Babies exposed to dogs may have lower risk of asthma, study finds

Babies who grow up in dog-owning families could end up with an unexpected advantage by the time they reach preschool. Early exposure to dog allergens has been shown to be linked with lower asthma risk and better lung function at five years of age, new research has shown. The findings, presented at the European Respiratory Society Congress in Amsterdam, give a glimpse of how pet household members can influence child health.

Asthma remains one of the most common chronic diseases in children, typically developing in the early years of life. It can be triggered by both genetic factors and environmental factors like air pollution, infections, and allergens.

Dr. Jacob McCoy of The Hospital for Sick Children in Toronto described how kids spend a lot of their time indoors, so household allergens are a key part of the equation. "Asthma is a very frequent chronic respiratory condition in children, with the most prevalent rates in the initial four years of life," he said. "They are key risk factors that we might be able to modify and decrease asthma.

To dig deeper, researchers turned to the Canadian CHILD cohort study, which has followed families nationwide for years. The scientists studied 1,050 children, taking into account dust samples taken from their homes when they were a few months old. They measured three potential allergens: Can f1, a protein that sheds from dog skin and saliva; Fel d1, the same protein in cats; and endotoxin, a molecule found on some bacteria.

The children's lung capacity was measured by doctors at age five, looking at how much air they could exhale in one second after filling their lungs. Blood was also taken to identify genetic markers for asthma and allergy risk factors. The findings were astounding.

Babies who were exposed to higher levels of dog allergen had nearly a 48 percent lower chance of developing asthma at age five. Not only that, but they also showed increased lung function compared to peers with lower exposures. This protective effect appeared to be even greater in children who were already genetically predisposed toward greater risk of breathing distress.

In contrast, neither exposure to cat allergen nor exposure to bacterial endotoxin showed any suggestion of protection. "We discovered that, although cat allergens were not found to have an association, exposure to dog allergens was associated with better lung function and fewer asthma risks," explained Dr. McCoy.

How this occurs is not yet entirely understood, but scientists believe it may have something to do with alterations in the nasal microbiome or an impact on the immune system. "Pre-exposure to dog allergens early in life may avoid sensitization, possibly by altering the nasal microbiome – the community of microbes that reside in the nose – or through some impact on the immune system," he continued.

The results give new significance to the decades-long argument concerning pets and the health of children. While previous studies have yielded conflicting results, this study stands apart due to the large population sample and in-depth exploration of allergens in the household. But the scientists are quick to point out that more studies have to be carried out before any definitive conclusions can be drawn.

Dr. Erol Gaillard, chair of the European Respiratory Society's expert panel on child asthma and allergy, finds the results encouraging but not definitive.

"Asthma is the most common chronic illness of childhood and youth and also one of the main reasons for children being admitted to hospital for emergency treatment," joined Gaillard, an associate professor at Leicester University not involved in the study. "This study suggests that babies exposed to dogs throughout their lives have a decreased risk of developing asthma."

This may be reassuring for pet dog-owning households; but we need to learn more about this connection and what it implies for children's developing lungs in the long term.

For parents, the findings lay to rest concerns about having a dog in the home when they bring a baby into the world. But the scientists caution that protection only existed when exposure was early and not among children who became sensitized to dog allergens later in childhood. In those youngsters, exposure worsens asthma.

The study authors expect the work to be followed by further research on how allergens, microbes, and the immune system interact early in life.

The study has suggested a potential approach to reducing the risk of asthma by simply having a dog at home in early life. It can change the outlook of families towards pet ownership during pregnancy and infancy if other research sustains it. It also goes to highlight the importance of the indoor environment in shaping health outcomes.

Understanding how dog allergens impact immune development can yield novel methods to avert asthma, one of the leading reasons children are treated in emergency departments.

Physicians even may, in the future, leverage this knowledge to devise treatments that mimic the protective effect of early exposure to allergens without families needing to have dogs.

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