It's no secret that spending time in nature can be good for your health. Now, researchers, who published their results in the journal Nature Scientific Reports, say they’ve found the minimum dose of nature time required to reap the benefits: 30 minutes a week.

Earlier studies concluded that spending time in green and blue spaces like the park and the beach may lower blood pressure, reduce stress and anxiety, and even keep us alive longer. But “nature” can be kind of a slippery concept. There’s no scientific consensus on what “nature” is, which means that each experiment has relied on its own definition. And while those studies agreed that nature time is good medicine, few have tried to identify the right dose.

To address the latter, a team of researchers surveyed 1538 residents of the city of Brisbane, Australia. The participants were between the ages of 18 and 70 years old and were evenly mixed in age, gender, income, and socioeconomic status. The survey was pretty holistic, asking participants about not only their physical and mental health but also their work hours, family situations, exercise habits, and, of course, time spent outdoors. And rather than defining terms, the researchers simply asked participants to answer based on what they considered "outdoor green space."

The survey results certainly supported earlier research; even after controlling for factors like exercise and socioeconomic status, nature time was associated with better health. But a monthly five-minute stroll across the city green wasn’t enough. To really see nature’s salutary effects, participants had to log at least 30 minutes per week. Thirty minutes of park time per week really isn’t that much, if you think about it, but it does require effort, interest, and resources. Forty percent of respondents said they hadn’t visited a park in the last week at all, let alone for a half-hour.

Lead author and University of Queensland biologist Danielle Shanahan sees this as great news. "If everyone visited their local parks for half an hour each week, there would be 7 percent fewer cases of depression and 9 percent fewer cases of high blood pressure," she said in a press statement.

"Given that the societal costs of depression alone in Australia are estimated at $A12.6 billion a year, savings to public health budgets across all health outcomes could be immense," she said.

The results do come with one big caveat. Survey responses showed a correlation between nature time and better health, but they didn't show causation. It’s possible, for example, that people with depression and high blood pressure have a harder time getting to the park; depression can make it very hard to leave the house, and high blood pressure could be worsened by a nonstop schedule. Just the same, these results are encouraging, and surely a little time in a soothing green space is a good thing.

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