Good for Mind and Soul

Pet owners with AIDS are far less likely to suffer from depression than those without pets. "The benefit is especially pronounced when people are strongly attached to their pets," says researcher Judith Siegel, PhD.

In one study, stockbrokers with high blood pressure who adopted a cat or dog had lower blood pressure readings in stressful situations than did people without pets.

People in stress mode get into a "state of dis-ease," in which harmful chemicals like cortisol and norepinephrine can negatively affect the immune system, says Blair Justice, PhD, a psychology professor at the University of Texas School of Public Health and author of Who Gets Sick: How Beliefs, Moods, and Thoughts Affect Your Health.

Studies show a link between these chemicals and plaque buildup in arteries, the red flag for heart disease, says Justice.

Like any enjoyable activity, playing with a dog can elevate levels of serotonin and dopamine—nerve transmitters that are known to have pleasurable and calming properties, he tells WebMD.

"People take drugs like heroin and cocaine to raise serotonin and dopamine, but the healthy way to do it is to pet your dog, or hug your spouse, watch sunsets, or get around something beautiful in nature," says Justice, who recently hiked the Colorado Rockies with his wife and two dogs.