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Chapter 10 of the book

Green and Quiet

ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.3 things to start with2 popular claims graded43 works cited

How the chapter opens

In 2002 a metallic green beetle from East Asia was identified as the reason ash trees were dying in Detroit and in Windsor, Ontario. The emerald ash borer kills virtually every North American ash it infests. Within a decade it had killed roughly a hundred million American trees.

Geoffrey Donovan, an economist with the US Forest Service, saw something in the destruction that researchers almost never get: an experiment run by chance. Nobody could decide which counties lost their trees, or when. The beetle spread in an order that owed much to where somebody's firewood happened to travel. So Donovan's team compared adult deaths county by county across fifteen states, allowing for who lived there and when the beetle arrived.

What the chapter covers

The argument, the studies and the stories are in the book. Get the book.

  • ·What Your Body Expects
  • ·What It Gets Instead: Less Green
  • ·What It Gets Instead: Noise That Never Stops
  • ·What It Gets Instead: Loud, and the Ear That Wears

Mismatch card

The system

The stress system, attention and the heart, tuned by a living landscape; hearing, and the threat circuit it feeds.

What it expects

Daylight hours among plants, water and animals, and a quiet natural background broken by occasional sounds worth noticing.

What it gets

Most of life indoors, a view of a wall, and mechanical noise that never stops, including at night, with bursts loud enough to damage the ear.

What happens in the gap

Slower stress recovery, more psychiatric diagnoses among children raised in the least green places, extra heart and lung deaths where the trees go, broken sleep, and avoidable hearing loss on a population scale.

The handrail

Two hours a week somewhere green, the arm's-length test for loud noise, a quiet bedroom, and a hearing test if conversation gets harder or once you are past 50 (ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.)

Strength of evidence

ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials. Natural experiments, twin and mover designs and a randomized trial point the same way for green space, but individual effects are modest; noise exposure limits are solid, the noise-and-heart link is observational, and hearing aids have not been shown to prevent dementia.

What you've heard

Popular claims this chapter tests, each with the book's verdict and grade.

The protocol

Each action carries the book's evidence grade. How the grades work.

Start here

  1. Spend about two hours a week somewhere green, including city parks

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

    How: four half-hour visits, or one long weekend walk, in any park, riverside, woodland or beach. Why: in a large English survey the benefit started around two hours, though a survey cannot prove direction.

  2. Protect your hearing from loud noise

    StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.for the exposure limits

    How: use the arm's-length test. If you must raise your voice to talk to someone beside you, keep the time short, step away from the speakers, or wear earplugs; at concert volumes the safe daily allowance runs out within an hour. With headphones, keep the volume low enough to hear someone next to you. Why: noise damage to hearing is permanent and avoidable.

  3. Get a hearing test if you are over 50 or struggling to follow conversation

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.for hearingnot graded for dementia

    How: ask your doctor or an audiologist, and mention any ringing. One warning sign the Food and Drug Administration lists: "You find it hard to follow speech in groups." In the United States, hearing aids for perceived mild to moderate loss have been sold over the counter since 2022, without a prescription or exam. Why: hearing loss is common, undertreated and easy to miss in yourself; no age is backed by a trial, and 50 is simply a sensible point to stop guessing.16

Then, pick from this menu

  • **Make each visit twenty to thirty minutes if you can; ten still registers (EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.).** Leave the phone in your pocket, as the cortisol study's volunteers did. A daily stretch of real quiet is for rest, not a proven treatment.

  • **Guard your sleep from traffic noise (ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials. that night noise disturbs sleep; EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested. for any single fix).** Sleep on the quiet side of the home if you have a choice, keep the bedroom window closed on the traffic side, and try foam earplugs, fitted as the packet shows. If a closed window makes the room too hot, a fan keeps the air moving (Chapter 9). None of these has been tested against health outcomes; they are cheap and low-risk.

  • **If your mood is low, join something structured outdoors for eight to twelve weeks (ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.).** Walking groups, gardening projects or conservation volunteering. Pooled randomized trials found better mood and less anxiety, with sessions of twenty to ninety minutes working best. This complements treatment for depression or anxiety; never stop a prescribed treatment for a walk.17

  • **For your street, plant trees and green empty lots (ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.).** How: join a local tree-planting group like the Portland nonprofit in the opening, or ask your city about street-tree and vacant-lot programs. Why: this is the one recommendation backed by natural experiments and a citywide randomized trial, and the only one that helps people who never read the advice.

If this is you

Night shifts

protect daytime sleep first: earplugs, the quietest room, the same slot every workday (Chapter 8). Take your green time on the way home or on days off.

With young children

count family park time toward your two hours. The Danish link was about where children live, not day trips, so treat outings as a bonus. Children's ears are more vulnerable than adults' at lower levels. If you use a white-noise machine in a nursery, keep it low and well away from the crib: measured machines at full volume exceeded safe levels at close range (ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.).18

Over 50, or stiff joints

a flat park loop or a bench by water counts; sitting in green still registered in studies. Book the hearing test now rather than waiting until conversation gets hard.

Tight budget

parks, riversides and tree-lined streets are free, and foam earplugs cost little.

Short on time

split the two hours into ten- or twenty-minute pieces: a lunch break under trees, a walk after dinner, part of the commute on foot.

Tinnitus

about one adult in seven has it, and you are not imagining it. Raise it with your doctor or at your hearing test, and use the arm's-length test.

Safety

Ticks live in grassy, brushy and wooded areas. The Centers for Disease Control and Prevention advises a registered insect repellent, permethrin-treated clothing, a full-body check when you get home and a shower soon after.19 Sun (Chapter 7) and heat (Chapter 9) apply outdoors. None of this replaces treatment for depression, anxiety or hearing loss.

The skeptic's box

What could overturn this chapter, from the chapter itself.

The central objection never goes away: healthier, wealthier people live in greener places and visit parks more, and the designs built to beat it only half succeed. Identical twins kept the depression link but lost stress and anxiety, and in Denmark, adjustment shrank the excess risk of ADHD by nearly two-thirds; the authors wrote that their estimates "fundamentally only show correlations." Exposure is crude, too: most studies use a satellite greenness score that cannot tell a grand elm from a weedy verge, and across the largest US cities, the greener ones had higher death rates, blamed partly on sprawl and driving. In Berlin, volunteers randomly sent on an hour's walk in a forest showed calmer activity in the brain's threat center than those sent down a shopping street, yet their felt and measured stress did not differ.20

On noise, the heart findings are observational, and people beside the loudest roads differ in more ways than decibels. On hearing and dementia, early dementia can itself make hearing worse, and damage to blood vessels could harm both ear and brain separately.

Go deeper in the reference library

The research this chapter was built from, as longer reference entries: each with its own mismatch card, graded recommendations and the case against it.

See also in the book

Sources behind this page

  1. 20.Thygesen, M., Engemann, K., Holst, G.J., Hansen, B., et al. (2020). "The association between residential green space in childhood and development of attention deficit hyperactivity disorder: a population-based cohort study." Environmental Health Perspectives, 128(12), 127011. https://doi.org/10.1289/EHP6729 (IRR 1.55 before and 1.20 after adjustment; quotation from Engemann et al. 2019, note 4.) ; Donovan, G.H., Gatziolis, D., Derrien, M., Michael, Y.L., et al. (2022). "Shortcomings of the normalized difference vegetation index as an exposure metric." Nature Plants, 8(6), 617-622. https://doi.org/10.1038/s41477-022-01170-6 ; Richardson, E.A., Mitchell, R., Hartig, T., de Vries, S., et al. (2012). "Green cities and health: a question of scale?" Journal of Epidemiology and Community Health, 66(2), 160-165. https://doi.org/10.1136/jech.2011.137240 ; Sudimac, S., Sale, V., and Kühn, S. (2022). "How nature nurtures: amygdala activity decreases as the result of a one-hour walk in nature." Molecular Psychiatry, 27(11), 4446-4452. https://doi.org/10.1038/s41380-022-01720-6
  2. 9.Li, Q., Kobayashi, M., Wakayama, Y., Inagaki, H., et al. (2009). "Effect of phytoncide from trees on human natural killer cell function." International Journal of Immunopathology and Pharmacology, 22(4), 951-959. https://doi.org/10.1177/039463200902200410 (12 men, three nights, hinoki cypress oil.) ; Li, Q. (2022). "Effects of forest environment (Shinrin-yoku/Forest bathing) on health promotion and disease prevention: the establishment of 'Forest Medicine'." Environmental Health and Preventive Medicine, 27, 43. https://doi.org/10.1265/ehpm.22-00160 (board memberships declared) ; Andrade, A.M., Durães, S.D.F., Franco Netto, L.C.R., Fenner, A.L.D., et al. (2026). "Short-term cardiovascular and mental health responses to Shinrin-Yoku (forest bathing): a systematic review and meta-analysis." Frontiers in Psychology, 17, 1707829. https://doi.org/10.3389/fpsyg.2026.1707829 (Published 2026.) ; Ideno, Y., Hayashi, K., Abe, Y., Ueda, K., et al. (2017). "Blood pressure-lowering effect of Shinrin-yoku (forest bathing): a systematic review and meta-analysis." BMC Complementary and Alternative Medicine, 17(1), 409. https://doi.org/10.1186/s12906-017-1912-z ; Markevych, I., Schoierer, J., Hartig, T., Chudnovsky, A., et al. (2017). "Exploring pathways linking greenspace to health: theoretical and methodological guidance." Environmental Research, 158, 301-317. https://doi.org/10.1016/j.envres.2017.06.028
  3. 15.Chevalier, G., Sinatra, S.T., Oschman, J.L., Sokal, K., and Sokal, P. (2012). "Earthing: health implications of reconnecting the human body to the earth's surface electrons." Journal of Environmental and Public Health, 2012, 291541. https://doi.org/10.1155/2012/291541 ; Oschman, J.L., Chevalier, G., and Brown, R. (2015). "The effects of grounding (earthing) on inflammation, the immune response, wound healing, and prevention and treatment of chronic inflammatory and autoimmune diseases." Journal of Inflammation Research, 8, 83-96. https://doi.org/10.2147/JIR.S69656 ; Brown, D., Chevalier, G., and Hill, M. (2010). "Pilot study on the effect of grounding on delayed-onset muscle soreness." Journal of Alternative and Complementary Medicine, 16(3), 265-273. https://doi.org/10.1089/acm.2009.0399 ; Chevalier, G., Patel, S., Weiss, L., Chopra, D., et al. (2019). "The effects of grounding (earthing) on bodyworkers' pain and overall quality of life: a randomized controlled trial." Explore, 15(3), 181-190. https://doi.org/10.1016/j.explore.2018.10.001
  4. 16.US Food and Drug Administration. OTC Hearing Aids: What You Should Know. https://www.fda.gov/medical-devices/hearing-aids/otc-hearing-aids-what-you-should-know (Updated 3 May 2023; the rule took effect on 17 October 2022, for adults 18 and older, with sales in pharmacies and shops. Other listed signs: "You have trouble hearing speech in noisy places" and "Listening makes you tired.")
  5. 18.Hugh, S.C., Wolter, N.E., Propst, E.J., Gordon, K.A., et al. (2014). "Infant sleep machines and hazardous sound pressure levels." Pediatrics, 133(4), 677-681. https://doi.org/10.1542/peds.2013-3617 (14 machines at maximum volume; all exceeded 50 dBA at 30 cm and three exceeded 85 dBA.)
  6. 19.CDC (2024). Preventing Tick Bites, last reviewed 28 August 2024. https://www.cdc.gov/ticks/prevention/index.html
  7. 17.Coventry, P.A., Brown, J.E., Pervin, J., Brabyn, S., et al. (2021). "Nature-based outdoor activities for mental and physical health: systematic review and meta-analysis." SSM - Population Health, 16, 100934. https://doi.org/10.1016/j.ssmph.2021.100934 (50 studies, 16 randomized.)

Every work this chapter cites

The chapter's 20 notes cite 43 works, listed by note number. Each is also in the full source register.

  1. 1.Donovan, G.H., Butry, D.T., Michael, Y.L., Prestemon, J.P., et al (2013). The relationship between trees and human health: evidence from the spread of the emerald ash borer. American Journal of Preventive Medicine. 10.1016/j.amepre.2012.09.066
  2. 2.Donovan, G.H., Michael, Y.L., Gatziolis, D., Prestemon, J.P., and Whitsel, E.A (2015). Is tree loss associated with cardiovascular-disease risk in the Women's Health Initiative? A natural experiment. Health & Place. 10.1016/j.healthplace.2015.08.007Donovan, G.H., Prestemon, J.P., Gatziolis, D., Michael, Y.L., et al (2022). The association between tree planting and mortality: a natural experiment and cost-benefit analysis. Environment International. 10.1016/j.envint.2022.107609
  3. 3.Ulrich, R.S., Simons, R.F., Losito, B.D., Fiorito, E., et al (1991). Stress recovery during exposure to natural and urban environments. Journal of Environmental Psychology. 10.1016/S0272-4944(05Kaplan, S (1995). The restorative benefits of nature: toward an integrative framework. Journal of Environmental Psychology. 10.1016/0272-4944(95Gaekwad, J.S., Sal Moslehian, A., Roös, P.B., and Walker, A (2022). A meta-analysis of emotional evidence for the biophilia hypothesis and implications for biophilic design. Frontiers in Psychology. 10.3389/fpsyg.2022.750245
  4. 4.Engemann, K., Pedersen, C.B., Arge, L., Tsirogiannis, C., et al (2019). Residential green space in childhood is associated with lower risk of psychiatric disorders from adolescence into adulthood. PNAS. 10.1073/pnas.1807504116Engemann, K., Pedersen, C.B., Agerbo, E., Arge, L., et al (2020). Association between childhood green space, genetic liability, and the incidence of schizophrenia. Schizophrenia Bulletin. 10.1093/schbul/sbaa058
  5. 5.Cohen-Cline, H., Turkheimer, E., and Duncan, G.E (2015). Access to green space, physical activity and mental health: a twin study. Journal of Epidemiology and Community Health. 10.1136/jech-2014-204667Alcock, I., White, M.P., Wheeler, B.W., Fleming, L.E., and Depledge, M.H (2014). Longitudinal effects on mental health of moving to greener and less green urban areas. Environmental Science & Technology. 10.1021/es403688w
  6. 6.South, E.C., Hohl, B.C., Kondo, M.C., MacDonald, J.M., and Branas, C.C (2018). Effect of greening vacant land on mental health of community-dwelling adults: a cluster randomized trial. JAMA Network Open. 10.1001/jamanetworkopen.2018.0298Branas, C.C., South, E., Kondo, M.C., Hohl, B.C., et al (2018). Citywide cluster randomized trial to restore blighted vacant land and its effects on violence, crime, and fear. PNAS. 10.1073/pnas.1718503115
  7. 7.White, M.P., Alcock, I., Grellier, J., Wheeler, B.W., et al (2019). Spending at least 120 minutes a week in nature is associated with good health and wellbeing. Scientific Reports. 10.1038/s41598-019-44097-3BC Parks Foundation. bcparksfoundation.ca
  8. 8.Hunter, M.R., Gillespie, B.W., and Chen, S.Y (2019). Urban nature experiences reduce stress in the context of daily life based on salivary biomarkers. Frontiers in Psychology. 10.3389/fpsyg.2019.00722Meredith, G.R., Rakow, D.A., Eldermire, E.R.B., Madsen, C.G., et al (2020). Minimum time dose in nature to positively impact the mental health of college-aged students, and how to measure it: a scoping review. Frontiers in Psychology. 10.3389/fpsyg.2019.02942
  9. 9.Li, Q., Kobayashi, M., Wakayama, Y., Inagaki, H., et al (2009). Effect of phytoncide from trees on human natural killer cell function. International Journal of Immunopathology and Pharmacology. 10.1177/039463200902200410Li, Q (2022). Effects of forest environment (Shinrin-yoku/Forest bathing) on health promotion and disease prevention: the establishment of 'Forest Medicine'. Environmental Health and Preventive Medicine. 10.1265/ehpm.22-00160Andrade, A.M., Durães, S.D.F., Franco Netto, L.C.R., Fenner, A.L.D., et al (2026). Short-term cardiovascular and mental health responses to Shinrin-Yoku (forest bathing): a systematic review and meta-analysis. Frontiers in Psychology. 10.3389/fpsyg.2026.1707829Ideno, Y., Hayashi, K., Abe, Y., Ueda, K., et al (2017). Blood pressure-lowering effect of Shinrin-yoku (forest bathing): a systematic review and meta-analysis. BMC Complementary and Alternative Medicine. 10.1186/s12906-017-1912-zMarkevych, I., Schoierer, J., Hartig, T., Chudnovsky, A., et al (2017). Exploring pathways linking greenspace to health: theoretical and methodological guidance. Environmental Research. 10.1016/j.envres.2017.06.028
  10. 10.Basner, M., Babisch, W., Davis, A., Brink, M., et al (2014). Auditory and non-auditory effects of noise on health. The Lancet. 10.1016/S0140-6736(13Münzel, T., Gori, T., Babisch, W., and Basner, M (2014). Cardiovascular effects of environmental noise exposure. European Heart Journal. 10.1093/eurheartj/ehu030
  11. 11.World Health Organization (2022). Compendium of WHO and other UN guidance on health and environment, 2022 update. Chapter 11: Environmental noise. cdn.who.intNational Institute on Deafness and Other Communication Disorders (2025). Noise-induced hearing loss. nidcd.nih.gov
  12. 12.National Institute on Deafness and Other Communication Disorders (2025). Noise-induced hearing loss. nidcd.nih.govNational Institute for Occupational Safety and Health (2024). Understand noise exposure. cdc.govNational Institute for Occupational Safety and Health (1998). Criteria for a Recommended Standard: Occupational Noise Exposure (Revised Criteria 1998). cdc.gov
  13. 13.World Health Organization (2021). World Report on Hearing. who.intJarach, C.M., Lugo, A., Scala, M., van den Brandt, P.A., et al (2022). Global prevalence and incidence of tinnitus: a systematic review and meta-analysis. JAMA Neurology. 10.1001/jamaneurol.2022.2189
  14. 14.Shattock, A.J., Johnson, H.C., Sim, S.Y., Carter, A., et al (2024). Contribution of vaccination to improved survival and health: modelling 50 years of the Expanded Programme on Immunization. The Lancet. 10.1016/S0140-6736(24Jones, C.M.P., Day, R.O., Koes, B.W., Latimer, J., et al (2023). Opioid analgesia for acute low back pain and neck pain (the OPAL trial): a randomised placebo-controlled trial. The Lancet. 10.1016/S0140-6736(23
  15. 15.Chevalier, G., Sinatra, S.T., Oschman, J.L., Sokal, K., and Sokal, P (2012). Earthing: health implications of reconnecting the human body to the earth's surface electrons. Journal of Environmental and Public Health. 10.1155/2012/291541Oschman, J.L., Chevalier, G., and Brown, R (2015). The effects of grounding (earthing) on inflammation, the immune response, wound healing, and prevention and treatment of chronic inflammatory and autoimmune diseases. Journal of Inflammation Research. 10.2147/JIR.S69656Brown, D., Chevalier, G., and Hill, M (2010). Pilot study on the effect of grounding on delayed-onset muscle soreness. Journal of Alternative and Complementary Medicine. 10.1089/acm.2009.0399Chevalier, G., Patel, S., Weiss, L., Chopra, D., et al (2019). The effects of grounding (earthing) on bodyworkers' pain and overall quality of life: a randomized controlled trial. Explore. 10.1016/j.explore.2018.10.001
  16. 16.US Food and Drug Administration. fda.gov
  17. 17.Coventry, P.A., Brown, J.E., Pervin, J., Brabyn, S., et al (2021). Nature-based outdoor activities for mental and physical health: systematic review and meta-analysis. SSM - Population Health. 10.1016/j.ssmph.2021.100934
  18. 18.Hugh, S.C., Wolter, N.E., Propst, E.J., Gordon, K.A., Cushing, S.L., and Papsin, B.C (2014). Infant sleep machines and hazardous sound pressure levels. Pediatrics. 10.1542/peds.2013-3617
  19. 19.CDC (2024). Preventing Tick Bites. cdc.gov
  20. 20.Thygesen, M., Engemann, K., Holst, G.J., Hansen, B., et al (2020). The association between residential green space in childhood and development of attention deficit hyperactivity disorder: a population-based cohort study. Environmental Health Perspectives. 10.1289/EHP6729Donovan, G.H., Gatziolis, D., Derrien, M., Michael, Y.L., et al (2022). Shortcomings of the normalized difference vegetation index as an exposure metric. Nature Plants. 10.1038/s41477-022-01170-6Richardson, E.A., Mitchell, R., Hartig, T., de Vries, S., et al (2012). Green cities and health: a question of scale? Journal of Epidemiology and Community Health. 10.1136/jech.2011.137240Sudimac, S., Sale, V., and Kühn, S (2022). How nature nurtures: amygdala activity decreases as the result of a one-hour walk in nature. Molecular Psychiatry. 10.1038/s41380-022-01720-6

The full source register

This page carries the chapter's apparatus. The chapter itself, and the fifteen others, are in the book.

Get the bookThe 30-day protocolAll sixteen chapters