Is too much exposure to outdoors bad?

MELBOURNE: Several studies have linked exposure to nature with improved human health and well-being. But how much of the nature's dose do we really need?

Researchers are trying to find a precise "nature dose" that can trigger positive effects on health.

"Urban green spaces provide settings for a remarkable range of physical and mental health benefits, and pioneering health policy is recognising nature as a cost-effective tool for planning healthy cities," said study leader Danielle F. Shanahan from the Fuller Lab, Australia.

The findings are of growing importance given that in the near future, 70 percent of the world's population will live in cities, where they will face a rising tide of lifestyle-related disease.

Despite this, limited information is available on how specific elements of nature deliver health outcomes.

There is an absence of clear evidence about which elements of nature deliver which health outcomes.

For example, three separate studies led by ecologists reported different effects of the number of bird and plant species in an area on self-reported well-being.

"They variously found a positive effect, an effect that was dependent on perceived species richness, and no effect," the researchers noted.

The authors hope "to understand how urban nature can be manipulated to enhance human health" through "dose-response" modelling.

Nature exposure can occur in a variety of ways, from rural forest excursions to greenery viewed from an office window, and the differential effects of exposures require careful study.

The authors describe several possible dose-response curves and find that plateaus in health responses are to be expected.

Surprisingly, increased crowding and complexity of greenery in cities could even "decrease a person's feeling of safety and increase stress", according to the researchers.

"We need cost-effective and tailored solutions that could enhance population health and reduce health inequalities," Shanahan said.

The study is scheduled to be published in BioScience.

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