There are a lot of studies that show even just sitting under a tree every day, lowers our stress, which can then, in turn, lower blood pressure, heart rate and those stress hormones, like cortisol. There's a natural calming effect created by breathing in fresh air and focusing on the sounds and sights around you. It's even proven to help people suffering from anxiety and depression. There's studies that are ongoing about how that could potentially help people who have ADHD. It's been shown it can improve our memory even so it could be even more cognitively active when we come back from being outside.
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