It’s a medical fact: Spending time outdoors, especially in green spaces, is good for you.

A wealth of research indicates that escaping to a neighborhood park, hiking through the woods, or spending a weekend by the lake can lower a person’s stress levels, decrease blood pressure and reduce the risk asthma, allergies, diabetes and cardiovascular disease, while boosting mental health and increasing life expectancy. Doctors around the world have begun prescribing time in nature as a way of improving their patients’ health.

One question has remained: How long, or how frequently, should you experience the great outdoors in order to reap its great benefits? Is there a recommended dose? Just how much nature is enough?

According to a paper published Thursday in the journal Scientific Reports, the answer is about 120 minutes each week.

The study examined data from nearly 20,000 people in England who took part in the Monitor of Engagement with the Natural Environment Survey from 2014 to 2016, which asked them to record their activities within the past week. It found that people who spent two hours a week or more outdoors reported being in better health and having a greater sense of well-being than people who didn’t get out at all.