our sense of smell as well. They suggest that the natural fragrance of trees, known as phytoncides, contributed to the reduction in blood pressure observed during the forest walking.

In conclusion, walking in forest environments, already reported to have beneficial effects on immune system function and stress levels, can also be beneficial to heart health and blood pressure. Further, engaging in the same amount of walking activity in an urban environment does not produce the cardiovascular improvements that are delivered by walking in a forested environment. These findings have major implications for how we view exercise and its place in the modern urbanised world. They also invite further research into the long-term effects of exposure to forest areas.

Dr Qing Li is Vice President of the International Society of Nature and Forest Medicine (INFOM). He is also President of the Japanese Society of Forest Medicine, and Senior Assistant Professor at the Nippon Medical School in Tokyo, Japan. His book Forest Medicine has recently been published by Nova Publishers (ISBN 9781614709824).