Study Shows Forest Exposure Boosts Immune Function and Anti-Cancer Activity

Reduce Stress Hormones 21% with this Forest Therapy

Author

Hector Caraballo, MD
November 04, 2023

Dear Health Quest Newsletter readers, 

I am summarizing an interesting research article I recently came across on the health benefits of spending time in forest environments. The study, conducted in Japan, found that being in forest settings can have measurable positive impacts on our physiological and psychological well-being compared to being in urban environments. 

Specifically, after people spent time walking or viewing forests, they showed decreases in blood pressure, pulse rate, and stress hormone levels. They also showed increased activity in the parasympathetic nervous system, our rest and relaxation system. Psychologically, people reported decreased feelings of anger, fatigue, tension, depression, and confusion after forest exposure. They also felt increased vigor. 

The researchers suggest a few reasons why this effect occurs. First, as human beings evolved in natural settings, our bodies are adapted to that environment and find it more relaxing. Also, physical factors like the lower light, humidity, and air pressure in forests contribute to the calming effect. 

Whatever the causes, it's fascinating that something as simple and accessible as a walk in the woods can provide tangible health benefits. While more research is still needed, forest therapy could help with stress management and the prevention of stress-related illnesses. It's a reminder for us all to take advantage of opportunities to connect with nature, even for short periods of time. A little bit of forest bathing could be just what the doctor ordered!

Let me know if you have any other thoughts or reactions to this research. I'm happy to chat more about the health effects of our environment.

Warm regards,

Hector Caraballo, MD

Here are the key takeaway and summary of the article:

Key Takeaway

Forest environments can have physiological and psychological health benefits, including lowering cortisol, blood pressure, pulse rate, and sympathetic nervous system activity while increasing parasympathetic nervous system activity. These effects can help reduce stress and promote relaxation.  

Summary

- This paper reviews research on the physiological effects of "Shinrin-yoku" or forest bathing in Japan. 

- Field experiments were conducted in 24 forest sites with 280 total subjects. Measurements included salivary cortisol, pulse rate, blood pressure, heart rate variability, and psychological mood.

- Results showed that compared to city environments, forest environments significantly decreased cortisol, pulse rate, blood pressure, and sympathetic nervous system activity and increased parasympathetic nervous activity. 

- Psychological effects included decreased tension, depression, anger, fatigue, confusion, and increased vigor after viewing or walking in forests versus cities.

- The physical factors of forests, like illumination, humidity, and pressure, were correlated with positive psychological effects.  

- The relaxation and stress reduction effects were attributed to humans' evolutionary adaptation to natural environments.

- The findings support the development of forest therapy for stress management and preventive medicine. More research is needed on other natural environments like grasslands and watersides.

FAQ’s

What effect did forest bathing have on natural killer cells?

The article mentioned a few studies that found the effects of forest environments on natural killer (NK) cells, a type of white blood cell involved in immune function. Specifically:

- A study by Li et al. showed that forest bathing trips enhanced human NK activity and expression of anti-cancer proteins in both male and female subjects. 

- Another study by Li et al. found that visiting a forest but not a city increased NK activity and anti-cancer protein expression. 

- The article states high cortisol levels can correspond to lower NK activity. The decreases in cortisol seen after forest exposure may help increase NK activity.

- The authors suggest the changes in NK activity and anti-cancer proteins indicate forest environments can aid the recovery of immune system function.

In summary, the referenced studies found spending time in forests could increase NK cells and proteins involved in immune defense against cancer. The article hypothesized this may be one mechanism behind the relaxing effects of forest bathing.

What are natural killer cells, and why are they important to our immune system?

Natural killer (NK) cells are a type of lymphocyte - a variety of white blood cell that is part of the immune system. NK cells play an important role in the innate immune system and in defending against viruses and cancer. Specifically:

- NK cells can directly identify and kill infected or cancerous cells by releasing cytotoxic granules that induce apoptosis. This is known as their cytotoxic activity.

- NK cells also release cytokines that communicate with and stimulate other immune cells like T cells and macrophages, coordinating a broader immune response. 

- NK cells contribute to rapid immune reactions against pathogens and tumors in the early stages before antibodies are made.

- Lower NK cell cytotoxicity has been linked to increased cancer risk and viral infections.

In summary, NK cells are a critical component of the innate immune system and form an early defense against viruses and cancerous changes in the body. Their ability to directly kill abnormal cells and communicate with other immune players makes them essential for immune surveillance and activation. Factors that increase NK cell number and activity are believed to support immune system health.

Source:

Park, B.J., Tsunetsugu, Y., Kasetani, T., Kagawa, T. and Miyazaki, Y., 2010. The physiological effects of Shinrin-yoku (taking in the forest atmosphere or forest bathing): Evidence from field experiments in 24 forests across Japan. Environmental Health and Preventive Medicine, 15(1), pp.18-26.