In a 2022 survey of 3,000 U.S. adults, more than one-third of respondents reported that on most days, they feel “completely overwhelmed” by stress. At the same time, a growing body of research is documenting the negative health consequences of higher stress levels, which include increased rates of cancer, heart disease, autoimmune conditions and even dementia.
Assuming people’s daily lives are unlikely to get less stressful anytime soon, simple and effective ways to mitigate these effects are needed.
This is where dogs can help.
As researchers at the University of Denver’s Institute for Human-Animal Connection, we study the effects animal companions have on their humans.
Dozens of studies over the last 40 years have confirmed that pet dogs help humans feel more relaxed. This would explain the growing phenomenon of people relying on emotional support dogs to assist them in navigating everyday life. Dog owners have also been shown to have a 24% lower risk of death and a four times greater chance of surviving for at least a year after a heart attack.
Now, a new study that we conducted with a team of colleagues suggests that dogs might have a deeper and more biologically complex effect on humans than scientists previously believed. And this complexity may have profound implications for human health.
How stress works
The human response to stress is a finely tuned and coordinated set of various physiological pathways. Previous studies of the effects of dogs on human stress focused on just one pathway at a time. For our study, we zoomed out a bit and measured multiple biological indicators of the body’s state, or biomarkers, from both of the body’s major stress pathways. This allowed us to get a more complete picture of how a dog’s presence affects stress in the human body.
The stress pathways we measured are the hypothalamic-pituitary-adrenal, or HPA, axis and the sympathoadrenal medullary, or SAM, axis.
When a person experiences a stressful event, the SAM axis acts quickly, triggering a “fight or flight” response that includes a surge of adrenaline, leading to a burst of energy that helps us meet threats. This response can be measured through an enzyme called alpha-amylase.
At the same time, but a little more slowly, the HPA axis activates the adrenal glands to produce the hormone cortisol. This can help a person meet threats that might last for hours or even days. If everything goes well, when the danger ends, both axes settle down, and the body goes back to its calm state.
While stress can be an uncomfortable feeling, it has been important to human survival. Our hunter-gatherer ancestors had to respond effectively to acute stress events like an animal attack. In such instances, over-responding could be as ineffective as under-responding. Staying in an optimal stress response zone maximized humans’ chances of survival.
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More to the story
After cortisol is released by the adrenal glands, it eventually makes its way into your saliva, making it an easily accessible biomarker to track responses. Because of this, most research on dogs and stress has focused on salivary cortisol alone.
For example, several studies have found that people exposed to a stressful situation have a lower cortisol response if they’re with a dog than if they’re alone – even lower than if they’re with a friend.
While these studies have shown that having a dog nearby can lower cortisol levels during a stressful event, suggesting the person is calmer, we suspected that was just part of the story.
What our study measured
For our study, we recruited about 40 dog owners to participate in a 15-minute gold standard laboratory stress test. This involves public speaking and oral math in front of a panel of expressionless people posing as behavioral specialists.
The participants were randomly assigned to bring their dogs to the lab with them or to leave their dogs at home. We measured cortisol in blood samples taken before, immediately after and about 45 minutes following the test as a biomarker of HPA axis activity. And unlike previous studies, we also measured the enzyme alpha-amylase in the same blood samples as a biomarker of the SAM axis.
As expected based on previous studies, the people who had their dog with them showed lower cortisol spikes. But we also found that people with their dog experienced a clear spike of alpha-amylase, while those without their dog showed almost no response.
No response may sound like a good thing, but in fact, a flat alpha-amylase response can be a sign of a dysregulated response to stress, often seen in people experiencing high stress responses, chronic stress or even PTSD. This lack of response is caused by chronic or overwhelming stress that can change how our nervous system responds to stressors.
In contrast, the participants with their dogs had a more balanced response: Their cortisol didn’t spike too high, but their alpha-amylase still activated. This shows that they were alert and engaged throughout the test, then able to return to normal within 45 minutes. That’s the sweet spot for handling stress effectively. Our research suggests that our canine companions keep us in a healthy zone of stress response.
Dogs and human health
This more nuanced understanding of the biological effects of dogs on the human stress response opens up exciting possibilities. Based on the results of our study, our team has begun a new study using thousands of biomarkers to delve deeper into the biology of how psychiatric service dogs reduce PTSD in military veterans.
But one thing is already clear: Dogs aren’t just good company. They might just be one of the most accessible and effective tools for staying healthy in a stressful world.
