The study, published in the journal Nature, focused on 58 female dog owners who owned either Shetland sheepdogs or border collies. The researchers studied if stress can synchronize in the long-term between dogs and their owners. They did this by measuring and analyzing the concentrations of cortisol in the hair of both the owner and the dog at two separate occasions, during the summer and winter months. Their analysis found that there was a strong connection between the long-term stress levels of humans and their dogs in both samplings, with the two species' cortisol levels seen to sway up and down alongside each other.
The researchers also conducted surveys to figure out the personality traits of both the dogs and their owners. Along with this, they also monitored the activity levels of dogs for a whole week using activity collars. These additional studies found that the levels of physical activity and training sessions dogs had did not affect the concentration of cortisol in their hair. This suggests that while the attitudes of the dogs had little effect on their stress, the personalities of their humans, such as neuroticism, conscientiousness and openness, significantly did.
Furthermore, the study suggests that dogs who go through a lot of training may be more emotionally reliant on their owners. This means that their emotions are more synchronized to that of their owners.
In figuring out why dogs aren't able to influence the emotions of their people, Dr. Lina S.V. Roth, lead author of the study, believes that this is because of their separate social networks. In an email, Roth states that dogs are more reliant on their humans and are a central part of their lives, while that is not the case with most people. Most people will have other humans as part of their network.
Alicia Buttner, director of animal behavior with the Nebraska Humane Society, expresses mild disagreement. She believes that there isn't enough evidence to assume that the influence can only go one way. "It's not just as simple as owner gets stressed, dog gets stressed," she said, believing that many other factors could affect the stress levels of the person and the dog.
Herself a researcher, Buttner previously studied the short-term synchronization of stress between dogs and humans, particularly between handlers and their dogs during physically demanding agility competitions. Buttner's earlier study provided evidence that Roth's team needed to show the coordination of hormonal changes between the species.
Despite these breakthroughs in understanding the relationship between dogs and humans however, Roth and her team still believe that more research is needed. Particularly, they want to investigate whether this emotional connection extends to other dog breeds to see if this bond truly is universal.
In the meantime, Roth offers her own recommendation to minimize the amount of stress dogs may feel: play. She notes that dogs that spend more time playing show fewer signs of being stressed. "Just be with your dog and have fun," she recommends.