Last week, we posted a piece on 5 small dog breeds that make great senior life companions in honor of National Dog Day in the dog days of summer. And we briefly mentioned that dog ownership can have great emotional benefits. The simple act of caring for a pet can be a way to reduce feelings of loneliness and develop the positive feelings associated with companionship.

But the benefits of pet ownership are not just emotional. Increasing evidence supports the supposition that having a pet may yield physical health benefits, too.  Here are some of the findings.

Therapy pets

If you have been to a hospital in the last 10 to 15 years, you are likely at some point to have seen someone walking a dog in the hallways. There hasn't been a relaxing of the rules— naturally, you can't bring your own pet to the hospital. But there are a growing number of trained, licensed therapy dogs who visit patients with hospital volunteers.

Therapy dogs may first have been used during World War II. Some accounts state that a small Yorkshire terrier named Smoky, who belonged to Corporal William A. Wynne (an aerial recon photographer), was allowed to visit battlefield casualties at the 233rd Station Hospital on New Guinea. The commanding officer of the surgical hospital, Dr. Charles William Mayo (of the Mayo Clinic) noticed that soldiers who interacted with Smoky showed marked improvement in their level of stress and anxiety, and this seemed to improve medical outcomes.

After the war, Smoky returned to the United States with her owner and continued serving as a volunteer therapy dog until her death in 1957. Today, organizations and volunteer handlers around the world train dogs for therapeutic work. The results are somewhat amazing.

Therapy dog interactions may lower blood pressure and increase the body's healing capacity.

According to a study abstract published by the UCLA Medical Center, research reported to the American Heart Association in 2005 showed that randomly-selected, hospitalized heart failure patients who received 12-minute visits from a volunteer handler/therapy dog team showed better heart and lung function — attributed to lower blood pressure, reduced anxiety, fewer releases of stress hormones and increases in "good" neurotransmitter levels — than heart failure patients who received a visit only from a human volunteer, or who received no volunteer visit at all.

During the therapy dog visits, specially-trained participating dogs (of 12 different breeds) were allowed to lie on the patients' beds, so that the patient could pet the animal and interact with it while talking to the human volunteer handler.

Researchers measured key indicators of blood pressure, stress hormone levels and anxiety levels before, during and after dog/human team and human-only volunteer interactions, in addition to monitoring the no-visit control group. The results were startling:

• For the dog visit group, self-reported anxiety scores dropped 24% after the visit, as opposed to only a 10% drop for the human-only group and no change for the no-visit control.
• Right atrial pressure in the heart dropped 10% in patients receiving dog visits, whereas it rose slightly in both of the other groups.
• Levels of the stress hormone epinephrine dropped 17% among patients who received dog visits, versus a negligible 2% drop in the human-only group and a 7% rise in the no-visit control group.
• The dog visit group showed more improvements in lung pressure and heart rate than the human-only visit group.

So what's the takeaway?

Good news for dog lovers— the positive benefits that hospitalized patients receive from dog interactions likely extend to the healthy, too. Dog ownership has long been associated with increased longevity, better overall mood and improved cardiovascular health.