Recent studies have shown that children today are spending less than half of their time outdoors when compared to their parents. Furthermore, data shows that the average screentime per day is over 10-hours per day and that it's only going up. Finally, due to the increase of time indoors the EPA has started to study the effects of indoor air quality and how it impacts the health of people.
Numerous studies have occurred over the past several years regarding the benefits of being in nature. One particular study showing the difference in a 45-minute forest walk when compared to a 45-minute walk in an indoor laboratory resulted in:
12% decrease in the presence of the stress hormone cortisol
7% decrease in sympathetic nervous system activity (the fight-or-flight system)
1.4% decrease in blood pressure
6% decrease in heart rate
Additional benefits included improved sleep and vigor, along with the activation of the parasympathetic nervous system which has a positive benefit on immunity.
Research continues to happen in this space, however, simply looking at that for 99% of the time humans have been on planet earth we have lived in amongst the more-than-human world vs. living indoors, it's only natural that our bodies are adapted to spending time in nature.