Pets are good for your health in numerous ways, including supporting immune function. Clues that dogs may influence the immune system emerged when links to allergies, asthma and eczema, which are due to an over-reactive immune system, were found. For instance, while it was once believed that exposure to dogs (or cats) at birth may increase the risk of allergic disease, it’s now thought that it may decrease it.
Exposure to a dog during pregnancy is associated with a lower risk of eczema in babies by age 2, while allergic proteins and other “elements,” such as bacteria, carried by dogs may have a protective effect on asthma.
It’s likely that early exposure to the diverse bacteria and other microbes from dogs, and possibly cats, benefits infants by helping to prime their immune system to function optimally. Dogs have even been called “the new probiotic” because they give us exposure to a diverse array of dog-borne microbes.
More Exposure to Animal Microbes May Be Beneficial
If you have a dog or cat in your home, it distinctly alters the ecology of bacteria found there. In fact, one study found having a dog significantly elevated 56 classes of bacterial species while having a cat increased 24.
This may be a good thing, as research has previously found that Amish children raised around farm animals had no asthma, compared to Hutterite children raised away from animals, in which asthma developed in 6 out of 30 subjects.
Distinct differences were also found in their innate immune response; the Amish children had a large proportion of neutrophils, which are white blood cells that help heal infections and damaged tissues. “These children’s neutrophils were newly emerged from their bone marrow, evidence of a continual low-grade reaction to microbial invaders,” The New York Times reported.
Among the Hutterite children with asthma, neutrophils were much less abundant. Instead, eosinophils, immune cells that provoke allergic reactions, were plentiful. “It was as if they were primed for an asthma attack as soon as they breathed something to set it off,” according to the Times. While not everyone can live on a farm, some experts believing living with pets is the next best thing.
Pets May Influence Your Gut Bacteria
Many environmental factors influence the makeup of microorganism in your gut, which in turn affect your overall health and immune function. Pets in your home are among them, and it’s been known since the 1980s that pet owners share common intestinal bacteria with their pets.
Further, infants exposed to cats and dogs in early life have greater diversity in their gut microbiome, including increased abundance of Ruminococcus and Oscillospira, which are linked to a reduced risk of childhood atopy and obesity.
A 2020 study that compared the human gut microbiomes of pet owners with non-pet owners also found significant differences in operational taxonomic units (OTUs), which are used to classify groups of closely related bacteria.
According to the researchers, seven OTUs were significantly more abundant in non-pet owners, while four others were elevated among pet owners. It’s unknown what effects this may have on human health, but Jack Gilbert of the University of Chicago told The New York Times, “Exposure to animal bacteria may trigger bacteria in our gut to change how they metabolize the neurotransmitters that have an impact on mood and other mental functions.”
The link between gut microbes and mood in humans is well established, and researchers such as the University of Arizona’s Netzin Steklis have suggested that interactions with dogs that lead to changes in gut microbes may be responsible for some of the mood boosts we get when we spend time around our dogs.
Steklis and colleague Dieter Steklis began a study to determine if pairing older adults with dogs would lead to beneficial changes in human gut microbes that translated to better health.
“It’s always surprised me how many diseases and disorders are linked to inflammatory processes that link back to your immune system,” Dieter told the Tucson Sentinel. “If having a dog actually tames your immune system, which is what it seems to do, then elderly who have a dog may have a lower chance of depressive illnesses.”
Pets Lower Stress Hormones Too
Another way pets influence immune markers is via their role as stress relievers. From lowering blood pressure response to mental stress to increasing levels of the stress-relieving “love hormone” oxytocin, by keeping stress to a minimum your immune health benefits.
“Chronic psychological stress is well known to damage our immune function, compromising our ability to fight off infections while increasing inflammation,” Dr. Austin Perlmutter wrote in Psychology Today. “Pets may be able to help ward off this destructive effect by dampening stress through companionship and the facilitation of social connection with others.”
Researchers with the Indiana University School of Medicine found that even five minutes of interaction with a therapy dog helps lower cortisol levels, a measure of stress, in physicians and nurses working in an ER, and interacting with your pet at home may do so too.
From lowering stress to supporting the health of your gut microbiome and providing beneficial bacteria exposures to prime your immune system against asthma and allergies, the ways pets affect immune function are complex and varied, yet researchers are continuing to shed more light on this important beneficial synergy between humans and their pets.