Being in nature is good for us. It can improve our physical and psychological health. But does nature work like exercise or eating vegetables? Is there an amount of exposure that we ought to aim for to reap the benefits? And what kind of exposure does that have to be? What if, like me, you live in a big city and have only a park nearby to provide a hit of green? A study of nearly 20,000 people published today in Scientific Reports answers these questions. For the first time, researchers have established a threshold at which spending time in nature starts to be associated with good self-reported health and high self-reported well-being: 120 minutes per week.
To their surprise, the two hours could consist of several short visits to the outdoors or one long Sunday hike. And while sitting on a park bench in a lovely green area doesn’t necessarily provide as strong a boost as climbing a mountain (or even gazing at a mountain), there was a clear benefit to sitting on a park bench over not sitting on a park bench if you did it for long enough.
The study is notable both because of the large, nationally representative sample (19,806 people across England) and because it is the first to examine weekly exposure as opposed to the effects of one visit to the outdoors. The authors see it as a first step toward a public health message around nature that doctors could conceivably recommend just as they do getting 150 minutes of exercise per week or eating five servings of fruits and vegetables per day.
There are some limitations. The study is cross-sectional, which means that it compared time in nature with self-reported mental and physical health for just one week. To prove that one thing causes the other requires a study that follows people over time and doesn't rely only on self-report. But the size of the sample and the strength of the association, even when health and other factors were taken into consideration, are promising.
I spoke to lead author Mathew White, an environmental psychologist at the University of Exeter, to talk about the significance of this new study.
Will doctors prescribe time in nature?
We’re not at this stage yet where we can say, yes, 120 minutes a week. More research needs to be done. But we think this is the first study on that path. We’re increasingly talking to doctors about social prescribing. Doctors are saying: how much time should I be saying to patients? We’ve been trying to get a realistic time that you can embed within a week.
What was really interesting for us was that it doesn’t have to be a two-hour slot. It can be accumulated bits of 30 minutes if you can fit that in your week. Or if you’re really busy and you can only go at the weekend, then two one-hour slots or a two-hour slot seem to be just as effective.
How do you know it's not just that healthier people go outside more?
Yes, the main problem [with a cross-sectional study] is that it could be that’s what we’re effectively detecting. However, because we’ve got such a large sample, a big proportion of the people, nearly 4,000, have a long-term illness or disability. And yet, they were showing exactly the same 120-minute benefit as people without that. So we know that it’s not just that healthy people visit nature. And we’ve done a lot of work experimentally outside of this showing [the health benefits of] a 30-minute time in nature. This [study] is completely consistent with experimental work. What we really need is a prospective longitudinal study which follows people’s health and well-being following changes in their amount of exposure they get. That’s the next step.
What does the experimental work show 30 minutes in nature does for your health?
When we’ve put people in [natural] environments, it decreases heart rate, decreases blood pressure, decreases stress cortisol, [and] improves psychological well-being.
What is it about nature that has this effect?
One mechanism is it encourages more exercise. In terms of the passive benefits, what I think is happening is that modern urban living is placing so many cognitive demands on us. This is downtime for our brain, giving us the chance to have space to think. Greg Bratman at the University of Washington has done work on rumination and people with mild depression. He’s showing reductions in negative rumination when people are spending time in a natural environment. That kind of process applies to everybody, whether we have a clinical diagnosis or not. I think a lot has to do with giving us mind space. The more tranquil the setting the better.
Is a city park as good as the sea or the mountains?
The type of environment does matter. There’s really good evidence to suggest that the marine environment and mountains are the top hitters. But the point here is that most people are going to urban parks. When you look at the data, it’s still okay. The 120-minute threshold still applies. The park is better than walking down a busy street.
And you don’t have to be exercising?
Exercise in nature is really valuable. But here we’re controlling for that statistically, so this is the effect over and above exercise. Because we’ve got such a large sample, we looked at people who don’t do any exercise, or very little, and we looked at whether their time in nature, which is largely sitting on benches and having picnics, is good. And it was as well. We know exercise is good, we know exercise in nature is good, but this effect applies even if you spend time in nature for relaxation.
Copyright: Lydia Denworth, 2019