So-called "nature prescriptions" - when doctors recommend spending more time in nature - have been found to reduce patients' blood pressure, increase daily step counts and lower depression and anxiety scores.

Australian academics who reviewed 92 international studies in which participants were prescribed time engaging with nature found reduced levels of chronic stress and increased healthy behaviours such as socialising and physical activity.

Lead researcher Professor Xiaoqi Feng from University of NSW Medicine and Health said the evidence showed nature prescriptions helped restore and build better physical and mental health.

"Contact with nature - and trees especially - is really good for strengthening mental and physical health across our lives," Prof Feng said.

"How can we encourage and enable people to reconnect with nature?

"That's where the idea of a nature prescription comes in."

Prof Feng and co-lead researcher Prof Thomas Astell-Burt from the University of Wollongong recently secured a $1.5 million government grant through the Medical Research Future Fund to test the effectiveness of nature prescriptions in Australians aged 45 and older.

Living close to certain types of green space can also improve health.

Those living in areas with 30 per cent or more tree canopy reported better general health and reduced psychological distress, a study of almost 47000 adults in NSW also conducted by Prof Feng found.

The research has informed the City of Sydney's $377 million strategy to reach 40 per cent green cover by 2050.

"But even if you have a high-quality green space like a park nearby, it doesn't mean that everyone will visit and benefit from it," Prof Feng said.

"What we need now is to work out how to make nature prescriptions happen in a sustained way for those people with high potential to benefit, but who currently spend little time in nature."

Nature prescriptions are emerging as a supplement to standard medical care.

In the UK, a pilot program has been introduced for "green social prescribing" and Canada has a national nature prescription program.

Prof Feng is pushing for large-scale nature prescription programs in Australia.

"How long should the nature prescription be for? What should be in the prescription? How should we deliver it, and by whom?

"These questions don't have firm answers yet," she said.

"If we want nature prescriptions to become a national scheme, we really need to provide the evidence."

Prof Feng cautioned against these prescriptions being a "luxury item for the rich" who already have access to beaches and high-quality green space.

"We want these benefits for everyone," she said.