Research suggests that connecting with dogs can reduce depression and anxiety

They’re considered our best friends, and new research suggests that pet owners who feel a real bond with Fido may even have a positive effect on their mental health.

Researchers from Harvard’s Nurses’ Health Study, who examined conflicting findings about whether having a pet is good for our mental health, found that owning a dog (and loving a dog, sorry, cat people) is linked to fewer symptoms of depression and anxiety.

The Gazette spoke with Eva Schernhammer, a researcher in the Nurses’ Health Study and associate professor of epidemiology at the Harvard TH Chan School of Public Health about the researchrecently published in JAMA Network Opened.

According to Schernhammer, the work is a first step in discovering the connections between ourselves, our physical and mental health, and the pets we keep.

What did you find?

We used different measures of depression and anxiety and found that overall there is an inverse association between pet attachment and negative mental health outcomes. That means the more attached you are to your pet, the lower your risk of depression and anxiety.

The effect was particularly strong among women with a history of childhood sexual or physical abuse, who constituted the majority of our study population.

I think those findings were driven by dogs in particular, because the majority of the pets in the study were dogs – it was about two-thirds dogs and one-third cats. The association was similar to what we found when we restricted the analysis to just dogs, but not as strong.

In cats, there appears to be no association between pet attachment and mental health outcomes. However, there was a smaller number of respondents, so we cannot rule out that we are not seeing anything because there were too few cats in the survey.

I think we were all a little surprised that there was such a big difference between dogs and cats. It will be interesting to investigate this further.

Is this a topic you’ve been thinking about for a while?

This is part of a larger study of human-animal interactions, particularly with pets. We felt that this was understudied, and there was a great opportunity to explore it in the Nurses’ Health Study cohort. It’s also something that people are happy to share: it turns out that the nurses in the study were more than willing to share interesting details about their pets.

There have been many studies on the effects of pet ownership, but the premise of this research is that it may be more important how attached you are to your pet than if you just have a pet. Many people have pets, but not every owner is attached to their pet.

Many people don’t like having to walk their dog in the morning, because the dog is their child’s beloved pet, for example. So the goal was to find out whether attachment is the key variable linking pets to health outcomes in humans, and then to study mechanisms.

We have completed the first part of this project to some extent and are now starting to look at mechanisms that might explain why higher pet attachment might be linked to better mental health outcomes in these cohorts. The primary hypothesis is that this might be mediated by the microbiome and metabolomics.

We just started looking at this and the finding – in the paper we’re reviewing – that there’s a big difference between dogs and cats. That wasn’t exactly expected, but it’s stark.

Interestingly, in our preliminary metabolomics analysis we see quite different patterns between cats and dogs. It will be interesting to understand whether some of these putative microbiome mechanisms indeed differ between cats and dogs and whether this could explain what we see in this first paper.

That’s interesting. So in the Nurses’ Health Study II, the cohort that you’re using, were biological samples taken?

Yes, but this cohort comes from a substudy, the Mind Body Study, which was done about 10 years ago. The goal of that study was to look more closely at psychosocial factors, which was not the main focus of the Nurses’ Health Study, which was started to study breast cancer risk and lifestyle factors.

The Mind Body Study captured many different aspects of participants’ psychosocial contexts, and one of them was pet attachment, which is not normally assessed, so it gives us a rare opportunity to look at that.

They also provided two samples of blood, urine — basically everything — at the beginning of the study and a year later. And because of the focus on psychosocial aspects, they also oversampled women who had experienced some form of childhood abuse. About three-quarters of the women in this cohort had experienced some form of abuse, either sexual or physical.

You mentioned a follow-up study of the microbiome as a possible mechanism for these effects. What did you study? Were stool samples taken?

There are stool samples. We have a study — we’re trying to get funding to do additional analyses — the Nurses’ Health Study 3, which is still recruiting and online. We started by surveying pets, because it’s pretty easy to send questions to participants with online questionnaires.

And we’ve started collecting stool samples from the participants and their pets. That means we have simultaneous samples from both the owner and their cat or dog. We want to analyze them to look for specific patterns in the microbiome that have been shown in depressed individuals.

Perhaps we see that those patterns differ between, say, dogs and cats, which could explain the information about the lower risk of depression. By looking at concurrent owners and their pets’ feces, we can also see if there’s microbial transfer that’s changing their risk of depression.

I always thought that the positive effects of having a pet were due to the companionship and affection they provide, but could it all have to do with physical and biological reasons?

Yes, we want to understand if there are biological mechanisms that we can investigate. That makes sense because even for some psychosocial variables in people that have been associated with health outcomes, they usually also have an impact on biology when you start looking at it.

Stress can change your susceptibility to glucose intake, for example. So it wouldn’t be entirely surprising, even if this is driven primarily by psychosocial factors, that those translate into something more mechanistic. That’s something very tangible and could also explain why this might be different for cats, for example, since most cats are indoor cats. That’s also part of what we’ll be looking at, is whether there are big differences between the microbes that we find in dog feces and cat feces.

Is the message that everyone should get a dog? Cat owners may not like that.

Also, the cats may not like it. An important message is that in our subgroup of women who were abused, these findings were particularly strong. Perhaps in the future we can define more subgroups who might benefit from having a pet. We shouldn’t prescribe a pet for someone who doesn’t like animals, but if someone wants a pet and can accommodate one in their living environment, then this might be a good way to manage depression-related symptoms.

This also helps us to better understand this subgroup of women who were abused in childhood. They were the vast majority in our sample, and I think that’s an important point to make. I really hope that there are more well-conducted studies that shed light on this.

It’s an interesting potential way to help people’s mental health while also increasing physical activity and changing other aspects of our lives that are affected by pets. We’re just beginning to understand the benefits of pets, and this could be an important step.

This story is published with thanks to the Harvard Gazettethe official newspaper of Harvard University. For more university news, visit Harvard.edu.