The location where we exercise may have a significant impact on our body’s immune response, according to emerging research. Forests are increasingly recognized not simply as places for recreation, but as environments that simultaneously support physical recovery and stress reduction.
A study conducted by Hiroko Ochiai and her team at the Tokyo Medical Center of the National Hospital Organization (NHO) in Japan, published in in the journal Scientific Reports, investigated the effects of walking in forests versus urban environments on the immune systems of healthy men aged 40-70. The randomized controlled trial involved 78 participants, and found that the forest group exhibited significantly higher levels of secretory immunoglobulin A (sIgA), a key indicator of respiratory mucosal immunity, compared to the urban group. The difference in adjusted means was 32.1µg/mL (p=0.035).
Just 90 Minutes of Forest Walking Can Make a Difference
This finding suggests that even short periods of activity in natural settings can boost the body’s antibody response, contributing to enhanced defense against pathogens. However, researchers caution that the study population was limited to middle-aged and older men, and the results may not be generalizable to other age groups or women.
sIgA is a primary antibody found in the mucous membranes of the mouth, nose, and bronchial tubes, where it prevents pathogens from attaching to the body. The study indicates that even a brief period of activity can increase levels of this crucial immune component.
Stress Hormones Also Reduced
The forest environment also led to a greater reduction in cortisol, the stress hormone, compared to the urban setting. Participants in the forest group also reported lower scores for tension, anxiety, and fatigue. This demonstrates that physiological responses can vary depending on the environment, even when exercise intensity is the same. Research increasingly supports the concept of “green exercise”—physical activity in natural environments—as a means of promoting autonomic nervous system stability and psychological relaxation.
Temperature and Humidity Play a Role
Exercise effectiveness can be more strongly influenced by environmental conditions like temperature and humidity than by altitude. Higher altitudes can lead to lower oxygen levels, increasing heart rate and exercise intensity, which may be burdensome depending on an individual’s health status. For most people, exercising at a moderate altitude with a comfortable temperature and humidity level is advisable.
Natural Environment Activity Drives the Effect
Regular physical activity is essential for maintaining health. While forests provide an optimal environment for enhancing exercise benefits, consistency is key to maximizing those benefits. Making a habit of visiting nearby natural spaces is a practical first step.
[Frequently Asked Questions]
Q1. How often should I do this to see benefits?
A1. This research showed changes in immune markers and stress hormones after just a single 90-minute session. However, the duration of these effects remains unknown. Experts recommend engaging in regular exercise in natural environments at least 1-2 times per week.
Q2. Would a city park have a similar effect?
A2. While urban routes may have trees planted at intervals, they differed in sIgA levels from forests with a diverse range of species. Even if a completely natural forest environment isn’t accessible, parks with a high proportion of green space and low noise levels can offer psychological restorative benefits.
Q3. If it’s good for immunity, will it help prevent colds?
A3. SIgA is an antibody that blocks pathogens from entering the respiratory tract, so higher levels may increase resistance to viral infections. However, it’s not yet clear whether increased sIgA levels directly translate to a reduction in cold incidence. Immunity is influenced by multiple factors, including sleep, nutrition, and stress levels, so it’s difficult to attribute preventative effects solely to activity in natural environments.
Time spent in nature offers a compelling and accessible pathway to improved health and well-being. While further research is needed to fully understand the mechanisms at play and to determine the optimal “dose” of nature exposure, the evidence increasingly suggests that incorporating forest bathing or simply spending time in green spaces can be a valuable component of a healthy lifestyle.
