In a survey conducted in 2022 to 3,000 American adults, more than a third of respondents claimed to feel overwhelmed by stress most of the days. At the same time, more and more research document the negative consequences for the health of high levels of stress, such as the increase in cancer rates, heart disease, autoimmune diseases and even dementia.
Since it is unlikely that people’s daily life becomes less stressful in the near future, simple and effective methods are needed to mitigate these effects.
This is where dogs can help.
As researchers from the Institute for Human-Animal Connection of the University of Denver, we study the effects that pets have on their humans.
Dozens of studies in the last 40 years confirmed that dogs help humans feel more relaxed. This would explain the growing phenomenon of people who resort to emotional support dogs to face everyday life. It was also shown that dog owners have 24% less risk of death and four times more likely to survive at least one year after a heart attack.
Now, a new study that we did with a team of colleagues suggests that dogs could have a deeper and biologically complex effect on humans of what scientists previously believed. And this complexity could have deep implications for human health.
How does stress work?
The human response to stress is a set of various perfectly coordinated and tight physiological pathways. Previous studies on the effects of dogs on human stress focused on one way at a time. For our study, we expand the information and measure multiple biological indicators of the body state, or biomarkers, of the two main stress routes of the body. This allowed us to obtain a more complete image of how the presence of a dog affects stress in the human body.
The stress routes that we measure are the hypothalamus-hypo-adrenal (HPA) axis and the sympathetic-medular axis (SAM).
When a person experiences a stressful event, the Sam axis acts quickly, triggering a response of “struggle or flight” that includes an adrenaline discharge, which generates an explosion of energy that helps us to face threats. This answer is measured by an enzyme called Alfa-Amilase.
At the same time, but at a slightly slower pace, the HPA axis activates the adrenal glands to produce the cortisol hormone. This can help a person to face threats that can last hours or even days. If everything goes well, when the danger ceases, both axes are stabilized and the body returns to its state of calm.
While stress can be an uncomfortable sensation, it was fundamental for human survival. Our ancestors hunter-gatherers had to respond effectively to acute stress events, such as the attack of an animal. In such cases, an exaggerated response could be as ineffective as an insufficient response. Staying in an optimal area of response to stress maximized the possibilities of survival of humans.
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How can dogs reduce stress in humans?
After the release of cortisol through the adrenal glands, it reaches saliva, becoming an easily accessible biomarker for the monitoring of the answers. Therefore, most research and stress research has focused solely on salivary cortisol.
For example, several studies have discovered that people exposed to a stressful situation present a lower cortisol response if they are with a dog that is alone, even lower than if they are with a friend.
While these studies have shown that having a close dog can reduce cortisol levels during a stressful situation, suggesting that the person is quieter, we suspected that this was just part of the story.
What did the study measure?
For our study, we recruit about 40 dog owners to participate in a 15 -minute laboratory stress test, the reference test. This test is to speak in public and perform oral calculations in front of a panel of inexpressive people who go through behavior specialists.
The participants were randomly assigned to bring their dogs to the laboratory or leave them at home. We measure the cortisol in blood samples taken before, immediately after and approximately 45 minutes after the test as a biomarker of the HPA axis activity. Unlike previous studies, we also measure the alpha-amylase enzyme in the same blood samples as Sam axis biomarker.
As expected, previous studies, the people who took their dog showed lower cortisol peaks. However, we also observed that those who took their dog experienced a clear peak of alpha-amylase, while those who did not carry it did not show an answer.
The absence of response may seem positive, but in fact, a flat alpha-amylase response can be a sign of a deregulated response to stress, which is often observed in people who experience high-stress responses, chronic stress or even PTSD. This lack of response is due to chronic or overwhelming stress that can alter the way in which our nervous system responds to stressful factors.
Instead, participants with their dogs had a more balanced response: their cortisol did not shoot too much, but their alpha-amylase was activated. This shows that they were alert and concentrated throughout the test, and then returned to normal in 45 minutes. That is the optimal point to handle stress effectively. Our research suggests that our canine classmates keep us in a healthy area of stress response.
Dogs and human health
This more detailed understanding of the biological effects of dogs on the human response to stress opens new possibilities. Based on the results of our study, our team has started a new study with thousands of biomarkers to deepen the biology of how psychiatric service dogs reduce the PTSD in military veterans.
But something is already clear: dogs are not only good company. They could be one of the most accessible and effective tools to stay healthy in a stressful world.
With information from The Conversation
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