From the North Shore to the southern plains, Minnesotans have no shortage of places to take in nature. Researchers have found that having short experiences with nature — even 20 minutes — can reduce cortisol levels. (Star Tribune file/The Minnesota Star Tribune)

If you're feeling stressed, there's handy remedy: a "nature pill."

Granted, it isn't actually a pill. It works faster than a pill and, as prescriptions go, is much easier to refill.

All you need to do is go outside.

Researchers from the University of Michigan conducted a study to determine the association between nature and stress hormone levels.

For the assessment, they asked a group of adults to take "nature pills" — to spend some time sitting or walking in nature. They were required to spend 10 minutes or more in nature at least three times a week for an eight-month period.

Once every two weeks, the scientists measured the participants' levels of cortisol, a stress hormone, using saliva samples taken before and after a nature pill.

"Participants were free to choose the time of day, duration and the place of their nature experience, which was defined as anywhere outside that, in the opinion of the participant, made them feel like they've interacted with nature," said MaryCarol Hunter, lead author of the study, which was published in Frontiers in Psychology.

"There were a few constraints to minimize factors known to influence stress: take the nature pill in daylight, no aerobic exercise, and avoid the use of social media, internet, phone calls, conversations and reading," she said.

In addition to accommodating the subjects' busy lifestyles, the team also factored in the natural drop in cortisol levels that can occur naturally throughout the day.

After analyzing the results, they found that having a 20-minute nature experience reduced cortisol levels. Those who spent 30 minutes sitting or walking outside had the greatest decrease of cortisol levels.

"Our study shows that for the greatest payoff, in terms of efficiently lowering levels of the stress hormone cortisol, you should spend 20 to 30 minutes sitting or walking in a place that provides you with a sense of nature," Hunter said.

The team said that the findings provide the first estimates of how nature can affect our daily lives, and that it hopes that health care providers take advantage of the evidence.

"Our experimental approach can be used as a tool to assess how age, gender, seasonality, physical ability and culture influence the effectiveness of nature experiences on well-being," Hunter said. "This will allow customized nature pill prescriptions, as well as a deeper insight on how to design cities and well-being programs for the public."