Studies show dog owners live longer. Why?

Hugging a dog is one life's greatest joys. Getting to see fur on four legs and a wagging tail is like experiencing a love drug — quite literally.

Dogs and humans that interact with one another get a jolt of oxytocin, the so-called "cuddle hormone." And, if you get to look at dogs and hug them every day, you just might live longer than people who don't have to clean animal hair off their clothes, according to a pair of studies out this month.

The studies, published in the journal Circulation: Cardiovascular Quality and Outcomes, suggest that dog ownership is linked to a 21 percent reduction in the risk of death — over the 12-year period studied — for people with heart disease. Those studies complement a body of literature linking dogs to good health.

Dr. Dhruv Kazi, a cardiologist and health economist at the Beth Israel Deaconess Medical Center and Harvard Medical School, wrote an accompanying editorial for the new studies but was not involved with the research.

"When you look at the big picture and look at all the evidence around dog ownership and cardiovascular health, it's pretty clear the signal is real and likely causal," he says.

In other words, he's convinced getting a dog improves your health — especially for those with heart disease.

The research is not definitive, though, Kazi adds.

"They're not randomized trials, the gold standard for what we would do to evaluate a new drug," he says.

Ideally, Kazi says, researchers would conduct an experiment where 1,000 people get a dog and 1,000 people get a stuffed animal. Then the researchers would try to measure how their health changed afterward. Instead, these studies looked at data from dog owners and people without pets from national registries in Europe.

WBUR spoke with Kazi about dogs, their effect on health and why you might want to consider becoming a dog person.

This interview has been edited for length and clarity.

What have researchers observed in the past when it comes to the health benefits of dog ownership?

We've known forever that owning a dog increases one's physical activity. Regardless of weather, you have to get out and walk the dog. Otherwise, you might be tempted to stay home and watch TV.

There are other effects that we've known for a while. There is the idea that owning a dog makes you spend more time outdoors, and time spent outdoors improves health and, specifically, cardiovascular health.

But I think the biggest advantage of having a dog is what it does for mental health. We see very beneficial effects on depression, on anxiety, etc.

We've had programs where therapy dogs walk through the residency rooms and interact with patients. You see people light up. Unless you have a friend or family member by you all day, it's an incredibly lonely experience in the hospital. To have this animal walk by and, you know, offer you its unconditional love. That tail wag has the ability to make that day, and I see that all the time in the hospital.

Owning a dog or interacting with a dog even for a short term reduces blood pressure, improves your cholesterol profile. All of these taken together, we imagine, would improve cardiovascular health.

These two most recent studies suggested that dog ownership reduces the risk of death from any cause for people with cardiovascular disease — not just heart attacks. What did they do in these studies?

In one case, it was what we call a meta-analysis. It looked at all prior literature on dog ownership and heart health and showed there's an effect of dog ownership on mortality from any cause and cardiovascular mortality.

In another study, [researchers] looked over a 12-year period at dog owners in Sweden who have cardiovascular disease. They adjusted for the kinds of things we know affect cardiovascular health — age, demographics, socioeconomic status, marital status, number of children at home — and even after adjusting for all of that, they found a benefit of dog ownership.

How much was that benefit?

In the Swedish study, they followed over 100,000 people and found a 21 percent reduction in deaths from any cause. In particular, I found it very convincing and striking that the benefits seems to be larger among individuals who live alone compared to multiperson households. That suggests the companionship of a dog is possibly very important to their heart health.

That seems like a massive benefit, doesn't it?

Yeah. You know, I'm reluctant to hang my hat on that number because it may be that some of the effect is because healthier people own dogs, and etc. Well, let's say it's 15 percent, not 21 percent. That's an intervention that is relatively low risk and could have a substantial mortality benefit.

Doctors should feel comfortable discussing dog ownership with their patients in the right setting. In individuals who are able to — this is a therapy worth trying. But you also wouldn't get a dog just for cardiovascular health. In the end, you have to have the space in your life to accommodate an animal and a friend.

But I think that Americans have generally internalized the benefits of having a dog. At this point, there are more pet dogs in the U.S. than kids under the age of 18.

Or maybe they've internalized the health consequences of having kids.

Right, [laughs]. That could be true, too.

Do you have a dog yourself?

I don't, but I've wanted one for 40 years. I think these studies have finally convinced me to get one. I think we've thought of dogs as a form of comfort, a luxury even. For me, the study forces a rethinking of pets in our society. We've started out with dogs as accomplices during hunts as hunter-gatherers.

Gradually, we selected for traits of loyalty and friendship. At this point, society — particularly Western society — is very individualistic and fragmented. I can totally see the rationale for why dogs improve our sense of well-being, reduce loneliness, improve self-esteem and can be a boost to our physical and mental health.

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