Spending time among nature is only beneficial if it is done for more than two hours a week, a new study suggests.
Researchers found that people who spend at least 120 minutes in nature a week are significantly more likely to report good health and higher psychological wellbeing than those who do not visit nature at all during an average week.
No such benefits were found for people who visited natural settings such as town parks, woodlands, country parks and beaches for less than two hours a week.
Experts say taking a walk in the woods, listening to birdsong, looking around and engaging with nature lowers stress and blood pressure.
Last year, NHS Shetland became the first organisation to start prescribing nature walks to patients.
The University of Exeter-led study used data from nearly 20,000 people in England and found that it did not matter whether the 120 minutes was achieved in a single visit or over several shorter visits.
It also found the 120-minute threshold applied to both men and women, to older and younger adults, across different occupational and ethnic groups, among those living in both rich and poor areas, and even among people with long term illnesses or disabilities.
Study leader Dr Mat White said: "It's well known that getting outdoors in nature can be good for people's health and wellbeing, but until now we've not been able to say how much is enough.
"The majority of nature visits in this research took place within just two miles of home so even visiting local urban greenspaces seems to be a good thing.
"Two hours a week is hopefully a realistic target for many people, especially given that it can be spread over an entire week to get the benefit."
There is growing evidence that merely living in a greener neighbourhood can be good for health, for instance by reducing air pollution.
The data for the current research came from Natural England's Monitor of Engagement with the Natural Environment Survey, the world's largest study collecting data on people's weekly contact with the natural world.
Co-author Professor Terry Hartig, of Uppsala University in Sweden, added: "There are many reasons why spending time in nature may be good for health and wellbeing, including getting perspective on life circumstances, reducing stress, and enjoying quality time with friends and family.”