Nature

Green space and mental health: what the numbers say

Living near green space goes with measurably better mental health, and the pattern shows up in very different study designs: in a Danish register study of 943,027 people, those who grew up with the least vegetation around their home had up to 55% higher risk of a psychiatric disorder later in life than those with the most. Among 46,786 Australian adults, having 30% or more tree canopy within 1.6 km of home, compared with under 10%, went with 31% lower odds of developing psychological distress over an average of 6.2 years, and in a randomised trial in Philadelphia, turning empty lots into small green spaces cut residents' reports of feeling depressed by 41.5%. A WHO review of urban green space notes that a 5-minute walk, or up to 300 metres from home, is often defined as an acceptable distance.

What the studies actually measure

Green space in research is rarely a park you would recognise by name. Most large studies take satellite images and calculate a vegetation index (NDVI) around each home, so a tree-lined street, a back garden and a football pitch all count, and the quality of the space does not. The Danish study used 30-metre satellite pixels within a 210 by 210 metre square around each address, the smallest of 4 square sizes tested, for every year from birth to age 10. The Australian study split total green cover into tree canopy, grass and other low vegetation within a 1.6 km road network buffer around the home. Mental health is measured differently too: diagnoses from a national psychiatric register, a distress questionnaire, or a single survey question about feeling depressed.

Keep 2 things in mind while reading the numbers. Almost all of the evidence is observational, so it shows association rather than proof of cause. Greener neighbourhoods tend to be wealthier, quieter and less polluted, and people who are already well may be the ones who move to them. The better studies adjust for income, education and urbanisation, and 1 is a randomised trial, but none can rule out every alternative explanation. The effects are also population averages: 31% lower odds of distress in a cohort of 46,786 people says nothing about what a Sunday in the park will do for you.

Childhood green space and later psychiatric risk

The largest study of this question comes from Aarhus University and was published in PNAS in 2019. It linked 943,027 people born in Denmark between 1985 and 2003 to the national psychiatric register and to satellite data on the vegetation around every address they lived at from birth to their 10th birthday. People who grew up with the lowest level of green space had a higher rate of later psychiatric disorder than those with the highest, for every diagnosis studied except intellectual disability and schizoaffective disorder. The excess ranged from 15% to 55% depending on the disorder. The association was strongest in the centre of the capital region (incidence rate ratio 1.60, 95% confidence interval 1.42 to 1.80) and weakest in rural areas (1.27, 1.22 to 1.33).

Two details make the finding harder to explain away. The association changed little after adjusting for urbanisation, parents' socioeconomic status, family history of mental illness, parental age and municipal factors. And cumulative green space across all 10 childhood years was more strongly associated with risk than green space in any single year, which is what you would expect if the exposure itself matters. The authors still note that they cannot fully exclude genetic confounding: parents' own traits may shape both where a family lives and a child's later risk.

Trees, grass and adult distress

Does the type of green matter? Researchers at the University of Wollongong followed 46,786 adults in the 45 and Up Study in New South Wales for an average of 6.2 years (JAMA Network Open, 2019). Psychological distress was measured with a standard 10-item questionnaire and general health with a single self-rated question. Compared with people who had 0 to 9% tree canopy within 1.6 km of home, those with 30% or more had odds of 0.69 (95% CI 0.54 to 0.88) of developing psychological distress during follow-up and odds of 0.67 (0.57 to 0.80) of moving into fair or poor general health. In plain terms, about 31% lower odds of new distress and 33% lower odds of declining health. One outcome moved with nothing: no green space measure was linked to physician-diagnosed depression or anxiety, at the start or during follow-up, and for 30% or more canopy the odds were 0.86 (0.74 to just above 1.00). The benefit in this cohort sits in a distress questionnaire and in self-rated health, not in diagnoses.

Grass told a different story. People with 30% or more grass cover, compared with 0 to 4%, had higher odds of distress already present at baseline (1.71, 1.25 to 2.28) and of newly reporting fair to poor health by follow-up (1.47, 1.12 to 1.91). Open grassland in Australian suburbs often means sports fields, verges and undeveloped land at the urban fringe rather than shaded, usable space, so the lesson is not that lawns harm you but that a percentage of green on a map is a crude measure, and that mature trees seem to carry most of the benefit. The health outcomes were self-reported and the green cover was mapped in 2016, years after the baseline survey, so the study cannot show that the trees came first.

A trial in Philadelphia and a British panel study

Observational studies cannot randomise where people live, but one trial came close. In Philadelphia, researchers from the University of Pennsylvania randomly assigned 541 vacant lots, grouped in 110 clusters, to 3 arms: greening (the lot cleared, planted with grass and a few trees, and edged with a low wooden fence), rubbish removal only, or no intervention. They surveyed 442 residents living nearby in 2 waves before the work, which was carried out in April and May 2013, and in 2 further waves over the 18 months after it; 342 had follow-up data and were analysed. Compared with the untouched lots, people near greened lots reported feeling depressed 41.5% less often (between 5.9% and 63.6% less) and feeling worthless 50.9% less often. In neighbourhoods below the poverty line, reports of feeling depressed fell by 68.7%. Rubbish removal on its own changed nothing measurable.

The trial is small, measures single items from a standard 6-question distress scale rather than clinical diagnoses, and did not track whether residents used the lots, so the mechanism stays open: less visible neglect, more neighbours outside, or simply a view of something growing. A British panel study adds the time dimension. Using the British Household Panel Survey, Alcock and colleagues at the University of Exeter followed 1,064 people who moved home, with General Health Questionnaire scores for 5 consecutive years around the move. The 594 who moved to greener urban areas had significantly better scores in each of the 3 years after moving (P = 0.015, 0.016 and 0.008), with no sign of the effect fading. The 470 who moved to less green areas scored worse in the year before the move, which the authors read as anticipation, and then returned to their old baseline.

How close, how much, and what you can do

How near does green need to be? The WHO Regional Office for Europe reviewed urban green space interventions in 2017, screening 6,997 studies and including 38, alongside 48 case studies from 14 countries. Its good practice guidance is that green space should be physically accessible within a short distance of local homes, with a footnote adding that a 5-minute walk, or up to 300 metres, is often defined as an acceptable distance. The review also found that physical improvements to a space worked best when paired with a programme that promoted its use, which fits the Philadelphia result: the change has to be visible and usable, not just present on a map.

For time rather than distance, the best-known figure is 120 minutes a week in natural settings, covered in our guide on 120 minutes in nature a week; how you split those minutes did not seem to matter. The Nature Dose Planner turns that into a weekly plan. If your street has no trees, a park 300 metres away still counts, and so does a route to work that passes through one. Gardening, an allotment or a balcony of plants add exposure you control yourself; see gardening as exercise and therapy.

Two cautions. None of these studies tested green space as a treatment, and none replaced medication or therapy with a walk. The NHS advises seeing a GP if symptoms of depression last most of the day, every day, for more than 2 weeks, and that advice does not change because a park is nearby. If you have a heart condition, take diabetes medication or are pregnant, a new outdoor routine is still a change in activity, so mention it at your next appointment. The green in this guide is a background condition of daily life, cheap and largely free of side effects, which is exactly why planners and health services are paying attention.

Ways to add green to an ordinary week

Frequently asked

Does a small city park count as green space?

Yes. The WHO review notes that a 5-minute walk, or up to 300 metres, is often defined as an acceptable distance to green space, and in the Philadelphia trial the greened sites were single vacant lots, not parks. Being close enough to see and use daily matters more than size.

Is it the trees or the exercise that helps?

Probably both, along with quieter surroundings, cleaner air and more contact with neighbours. The Australian cohort found the benefit in tree canopy but not in grass, and the Philadelphia trial found an effect without tracking whether anyone used the lots, so simply living beside greenery seems to contribute.

I grew up in a city with little green. Is the childhood finding bad news for me?

The Danish study describes population risk, not individual fate. Even in the least green decile most people never developed a psychiatric disorder, and the 15 to 55% figures are relative increases on modest baseline risks. Green space in adult life still showed benefits in the Australian and British data.

Can time in green space replace treatment for depression or anxiety?

No. None of the studies tested green space as a treatment, and the effects are averages across whole populations. If low mood or anxiety has lasted more than 2 weeks, see your GP; green space can sit alongside therapy or medication, not in place of them.

How much time in green space do I need?

The most cited figure is 120 minutes a week in natural settings, and it did not seem to matter whether that came in 1 long visit or several short ones. The Nature Dose Planner on this site helps you plan it around the parks and paths you actually have.

Sources

• Engemann et al. 2019, PNAS: Residential green space in childhood is associated with lower risk of psychiatric disorders from adolescence into adulthood · 943,027 people born in Denmark 1985 to 2003; full text on PubMed Central
• South et al. 2018, JAMA Network Open: Effect of greening vacant land on mental health of community-dwelling adults, a cluster randomized trial · 541 lots, 342 residents analysed, Philadelphia; the journal site answers 403 to automated requests, content verified in a browser-like fetch
• Astell-Burt and Feng 2019, JAMA Network Open: Association of urban green space with mental health and general health among adults in Australia · 46,786 adults in the 45 and Up Study; the journal site answers 403 to automated requests, content verified in a browser-like fetch
• Alcock et al. 2014, Environmental Science and Technology: Longitudinal effects on mental health of moving to greener and less green urban areas · 1,064 movers in the British Household Panel Survey; the journal site answers 403 to automated requests, abstract verified via Europe PMC
• WHO Regional Office for Europe 2017: Urban green space interventions and health, a review of impacts and effectiveness · 38 intervention studies from 6,997 screened and 48 case studies; a 5-minute walk or up to 300 m often defined as an acceptable distance

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This guide is for general information. It does not replace medical advice or an examination.