A dog's stress level throughout its lifetime may be linked to the stress level of its owner, according to a study published recently in Scientific Reports.
The human-canine connection
Dogs and humans have been living together for about 15,000 years, and during that time, the two developed a mutual affection and dependence that allows them to establish a serious emotional bond, according to the Los Angeles Times.
This connection has proven beneficial to humans. For instance, one study found that dog owners live longer and are healthier than people without dogs.
But the psychological bond can affect dogs, too—and not always in good ways.
For the latest study, researchers set out to determine how dogs' stress levels relate to those of their own human companions. To do that, researchers in the study analyzed the stress levels of 33 Shetland sheepdogs and 25 border collies and their human owners. Researchers measured stress level by looking at the level of cortisol, the stress hormone, in the dog's and human's hair.
The researchers also asked the human participants to fill out questionnaires that measured their temperament and that of their dog. This allowed researchers to explore whether there was an association between the dogs' temperaments and their stress levels.
Dogs pick up on our stress
The study found a "clear" association between the dogs' stress levels and their owners' stress levels.
The cortisol levels in both dog breeds were high when their humans' stress levels were high, the study found. Similarly, dogs whose owners had lower levels of cortisol were less likely to experience chronic stress.
In addition, the researchers found certain factors may make some dogs even more likely to take on their human friends' stress. For instance, female dogs were more likely to mirror the stress levels of their human owners than male dogs, and dogs that were training for a competition were more likely to be impacted by their owner's stress level than non-competitive canines.
However, the researchers found no association between canine cortisol levels and whether the owner worked outside of the house during the week, which served as "comforting news" for dog owners who spend most of the week separated from their furry companions, the Times reports.
Perhaps surprisingly, the researchers found no relationship between a canine's cortisol levels and its temperament. In fact, according to the researchers, an owner's stress level was a stronger predictor of a dog's stress level than the dog's personality. As such, the researchers wrote, "It is the dogs that mirror the stress levels of their owners rather than the owners responding to the stress in their dogs."
The researchers also determined that there is no significant alignment between the temperaments of dog owners and their pets.
Jonathan Santo, a developmental psychologist at University of Nebraska at Omaha, said, "What this paper seems to hint at is some of the underlying mechanisms behind why humans and dogs or wolves have been able to domesticate each other over thousands of years." Santo added that he believes the dogs' stress levels may impact their owners' stress levels as well, but said he's "inclined to believe" that dogs are more sensitive to human stress. "It makes sense as an evolutionary strategy that they have become very sensitive to humans, and adopted properties that endear them to us," he said.
Meanwhile, Brian Hare, a professor of evolutionary biology at Duke University, said the findings only show an association between humans' stress levels and dogs' stress levels. He said additional research is needed to determine whether or not an owner's stress level is the main predictor of stress in their dogs.
Lina Roth, senior author of the study and a dog owner, said the team is already planning follow-up studies to better assess the long-term emotional synchrony between dogs and humans. In the meantime, Roth advises that dog owners avoid bringing stress home with them. "If we just interact with the dog in a positive way, we do give the dog what it wants. Have fun with your dog" (Healy, Los Angeles Times, 6/6; Hersher, "Shots," NPR, 6/6).