Stop and smell the roses along the way, American singer-songwriter Mac Davis advised in a top 10 hit in the 1970s. In the more than three decades Davis imparted that wisdom, numerous studies have confirmed the link between exposure to nature and improved physical, psychological and social well-being. They have shown that greenery has been associated with reduced levels of asthma, improved healing times and even with making people more likely to exercise.

Over the past few years, a booming ecosystem of therapists, bootcamp coaches and others have embraced the concept of "ecotherapy," but there has been little research so far about how much we actually need to stay healthy.

The White House on Tuesday recognized the links between people's well being and their environment by launching an initiative focusing on the connections between climate change and public health. The administration is bringing health and data experts in to discuss strategies on how to address this issue. And President Obama has put a personal face on the initiative by talking about his daughter Malia's asthma.

The question of how to help man better adapt to changes in our habitats -- both due to global climate changes and migration --  is increasingly important as more and more people move to cities where pollutants can be higher and opportunities to commune with nature may be fleeting. The World Health Organization predicts that 70 percent of the world's population will live in urban areas within 30 years.

To address this demographic trend, a team of scientists has begun to study how to define a "nature dose" in an effort to develop recommendations for minimum levels of exposure in the same way doctors do for things like Vitamin D, vegetables or medicines. At a macro level, that information could be used by public health experts, ecologists, sociologists, and urban planners to help figure out how to plan and manage cities in a way that could boost health outcomes.

"A major consequence of continued urbanization is that more people will be exposed to the health risks associated with city living. Urban nature could provide a cost-effective tool to reduce these health risks," Danielle F. Shanahan from the University of Queensland in Australia and her colleagues wrote in the journal Bioscience on Wednesday.

Their goal, the researchers wrote, is "to understand how urban nature can be manipulated to enhance human health" and propose a framework for "measuring" nature doses such as the intensity (i.e. the number of street trees in a neighborhood or percentage of vegetation cover in a landscape), frequency or pattern and duration of exposure. They noted that there are some challenges in defining a dose "largely because it can be framed in a social context as well as an objective reality."