Time in Nature or Forest Bathing

Our assessments of evidence for each medical benefit fall into one of these categories:

• Strong evidence: consistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analysesa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results
• Good evidence: significant effects in one large or several mid-sized and well-designed clinical studies ( randomized controlled trialsa study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects with an appropriate placebo or other strong comparison control or observational studies that control for confounds)
• Modest evidence: significant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies), or several small studies aggregated into a meta-analysis
• Preliminary evidence: significant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect
• Weak evidence: one or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects
• Insufficient evidence: preclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example)

• Less anxiety among people with cancer in an educational facility with outlooks on natural scenery compared to no natural scenery in a small observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁶Emami E, Amini R, Motalebi G. The effect of nature as positive distractibility on the healing process of patients with cancer in therapeutic settings. Complementary Therapies in Clinical Practice. 2018 Aug;32:70-73.

• About two-thirds of people with cancer responding to a survey agreed that nature or listening to ‘natural music’ (birdsong and the wind) “helped them feel significantly better during or after illness” and agreed that “to walk or engage in any activity outdoors gives you a spiritual sense” in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods (survey) study⁷Ahmadi F, Ahmadi N. Nature as the most important coping strategy among cancer patients: a Swedish survey. Journal of Religion and Health. 2015 Aug;54(4):1177-90.

• Better sleep efficiency and sleep time among people with gastrointestinal tract cancer participating in forest therapy for 6 days compared to baseline in a small uncontrolled triala study in which a therapy is used, but without a comparison group against which to judge outcomes; an uncontrolled trial is considered a weak study design⁸Kim H, Lee YW, Ju HJ, Jang BJ, Kim YI. An exploratory study on the effects of forest therapy on sleep quality in patients with gastrointestinal tract cancers. International Journal of Environmental Research and Public Health. 2019 Jul 10;16(14):2449.

Time in nature with adventure social support: weak evidence of better quality of life among people with cancer participating in time in nature with social support

• Better health-related quality of life in themes of developing connections, togetherness, rebuilding self-esteem, and creating memories among adolescents with cancer participating in an adventure therapy program in a remote area of Canada compared to baseline in a small uncontrolled triala study in which a therapy is used, but without a comparison group against which to judge outcomes; an uncontrolled trial is considered a weak study design⁹Stevens B, Kagan S et al. Adventure therapy for adolescents with cancer. Pediatric Blood & Cancer. 2004 Sep;43(3):278-84. our note: we consider this combination therapy because time in nature was combined with social support, which was prominent in the themes the youth mentioned

Time in nature with horticultural therapy, yoga meditation, and support group therapy: weak evidence of lower cancer-associated fatigue, and better quality of life, functional well-being, and spiritual well-being among people with cancer participating in forest therapy, horticultural therapy, yoga meditation, and support group therapy

• Lower cancer-associated fatigue, and better quality of life, functional well-being, and spiritual well-being among people with cancer participating in forest therapy, horticultural therapy, yoga meditation, and support group therapy for 12 weeks compared to baseline in a small uncontrolled study¹⁰Nakau M, Imanishi J et al. Spiritual care of cancer patients by integrated medicine in urban green space: a pilot study. Explore (NY). 2013 Mar-Apr;9(2):87-90.

Anxiety

Modest evidence of lower anxiety among people participating in forest bathing or spending time in a forest

Modest evidence of less anxiety and agitation among people without cancer in critical care listening to recordings of nature-based sounds

Preliminary evidence of less use of psychotropic drugs for anxiety among people in urban areas visiting natural spaces, although no evidence of an effect of living near or having views of green and blue (terrestrial and water) spaces

• Lower anxiety among children and/or adults participating in forest bathing in a systematic review of systematic reviews and meta-analysesa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of moderate and low quality¹¹Stier-Jarmer M, Throner V et al. The psychological and physical effects of forests on human health: a systematic review of systematic reviews and meta-analyses. International Journal of Environmental Research and Public Health. 2021 Feb 11;18(4):1770.
• Lower anxiety among people after time in a forest, whether following the forest bathing model or not, compared to time in urban settings or indoors in a review of 9 controlled trialsa study design in which people are assigned to either an experimental group or a control group to compare the outcomes from different treatment; assignment is not random, and so this is not as strong a study design as a randomized controlled trial, but still stronger than an uncontrolled trial¹²Farrow MR, Washburn K. A review of field experiments on the effect of forest bathing on anxiety and heart rate variability. Global Advances in Health and Medicine. 2019 May 16;8:2164956119848654.
• Lower anxiety among adults suffering from pre-hypertension or hypertension participating in forest bathing in a review of 14 controlled and uncontrolled trialsa study in which a therapy is used, but without a comparison group against which to judge outcomes; an uncontrolled trial is considered a weak study design of moderate quality¹³Yau KK, Loke AY. Effects of forest bathing on pre-hypertensive and hypertensive adults: a review of the literature. Environmental Health and Preventive Medicine. 2020 Jun 22;25(1):23.
• Less anxiety and agitation among coronary artery bypass graft patients and/or patients on mechanical ventilator support listening to recordings of nature-based sounds compared to other people in a systematic review including 4 small RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹⁴Thrane SE, Hsieh K et al. Could complementary health approaches improve the symptom experience and outcomes of critically ill adults? A systematic review of randomized controlled trials. Complementary Therapies in Medicine. 2019 Dec;47:102166.
• Less use of psychotropic drugs (anxiolytics, hypnotics, and antidepressants) among people in urban areas visiting natural spaces at least 3 times a week compared to less than once a week, although no evidence of an effect of living near or having views of green and blue (terrestrial and water) spaces in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods¹⁵Turunen AW, Halonen J et al. Cross-sectional associations of different types of nature exposure with psychotropic, antihypertensive and asthma medication. Occupational & Environmental Medicine. 2023 Feb;80(2):111-118.

Cardiovascular symptoms

Modest evidence of lower blood pressure or heart rate among people with more exposure to nature

Preliminary evidence of lower blood pressure among people without cancer on mechanical ventilator support listening to recordings of nature-based sounds

• Lower blood pressure among healthy people exposed to more neighborhood green space, access to green space, or time spent in forests or other natural environments compared to less in a meta-analysis of 12 controlled trials¹⁶Twohig-Bennett C, Jones A. The health benefits of the great outdoors: a systematic review and meta-analysis of greenspace exposure and health outcomes. Environmental Research. 2018;166:628–637.
• Lower heart rate among healthy people exposed to more neighborhood green space, access to green space, or time spent in forests or other natural environments compared to less in a meta-analysis of 10 controlled trials¹⁷Twohig-Bennett C, Jones A. The health benefits of the great outdoors: a systematic review and meta-analysis of greenspace exposure and health outcomes. Environmental Research. 2018;166:628–637.
• Lower blood pressure—both systolic and diastolic—among people on mechanical ventilator support listening to nature-based sounds compared to those not listening to recordings of nature-based sounds in a small RCT¹⁸Tadrisi SD, Zayeri F, Vaismoradi M, Jasper M. Effect of nature-based sounds’ intervention on agitation, anxiety, and stress in patients under mechanical ventilator support: a randomised controlled trial. International Journal of Nursing Studies. 2013 Jul;50(7):895-904.

Cognitive difficulties

Modest evidence of better cognitive performance among people listening to nature-based sounds

• Better cognitive performance among people listening to nature-based sounds compared to other people in a meta-analysis of 36 experimental or observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁹Buxton RT, Pearson AL, Allou C, Fristrup K, Wittemyer G. A synthesis of health benefits of natural sounds and their distribution in national parks. Proceedings of the National Academy of Sciences of the United States of America. 2021 Apr 6;118(14):e2013097118.

Depression or mood

Modest evidence of better mood among people listening to nature-based sounds

Preliminary evidence of lower risk of depression among people with more day-to-day exposure to nature (green space)

Preliminary evidence of lower depression scores among people participating in forest therapy

Preliminary evidence of less use of psychotropic drugs for depression among people in urban areas visiting natural spaces, although no evidence of an effect of living near or having views of green and blue (terrestrial and water) spaces

• Better mood among people listening to nature-based sounds compared to other people in a meta-analysis of 36 experimental or observational studies²⁰Buxton RT, Pearson AL, Allou C, Fristrup K, Wittemyer G. A synthesis of health benefits of natural sounds and their distribution in national parks. Proceedings of the National Academy of Sciences of the United States of America. 2021 Apr 6;118(14):e2013097118.
• Higher risk of developing single and recurrent depressive disorder or a mood disorder among people with less dense vegetation near their residences compared to those with more dense vegetation near their residences in a very large observational study²¹Engemann K, Pedersen CB et al. Residential green space in childhood is associated with lower risk of psychiatric disorders from adolescence into adulthood. Proceedings of the National Academy of Sciences. 2019 Mar 12;116(11):5188-5193.
• A small decrease in depression scores among adults participating in forest bathing, particularly among adults with health problems and those actively participating and involved with nature, in systematic review of 28 clinical trials of quality from low to high²²Lee I, Choi H, Bang KS, Kim S, Song M, Lee B. Effects of forest therapy on depressive symptoms among adults: a systematic review. International Journal of  Environmental Research and Public Health. 2017 Mar 20;14(3):321. and a meta-analysis of 6 RCTs of low quality²³Kotera Y, Richardson M, Sheffield D. Effects of shinrin-yoku (forest bathing) and nature therapy on mental health: a systematic review and meta-analysis. International Journal of Mental Health and Addiction. 2022 20:337–361.
• Less use of psychotropic drugs for depression among people in urban areas visiting natural spaces at least 3 times a week compared to less than once a week, although no evidence of an effect of living near or having views of green and blue (terrestrial and water) spaces in a large observational study²⁴Turunen AW, Halonen J et al. Cross-sectional associations of different types of nature exposure with psychotropic, antihypertensive and asthma medication. Occupational & Environmental Medicine. 2023 Feb;80(2):111-118.

Pain

Modest evidence of less pain among people listening to recordings of nature-based sounds

• Less pain among people listening to nature-based sounds compared to other people in a meta-analysis of 36 experimental or observational studies²⁵Buxton RT, Pearson AL, Allou C, Fristrup K, Wittemyer G. A synthesis of health benefits of natural sounds and their distribution in national parks. Proceedings of the National Academy of Sciences of the United States of America. 2021 Apr 6;118(14):e2013097118.
• Less pain among coronary artery bypass graft patients and/or patients on mechanical ventilator support listening to recordings of nature-based sounds compared to other people in a systematic review including 4 small RCTs²⁶Thrane SE, Hsieh K et al. Could complementary health approaches improve the symptom experience and outcomes of critically ill adults? A systematic review of randomized controlled trials. Complementary Therapies in Medicine. 2019 Dec;47:102166.

Quality of life, health and well-being

Modest evidence of better reported health and well-being among people with exposure to nature

• 59% greater likelihood of self-reported good health and 23% greater likelihood of self-reported high well-being among people, including older adults and people with health issues, with 200 to 300 minutes of recreational nature contact in the past week compared to other people in a very large observational study²⁷White MP, Alcock I et al. Spending at least 120 minutes a week in nature is associated with good health and wellbeing. Scientific Reports. 2019 Jun 13;9(1):7730.

Sleep disruption

Preliminary evidence of better sleep quality and quantity among people with more exposure to nature (green space)

• Weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward better sleep quality and quantity among people with more exposure to green space compared to those with less exposure, with some people also exercising or working in green space or gardening, in a systematic review of 13 interventional and observational studies²⁸Shin JC, Parab KV, An R, Grigsby-Toussaint DS. Greenspace exposure and sleep: a systematic review. Environmental Research. 2020 Mar;182:109081.

Stress

Modest evidence of lower risk of stress-related disorders among people with dense vegetation near their residences

Modest evidence of less stress and annoyance among people listening to nature-based sounds

Preliminary evidence of lower perceived stress, particularly in the frequency of anger, among preschool children participating in a structured nature-related program

• Higher risk of developing neurotic and stress-related disorders among people with less dense vegetation near their residences compared to more dense vegetation in a very large observational study²⁹Engemann K, Pedersen CB et al. Residential green space in childhood is associated with lower risk of psychiatric disorders from adolescence into adulthood. Proceedings of the National Academy of Sciences. 2019 Mar 12;116(11):5188-5193.
• Less stress and annoyance among people listening to nature-based sounds compared to other people in a meta-analysis of 36 experimental or observational studies³⁰Buxton RT, Pearson AL, Allou C, Fristrup K, Wittemyer G. A synthesis of health benefits of natural sounds and their distribution in national parks. Proceedings of the National Academy of Sciences of the United States of America. 2021 Apr 6;118(14):e2013097118.
• Lower perceived stress, particularly in the frequency of anger, among preschool children participating in a 10-week structured nature-related “Play&Grow” program compared to controls in a small RCT³¹Sobko T, Liang S, Cheng WHG, Tun HM. Impact of outdoor nature-related activities on gut microbiota, fecal serotonin, and perceived stress in preschool children: the Play&Grow randomized controlled trial. Scientific Reports. 2020 Dec 15;10(1):21993.

Other symptoms and side effects

Recovery from surgery: preliminary evidence of shorter hospital stays after surgery, better evaluations, and less analgesic use among people in hospital rooms with a view of natural scenes

• Shorter hospital stays after surgery, fewer negative evaluative comments in nurses’ notes (possibly indicating better mood), and fewer potent analgesics among people in hospital rooms with windows looking out on a natural scene compared to rooms facing a brick building wall in a small controlled study³²Ulrich RS. View through a window may influence recovery from surgery. Science. 1984;224(4647):420‐421.

Time in nature in combination with other therapies

Time in nature (outdoor walking) with light exposure and several vitamins: preliminary evidence of higher measures of overall mood, self-esteem, and general sense of well-being and fewer symptoms on two measures of depression among women with symptoms of mild to moderate depression not taking any mood-altering medication and treated with a brisk 20-minute outdoor walk, increased light exposure throughout the day, and a vitamin regimen

• Higher measures of overall mood, self-esteem, and general sense of well-being and fewer symptoms on two measures of depression among women with symptoms of mild to moderate depression not taking any mood-altering medication and treated with a brisk 20-minute outdoor walk at target heart rate of 60% of maximum heart rate, increased light exposure throughout the day, and a vitamin regimen of 50 mg vitamin B1 (thiamine), 50 mg vitamin B6 (pyroxidine), 50 mg vitamin B2 (riboflavin), 400 mcg folic acid, 200 mcg selenium, and 400 IU vitamin D compared to a placebo vitamin in a mid-sized RCT³³Brown MA, Goldstein-Shirley J, Robinson J, Casey S. The effects of a multi-modal intervention trial of light, exercise, and vitamins on women’s mood. Women Health. 2001;34(3):93-112.

• Lower cancer mortality over 8 years among women living near higher levels of vegetation compared to the lowest level in a very large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study³⁴James P, Hart JE, Banay RF, Laden F. Exposure to greenness and mortality in a nationwide prospective cohort study of women. Environmental Health Perspectives. 2016 Sep;124(9):1344-52.

• Lower risk of breast cancer among people living in urban areas close to green space compared to distant from green space in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study³⁵O’Callaghan-Gordo C, Kogevinas M et al. Residential proximity to green spaces and breast cancer risk: the multicase-control study in Spain (MCC-Spain). International Journal of Hygiene and Environmental Health. 2018 Sep;221(8):1097-1106.

• Lower risk of childhood leukemia among children living in a large urban area within 250 m of an urban parks or urban wooded areas compared to greater distances in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study³⁶Ojeda Sánchez C, Segú-Tell J et al. Urban green spaces and childhood leukemia incidence: a population-based case-control study in Madrid. Environmental Research. 2021 Nov;202:111723.

• Lower risk of prostate cancer among people with higher levels of residential greenness, either recently or about a decade earlier, in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study³⁷Demoury C, Thierry B et al. Residential greenness and risk of prostate cancer: a case-control study in Montreal, Canada. Environment International. 2017 Jan;98:129-136.