In a 2022 study of 3,000 American adults, more than a third of respondents said they felt “completely overwhelmed” by stress most days.

At the same time, more and more research is documenting the negative health effects of higher stress levels, which include increased rates of cancer, heart disease, autoimmune conditions, and even dementia.

Kevin Morris and Jassie Gandenberger, researchers at the Institute for the Human-Animal Connection at the University of Denver, are studying the effect that pets have on people.

Dozens of studies over the past 40 years confirm that domestic dogs help people feel calmer.

This explains the growing phenomenon of people relying on dogs for emotional support to help them in their daily lives. It has been proven that dog owners have a 24% lower risk of death and a four times greater chance of surviving at least one year after a heart attack.

A new study conducted by Morris and Gandenberger with a team of colleagues shows that dogs may have a deeper and more biologically complex effect on humans than scientists have previously thought. And this complexity may have profound implications for human health.

The human response to stress is a finely tuned and coordinated set of different physiological pathways.

Previous studies on the effect of dogs on human stress have focused on only one pathway.

For this study, the researchers broadened the scope a bit and measured multiple biological indicators of the body's state, or biomarkers, from the body's two main stress pathways. This allowed them to get a more complete picture of how the presence of a dog affects stress in the human body.

The stress mechanisms they measured were the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic-adrenal medullary (SAM) axis.

When a person experiences a stressful situation, the sympathetic medullary axis reacts quickly, triggering a "fight or flight" response that involves a rush of adrenaline, leading to a burst of energy that helps us cope with threats. This response can be measured by an enzyme called alpha-amylase. At the same time, but a bit slower, the hypothalamic-pituitary-adrenal axis activates the adrenal glands to produce the hormone cortisol.

 This can help a person cope with threats that may last for hours or even days. If all goes well, when the danger passes, both axes calm down and the body returns to a calm state.

Although stress is an unpleasant sensation, it is important for human survival. Our hunter-gatherer ancestors had to respond effectively to acute stressful events such as animal attacks. In such cases, an excessive response can be as ineffective as an insufficient response. Staying in the optimal stress response zone increased a person's chances of survival.

Once cortisol is released from the adrenal glands, it eventually ends up in saliva, making it an easily accessible biomarker for tracking responses. For this reason, most studies on dogs and stress have focused solely on cortisol in saliva.

For example, several studies have found that people exposed to a stressful situation have a lower cortisol response if they are with a dog than if they are alone—even lower than if they are with a friend.

Although these studies have shown that having a dog nearby can lower cortisol levels during a stressful situation, suggesting that the person is calmer, researchers suspect that this is only part of the story.

For this study, they recruited about 40 dog owners to participate in a 15-minute gold standard laboratory stress test. It involved public speaking and verbal math tasks in front of a group of people posing as behavioral experts.

Participants were randomly assigned to bring their dogs to the lab or leave them at home. The researchers measured cortisol in blood samples taken before, immediately after, and about 45 minutes after the test as a biomarker of HPA axis activity. And unlike previous studies, they also measured the enzyme alpha-amylase in the same blood samples as a biomarker of SAM axis activity.

As expected based on previous studies, people who brought their dogs showed lower cortisol peaks. But we also found that people with their dogs had a clear peak in alpha-amylase, while those without dogs showed almost no response.

The lack of response may sound like a good thing, but in fact, a flat alpha-amylase response can be a sign of a disrupted stress response, often seen in people who experience intense stress reactions, chronic stress, or even post-traumatic stress disorder. This lack of response is caused by chronic or excessive stress, which can alter the way our nervous system responds to stressors.

In contrast, participants with dogs had a more balanced response: their cortisol levels did not rise excessively, but their alpha-amylase was still activated. This shows that they were alert and engaged throughout the test and were able to return to normal within 45 minutes. This is the ideal scenario for effective stress management.

This study shows that our canine friends keep us in a healthy stress response zone. | BGNES