P. Elizabeth Anderson once had a daughter named Grace. Like any parents would, she and her husband cared for her, nurtured her and tried to keep her out of trouble. They took her on vacations and enjoyed her company around the house. “She was my constant companion,” says Anderson, a journalist in the District of Columbia.

So when Grace died unexpectedly at age 14, the couple was crushed. But because Grace was a dog, “I was unable to talk to anyone about this immense grief,” says Anderson, who wrote the book “The Powerful Bond between People and Pets: Our Boundless Connections to Companion Animals.”

The depth of Anderson’s devastation surprised her, but it’s common to feel that way after the loss of a dog, says Lori Kogan​, associate professor of clinical sciences at Colorado State University's College of Veterinary Medicine and Biomedical Sciences. Some people feel so sad, in fact, that they wonder if the death of a human companion would have been easier. “People feel guilty because they feel worse when their dog dies than if a family member dies,” Kogan says. “And then they think they’re a bad person.”

But in reality, it’s normal. “There’s a reason you feel that way,” she says. One of them? Unlike the mixed feelings we have toward each other – and that arise after a person's death – "our relationship with dogs is so uncomplicated," Kogan says. Some might​ call it​ true love.

Puppy Love

Research suggests the connection many humans feel with their canine companions is a lot like love. In one recent study in the journal Science, for instance,​ researchers found the same hormone associated with maternal love and passionate love, oxytocin, increases in both pups and their owners when the two species do ​no more than lock eyes. The same can’t be said for humans and wolves, the researchers found. The results suggest "a coevolution between human and dogs," says lead study author Takefumi Kikusui, a professor in the Department of Animal Science and Biotechnology at Azabu University in Japan. That's part of the reason why, he says, "it is very natural to form a bond between dogs and humans."

Stanley Coren​, a professor emeritus in the University of British Columbia's department of psychology says dogs are a man’s best friend because we’ve domesticated them to be that way.

“We invented the dog and we invented it to fit in a certain niche in our lives,” says Coren, who's written a series of popular books on pooches. “And so for at least 14,000 years, we have been … creating an animal which understands our communications and we understand its communications and they have a bond with us.” For example, if a person points to something in a distance, a dog will look in the direction of the finger, just like a human. But if the dog was a wolf? It would simply look at the finger, Coren says. “We’ve sort of wired the dog to read our communications,” he says.

For Anderson, who’s now a mother to a Maltese and a Yorkie, dogs can be more lovable than humans because "they absolutely go out of their way to please us,” she says. “They want to do whatever we want to do, their love is absolutely unconditional, they’re affectionate to a fault – all the kinds of things that humans enjoy in a relationship are the kinds of things dogs excel at.”

‘Instant Prozac’

Over 54 million U.S. households own more than 77 million dogs, according to the American Pet Products Association. And those pups are pampered: Dog moms and dads spend $83 on grooming, $47 on toys and $330 on food and treats for their furry children each year, according to the association’s most recent survey of pet owners. "We have completely embedded pets into human culture," Anderson says.​ “We give our dogs human names, dress them up for holidays, give them gifts, take them to church and grieve deeply when they die.”

Is that healthy? By most accounts, yes. Studies have shown, for instance, that simply petting “a familiar and friendly” dog can lower your heart rate, make your breathing more regular and relax your muscles, ​Coren says. In one unpublished study, people had significantly lower blood pressure just two months after adopting dogs when compared to pet-parents-to-be who were still waiting for their puppies, reports the American Heart Association. The organization concludes that owning a dog "may have some causal role" in reducing heart disease risk.

Recent research has emphasized how dogs can​ reduce stress and boost mental health. A 2012 study in the International Journal of Workplace Health Management of ​a 550-employee company found that workers’ stress levels declined over the course of the day if they brought their dogs to work. The opposite was true for dogless employees and those who left Rover at home.

“We know that stress and all those nasty things do bad things for our health” such as weakening our immune system and putting our hearts at risk for cardiovascular problems, Coren says. One answer could be right under our snouts. “Dogs that act like instant Prozac.”

Can you love your dog too much?

It’s feasible your attachment to your furry friend could go too far. “Just as you can have unhealthy relationships and attachments to people, you can have unhealthy attachments to pets,” Kogan says.

Say, for example, you use your dog as an excuse to isolate yourself from humans. “If you don’t have anyone in your life, that’s a red flag,” Anderson says. Research shows that weak social connections can be detrimental to physical and mental health, even making you twice as likely to die than being obese, a 2010 meta-analysis found.​ What’s more, Coren adds, “the absence of social support is one of the major contributors to depression.”

The good news? Dogs seem to have a similar effect on health as human companions. A 2011 study found that pet owners had better self-esteem, were in better shape and felt less lonely than people without pooches or other pets. It makes sense, Coren says. Simply taking your dog for a walk, for one, facilitates fitness – and human interaction. “You’re marching along with your version of Lassie, and [someone else is]​ walking along with their version of Benji and you stop to chat,” he says.