Gardening as therapy has always been a good idea. British prisoners have gardens. Sunshine and exercise are good for exercise and if you also grow what you eat that often means you eat better foods.

The dirt work is interesting too. In the UK it is certainly known that children who crawl in dirt and whose parents are not too fussy about hygiene are less likely to get asthma (the excuse I used to use for having grubby crawling toddlers anyway when mine were small).

We would always have had a lot of contact with dirt in the millions years of our history anyway so it would not be surprising if a disassociation from nature and soil and dirt might be something after all those thousands of years of being in touch with the soil which may be wrong.

Sounds like digging a vegetable patch might be the way to go.