Newborns who live in a home with cats or dogs appear to be less likely to develop food allergies, according to the findings of a large study. The benefit holds even if the exposure is during foetal development, when a pregnant mother lives with pets.
The effect in the study was modest but statistically significant: exposure to dogs or cats during foetal development or the first few months of life lowered the odds of a later food allergy by about 14%. The benefit was strongest when the dogs were kept indoors and when the exposure was during both foetal development and infancy.
Earlier studies reached similar conclusions, but the new study from Japan, involving more than 65 000 infants and their parents, is by far the largest to date. Like other studies, this one could not prove that pets themselves lower the risk of a food allergy. It could be that something else associated with pet ownership, such as lifestyle or genetics, could be causing the apparent association.
But paediatricians who specialise in the study and treatment of allergies said the results look reassuring for pet owners.
“The finding that exposure to dogs and cats is related to less food allergy seems pretty solid and agrees with several prior studies,” said James Gern, professor and chief of the Division of Allergy, Immunology and Rheumatology at the University of Wisconsin at Madison.
Gern, who published a paper in 2004 showing that dog ownership reduces the risk of all kinds of allergies, said the new study “adds to the growing literature that contacts with pets could have many health benefits for children. In addition to food allergy, other studies have found lower rates of atopic dermatitis, wheezing illnesses, respiratory allergies, asthma and increased psychological well-being.”
The new study, published in the open-access journal “PLoS ONE”, was led by Hisao Okabe of the department of paediatrics at the Fukushima Medical University. She and colleagues analysed data for the Japan Environment and Children's Study, a nationwide study of all pregnancies between January 2011 and March 2014. Information was obtained from medical records and self-administered questionnaires. The researchers examined children’s risk of developing food allergies up to age 3.
Okabe and colleagues checked pet ownership’s link to food allergies overall, as well as to a variety of specific food allergies. Dog ownership, they found, reduced the risk of egg, milk and nut allergies, while cat ownership reduced the risk of egg, wheat and soya bean allergies.
The study also looked at possible effects from other pets. No significant association was seen between food allergies and exposure to turtles, hamsters or birds. But when the link was limited to nut allergies only, hamster ownership actually increased the risk by 93%. So few families kept hamsters, however, that the apparent association could be a statistical fluke.
The lowered risk of developing food allergies due to living with dogs was far less in the present study than in a paper published in 2019. That study, which directly tested young children for food allergies rather than relying on parents’ questionnaires, found that living with dogs reduced the odds of developing a food allergy by an extraordinary 90%. And the more dogs the better: none of the infants who lived with at least two dogs developed a food allergy.
The senior author of that study, Tom Marrs, director of the Allergy Academy at King’s College London, said that while only about 7% of children in the UK have a food allergy confirmed by testing, up to a quarter of parents nevertheless say that their kids have such an allergy. The study out of Japan would have benefited by directly testing the young children with food challenges, he said.
Another limitation of the study, Marrs said, is that it can’t prove that the pets themselves, rather than something about the pet owners, are the true cause of the lowered odds of food allergies.
“Families with a strong family history of allergy are likely to have parents with pet-dander allergies,” Marrs said. “This makes it less likely that they will get pets for their children. So the inverse relationship between pets and allergies may be owing to the allergic parents not wanting to react to pets themselves.”
The only way to prove that pet ownership reduces the risk of food allergies, he said, is with a randomised controlled trial, in which pregnant women agree to be randomly assigned to either have a pet or not. But, he said, it would be difficult to find people willing to participate in such a study.
Amanda Cox, a professor of paediatrics at the Jaffe Food Allergy Institute in the Icahn School of Medicine at Mount Sinai in New York, said that parents routinely ask her whether pets raise or lower their children’s risk of developing allergies. “I definitely would say it’s been a murky area, but this study looks fairly convincing,” she said of the Japan study.
A review published last year of all the proven ways to reduce the development of allergic disease included breast-feeding exclusively for the first four to six months after birth; avoiding cows’ milk during the first days of life; introducing peanuts in an age-appropriate manner if the family usually eats them; and growing up on a farm (due to exposure to a greater diversity of microbes). That same review cautioned that when parents or siblings have allergies, or when the child already has atopic dermatitis, families should avoid acquiring a cat.
“If I see a kid who has significant eczema, and I know they have a cat or dog in the house, I might have them tested for being allergic to those pets,” Cox said.
Because the study out of Japan was undertaken well before the Covid-19 pandemic, Cox said: “I would be interested in knowing whether spending more time inside with pets during the pandemic increased the effect on children’s allergies.”
The large size of the study could have actually led the investigators to find apparent spurious statistical links when drilling down to particular types of food allergies, Gern said.
“The authors may be over-interpreting the relationship between pets and specific food allergies like milk or wheat,” Gern said. “They performed numerous comparisons, increasing the possibility that some random associations will be deemed significant.
“I would also not put much stock in the hamster data,” he added. “There were not many hamster owners and they only saw one association, with nut allergies.”
Overall, however, the findings on the benefits of living with pets fits well with many previous studies, he said.
“The benefits of exposure to animals have been demonstrated in several different contexts,” Gern said in an email, “such as with pets (like this study), farm animals (Central Europe, Amish, and Wisconsin dairy farms), and even pests (mice and cockroaches) in disadvantaged inner city homes. Perhaps the overall message is that a biodiverse environment promotes immune development and healthy children.”