Where you walk, not whether you walk

Most research on this compares people who spend time outdoors with people who do not, which tells you almost nothing, because those are different people leading different lives. The review this page rests on did the harder thing. Across twenty-four experimental studies, the same physical activity - almost always a walk, sometimes a jog or a run - was carried out in a green natural setting and in an urban one. In eighteen of the twenty-four, the same people did both routes; the remaining six compared two separate groups. Commercial districts, historical downtowns, city centres and residential streets on one side; forests, woodland, grassland, nature reserves and urban parks on the other. Both arms were outdoors. Both arms were moving. The only thing that changed was the scenery. Results favoured the natural setting for anxiety, anger and hostility, energy, general affect and positive engagement.

Wicks C, Barton J, Orbell S, Andrews L 2022

Six outcomes could be combined statistically, and all six favoured the natural setting. The steadiest of them was vigour - how energetic people felt afterwards - where five studies of 697 people agreed closely with one another. Those five are not a separate piece of research: the twenty-four-study statement above is the review's written summary of everything it found, while each combined figure rests on its own smaller subset of those same studies. They are two views of one review, not two independent confirmations of each other. But these are differences in scores on a mood questionnaire whose scale the review never names, so a number like 3.28 cannot honestly be translated into anything you can picture. There is one number this page deliberately will not print: the combined figure for anxiety. The studies behind it disagreed with each other so violently that the pooled result came out at a size no realistic effect reaches, and quoting it would tell you something false about how big this is. The direction is worth acting on. The magnitude is not established.

Wicks C, Barton J, Orbell S, Andrews L 2022

Nearly every one of these studies was a single walk with a questionnaire filled in immediately afterwards, in healthy adults with no physical or mental health conditions - and two thirds of the samples were university students. So this is evidence about how you feel at the end of a walk, not about depression, not about anxiety disorders, not about anything a month later, and not about your physical health. Even within mood, the direction was not uniform: results for depression, tranquillity and calmness were mixed. And nobody in any of these studies could be blinded, for the obvious reason that you can see where you are walking, which is part of why the reviewers rated the risk of bias as high.

Wicks C, Barton J, Orbell S, Andrews L 2022

There is a much larger body of work showing that people who live in greener areas are healthier: in a systematic review and meta-analysis of greenspace and physical health, greener areas were linked to lower odds of type II diabetes, of all-cause mortality and of several birth outcomes. It is tempting to hand that to you as the reason to walk through a park. It is not a reason, because it compares places and the people in them. Greener areas also have more money, cleaner air, less noise and more room to move, and nothing in that design separates the greenery from the rest of it. Two more things worth knowing: several of those pooled comparisons found nothing at all - high blood pressure, stroke, systolic blood pressure, dyslipidaemia, asthma - and that review deliberately excluded mental health outcomes altogether, so it is not evidence for anything on the rest of this page.

Twohig-Bennett C, Jones A 2018

Linked to it, and this page will not say more than that. The design is stronger than most - the setting was assigned, and in most of these studies the same person did both routes - but only some of them randomised properly, none reported whether one walk carried over into the next, and the reviewers rated the overall risk of bias as high. What can be said plainly is that when researchers held the activity constant and changed only the surroundings, the surroundings still made a measurable difference to how people felt. That is a real finding and it is not the same as proof.

Lower and shorter than you would expect. The natural settings in these studies were not all wilderness - they included urban parks, grassland, woodland and a regenerated landfill site, and the urban comparisons were ordinary commercial districts and residential streets. The sessions ran from fifteen minutes to an hour. What has not been established is a dose: the review could not analyse duration properly, so there is no threshold to give you, and anyone quoting a specific number of minutes in nature is going beyond this evidence.

Then this particular lever is not available to you, and it is more honest to say so than to invent a substitute. Nothing in this evidence tests looking at a picture of a forest, a plant on a desk or a window view, so this page makes no claim about those. What it does not change is that the walk itself is still worth taking - the comparison here was always green route against grey route, never walking against not walking. If the greenest thing on your route is a line of street trees or a single square, that is the version of this you have, and it is closer to what was studied than nothing is.