Research suggests that bonding with dogs can reduce depression and anxiety

They’re said to be our best friends, and a new study suggests there might actually be a mental health dividend for pet owners who feel a genuine connection with Fido.

Researchers from the Harvard Nurses’ Health Study, examining the conflicting evidence on whether owning a pet is good for our mental health, found that owning — and loving — a dog (sorry, cat lovers) is associated with reduced symptoms of depression and anxiety.

The Gazette spoke with Eva Schernhammer, a nurse health researcher and assistant professor of epidemiology at the Harvard T.H. Chan School of Public Health, about the research, recently published in Opening of the JAMA network.

Schernhammer said this work is a first step in uncovering the connections between ourselves, our physical and mental health and the pets we keep.

What did you find?

We used several different measures of depression and anxiety and found overall that there is an inverse association between pet attachment and negative mental health outcomes. This means that the more attached you are to your pet, the less likely you are to suffer from depression and anxiety.

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

I think these results were mainly attributed to dogs, because the majority of pets studied were dogs: about two-thirds were dogs and one-third were cats. The association was similar to what we found when we restricted the analysis to dogs only, but not as strong.

When it comes to cats, there does not appear to be a link between attachment to animals and mental health outcomes. However, given the smaller number of respondents, we cannot rule out that we did not find anything because there were too few cats in the survey.

I think we were all a little surprised to find that there is such a difference between dogs and cats. It will be interesting to explore this in more detail.

Is this a topic you have been studying for some time?

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

There have been many studies on the effects of pet ownership, but the premise of this study is that the degree of attachment to the pet may be more important than simply owning one. Many people have pets, but not all owners are attached to their pets.

Many people don’t like walking their dog in the morning because the dog is their child’s favorite pet, for example. So the goal was to determine whether attachment is the most important variable linking pets to health outcomes in humans, and then to study the mechanisms.

We have completed, to some extent, the first part of this project and are now beginning to examine the mechanisms that might explain why stronger attachment to pets might be linked to better mental health outcomes in these cohorts. The main hypothesis is that this might be mediated by the microbiome and metabolomics.

We are just beginning to look into this issue and we have discovered in the article we are discussing that there is a big difference between dogs and cats. This was not entirely expected, but it is obvious.

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

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

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

The Mind Body Study captured many different aspects of participants’ psychosocial context, including attachment to pets, which is not typically assessed. So this gives us a rare opportunity to examine this topic.

They also provided two blood and urine samples, which was pretty much it, at the beginning of the study and a year later. And because the study focuses 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, whether sexual or physical.

You mentioned a follow-up study on the microbiome as a potential mechanism for these effects. What did you look at? Were stool samples taken?

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

We have started collecting stool from participants and their pets. This means we have simultaneous samples from both the owner and their cat or dog. We want to analyze these to look for specific patterns in the microbiome that have been previously observed in people with depression.

Perhaps we will see these patterns diverge between domestic dogs and cats, for example, which could explain the information about lower risk of depression. By looking at concurrent owners and their pets’ stools, we can also see if there is microbial transfer going on, altering their risk of depression.

I always thought that the positive benefits of owning a pet were due to the companionship and affection they provide, but could it all come down to physical and biological reasons?

Yes, we want to understand if there are biological mechanisms that we can explore. This makes sense, because even for some of the psychosocial variables in humans that have been linked to health problems, typically when you start studying them, they also have an impact on biology.

Stress, for example, can change your sensitivity to glucose intake. So it wouldn’t be surprising if, even though this is mainly due to psychosocial factors, these translate into something more mechanical. This is something very tangible and it could also explain why, for example, it might be different for cats, because most cats are indoor cats. This is also what we’re going to look at, whether there are big differences between the microbes that we find in dog feces and cat feces.

Is the take-home message that everyone should have a dog? Cat owners might not appreciate that.

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

It also helps us better understand this subgroup of women who experienced childhood abuse. They made up the vast majority of our sample, and I think that’s an important point to make. I hope there will be more well-conducted studies that shed light on this topic.

This is an interesting avenue that could do something for human mental health and, at the same time, increase physical activity and change other aspects of our lives that are affected by pets. We are just beginning to understand the benefits of pets, and this could be an important step.

This article is reprinted courtesy of the Harvard Gazette, the official newspaper of Harvard University. For more information about the university, visit Harvard.edu.