Most nature trials compared nature with doing nothing

The largest review doubts its own figure

All four reviews on nature reported less anxiety, depression or stress, or positive associations with health. The psychologist Esmaeel Saeedy Robat and colleagues wrote the largest of them. They collected 116 systematic reviews, pooled the results of 30 of them and published the analysis in Nature Human Behaviour in 2026. Their base is 3,870 primary studies with an estimated 10 million people.

Programmes in nature lowered anxiety by 0.83 standard deviations and depression by 0.72. A standard deviation is the usual spread of scores around the average. By the common convention, a gap of 0.8 or more counts as large, which puts the anxiety figure in that range.

Saeedy Robat and colleagues also explain why these figures run high. Most of the underlying trials compared people in a nature programme with people who did nothing at all, and such a trial cannot separate the effect of the activity from the effect of nature. The authors call the pooled figure almost certainly larger than the real effect. They leave its true size open until more trials give the control group an activity too.

Outdoor exercise did better than indoor exercise

The one review with an active comparison came from the anaesthesiology researcher Yun Liang and colleagues. In Frontiers in Public Health in 2026, they combined 15 randomised trials with 809 adults in a network meta-analysis, a model that ranks several treatments at once, including pairs that no single trial compared. They set exercise in green space against the same exercise indoors and against no exercise.

On a combined measure of depression, anxiety and distress, green exercise scored 0.96 standard deviations better than no exercise and 0.75 better than indoor exercise. Indoor exercise had a small effect against no exercise, one that chance alone could explain. The model ranked green exercise first of the three with near certainty. Liang and colleagues read the outdoor setting as producing part of the gain and present the result as a direction for further trials to test.

Recorded sound eased anxiety more than video

A copy of nature also lowered stress and anxiety in 36 randomised trials with 2,925 people. The psychologist Yuhan Zhou and colleagues pooled these trials on portable digital nature, meaning nature on a screen, in a sound recording or through a headset, and published the meta-analysis in Clinical Psychology Review in 2026. Stress fell by a Hedges' g of 0.51, anxiety by 0.67 and depression by 0.26. Hedges' g uses the same scale of standard deviations, corrected for small samples.

For anxiety, sound alone worked better than video. It also worked better than full multisensory setups, which address sight, hearing and further senses at once.

The European evidence is thin on equity

The environmental economist Diya Chakravorty and colleagues reviewed 115 European studies on nature-based solutions and health and published the review in Environments in 2026. Nature-based solutions use parks, forests, rivers and other natural areas to improve living conditions. Almost 88% of the quantitative studies reported at least one positive association with health. Mental health came up nearly twice as often as physical health.

The studies come mainly from the United Kingdom and Spain, and Chakravorty and colleagues name short interventions of low intensity as a gap. Almost none examined whether a new park reaches the residents most at risk or the people who already live near green space.

The real effect is smaller than the pooled one

I think contact with nature lowers anxiety and depression, but only trials with an active comparison can show by how much. Among the seven reviews, Liang and colleagues alone made such a comparison, with 15 trials and 809 adults. I read the large pooled effects as an upper bound and expect the real effects to be smaller than 0.83 and 0.72.

With a limited budget, I would favour moving exercise outdoors over the same exercise indoors. For anxiety, I would test a sound recording before buying an immersive room.

Sources

• Saeedy Robat and colleagues 2026, "A systematic overview and second-order meta-analysis of nature-based interventions for stress, anxiety and depression", Nature Human Behaviour 10(8):1495-1509. https://doi.org/10.1038/s41562-026-02433-4
• Liang, Wei and Min 2026, "Comparative efficacy of green exercise versus indoor exercise for depression and anxiety: a systematic review and network meta-analysis", Frontiers in Public Health 14:1831073. https://doi.org/10.3389/fpubh.2026.1831073
• Zhou and colleagues 2026, "Effectiveness of portable digital nature experience on mental health: A three-level meta-analysis of randomized controlled trials", Clinical Psychology Review 127:102748. https://doi.org/10.1016/j.cpr.2026.102748
• Chakravorty and colleagues 2026, "Nature-Based Solutions and Human Health in Europe—A Systematic Review", Environments 13(6):300. https://doi.org/10.3390/environments13060300
• The Built Review, "How much of nature's benefit is really the nature?", trend report Q3 2026, July 2026. https://thebuiltreview.com/trend/q3-2026