This study adds to growing evidence that combining activities such as walking or cycling with nature boosts well-being.

From an analysis of 1,252 people (of different ages, genders and mental health status) drawn from ten existing studies in the United Kingdom, the authors were able to show that activity in the presence of nature led to mental and physical health improvements.

The greatest health changes occurred in the young and the mentally-ill, although people of all ages and social groups benefited. All natural environments were beneficial including parks in urban settings.

The research looked at many different outdoor activities including walking, gardening, cycling, fishing, boating, horse-riding and farming in locations such as a park, garden or nature trail.

The biggest effect was seen within just five minutes.

With longer periods of time exercising in a green environment, the positive effects were clearly apparent but were of a smaller magnitude, the study found.

"For the first time in the scientific literature, we have been able to show dose-response relationships for the positive effects of nature on human mental health," the author said.

A bigger effect was seen with exercise in an area that also contained water - such as a lake or river.

The study leader said those who were generally inactive, or stressed, or with mental illness would probably benefit the most from "green exercise".

"We know from the literature that short-term mental health improvements are protective of long-term health benefits,"

"So we believe that there would be a large potential benefit to individuals, society and to the costs of the health service if all groups of people were to self-medicate more with green exercise," the author said.

Research Paper Details:

Jo Barton, Jules Pretty. What is the Best Dose of Nature and Green exercise for Improving mental health? A Multi-Study Analysis. Environmental Science & Technology, 2010.