Your local city park may be improving your health, according to a new paper led by Stanford University researchers. The research, published in Proceedings of the National Academy of Sciences, lays out how access to nature increases people’s physical activity—and therefore overall health—in cities. Lack of physical activity in the U.S. results in $117 billion a year in related health care costs and leads to 3.2 million deaths globally every year. It may seem like an intuitive connection, but the new research closes an important gap in understanding how building nature into cities can support overall human wellbeing.