There is a mountain of research on how time in nature impacts people’s physical and mental health, from lowering stress and blood pressure to increasing life expectancy. Which is why more doctors are now actually prescribing nature. But what’s the right dose? A new UK study (20,000 people) provides an answer: two hours a week. People who spent 120 minutes outdoors each week reported being in significantly better health and had a greater sense of wellbeing than those that didn’t get out. An hour or an hour and a half didn’t have as big an effect and five hours didn’t seem to add health benefits. The positive impact was true for old and young, men and women, and rich and poor.