Nature itself is the best physician
https://sitn.hms.harvard.edu/flash/2...est-physician/
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Not only does spending time in nature improve our mental wellbeing, but it also improves our physical well-being, such as immune health and blood pressure. Time spent in nature has been associated with increased expression of anti-cancer proteins and natural killer (NK) cells– immune cells that can kill tumor cells or cells infected with viruses.
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One hypothesis attributes the observed effects on immune function to breathing in phytoncides, volatile organic compounds that have antifungal and antibacterial properties that are released into the air by trees. Lab studies have indicated that phytoncides increase natural killer (NK) cell activity. Therefore, it is plausible that exposure to phytoncides in forests explains the enhanced NK cell function in people who spent time in forests. ..."