When I get stressed, my husband tells me to go and see "Dr. Koolio".
There is no question that the horses improve my physical and mental well-being. Maybe it is because horses are my passion, and maybe it is something else. I find my horses, especially Koolio, acts as a mirror of my soul. When I am anxious, he is anxious. As I relax, he relaxes. He is the ultimate bio-feedback mechanism both in the saddle and on the ground. If I want him to find a sense of balance, rhythm and relaxation under saddle, I must first do the same. If I want him to let go of his fears on the trail, I have to let go of those I have quietly waiting in the back of my own mind.
I am fortunate to be able to keep my horses in my back yard, where I can access a little bit of "magic horse breath" any time I need or want to. The daily requirements of feeding the horses, checking the fence, water, etc, and just managing our property ensures that I get some physical exercise every single day. This daily routine also keeps me much healthier than I was before I had my horses at home.
So, yes, horses do dramatically improve both your physical and mental well-being.