A dog is man's best friend in the most ordinary situations, but it's when you're down and out that your canine partner really comes through in the clutch. From easing military veterans' battles with post-traumatic stress disorder to reducing heart and lung pressure for heart-failure patients, the tail-wagging beasts are walking therapy centers. They're also great motivators to get you off the couch and exercise, and can even improve infant immune systems. Here, eight ways dogs improve our health:

1. Lessen the side effects of chemotherapy
Once a week for the past seven years, Veronica Pardo, a volunteer, has brought two dogs to the only hospital in Quito, Ecuador, that treats children with cancer. The dogs not only "bring a sparkle to the eyes and smile to the faces of little ones in the midst of a huge struggle to stay alive," says The Associated Press, they also have been shown to boost the children's adrenaline, which helps them bolster their resistance to the harsh effects of chemotherapy.

2. Help veterans with PTSD
Many veterans from the wars in Iraq and Afghanistan suffer from chronic fear, anxiety, depression, and other forms of post-traumatic stress disorder, and dogs are ideal companions to "draw out even the most isolated personality" and help "traumatized veterans overcome emotional numbness," says Chris Coling at Smithsonian Magazine. There are currently four experimental programs nationwide in which PTSD-afflicted veterans are paired with Labradors and Golden Retrievers as therapy.

3. Strengthen babies' immune systems
"Dander particles, fuzzy fur, hardballs accumulating in corners," says Leah Zerbe at Rodale: "Everything about owning a pet suggests breathing problems," particularly for children. However, a Finnish study shows that "babies living in a home with a dog were generally healthier, suffered fewer respiratory and inner ear infections, and required fewer antibiotics in their first year of life." Scientists theorize that dogs bring an array of germs into the house, and the additional exposure strengthens babies' immune systems.

4. Relieve student stress
Universities around the country are employing dogs during exams in order to help stressed-out students "relax and maybe even crack a smile or two," says The Associated Press. Dogs are "in counseling centers for students to visit regularly," and "pet-friendly dorms also are popping up where students can bring their dogs or cats from home." Harvard Medical School and Yale Law School even allow students to "check out" resident "therapy dogs" from libraries. 

5. Get people exercising
"If you're looking for the latest in home exercise equipment, you may want to consider something with four legs and a wagging tail," says Tara Parker-Pope at The New York Times. Studies show that dogs "can be powerful motivators to get people moving" and take daily walks. One study shows that "among dog owners who took their pets for regular walks, 60 percent met federal criteria for regular moderate or vigorous exercise," compared with about 30 percent for those who didn't have dogs.

6. Help autistic kids
A recent French study shows that "getting a pet may help children with autism to develop their social skills," says MyHealthNewsDaily, as long as "the furry friend is brought into the home when the child is about 5 years old." The researchers found that "children with autism who got a pet after age 5 showed improvement in their abilities to share with others and to offer comfort, whereas those who had a pet since they were born, and those who never had a pet, showed no such improvement."

7. Heal the heart
A new study shows that therapeutic dogs can "lower anxiety, stress, and heart and lung pressure among heart-failure patients," says Jamie Stengle at The Associated Press. According to researchers, "heart pressure dropped 10 percent" for patients after a visit from a human volunteer and a dog, while it increased 3 percent when only the volunteer showed up and climbed 5 percent with no visit at all. 

8. Sniff out cancer
German researchers have reported that dogs can reliably detect lung cancer just by smelling human breath. Four dogs in the study were able to sniff out lung cancer in 71 out of 100 breath samples from lung-cancer patients, while correctly identifying cancer-free breath samples 91 percent of the time.

Sources: The Associated Press (2) (3), MyHealthNewsDailyThe New York TimesRodaleSmithsonian Magazine