By Dr. Karen Shaw Becker
One of the many benefits of pet ownership seems to be improved health in babies and children who live with furry family members, and now new research has revealed that young children with a cat at home have a reduced risk for asthma. The study, conducted in Denmark, involved 377 toddlers born to asthmatic mothers, and was published in the Journal of Allergy and Clinical Immunology.1
Genetic Variant Responsible for Many Cases of Childhood Asthma
There have been many studies in recent years to evaluate the effect of exposure to cats and dogs early in life on the incidence of childhood asthma. These studies have frequently contradicted each other. Some researchers believe exposure is a risk factor, while others conclude it has a protective effect.
These conflicting outcomes point to the likelihood that a genetic component in some cat-owning children triggers a protective effect against asthma. Genetic variation at the chromosome 17q21 locus is the strongest known genetic risk factor for childhood asthma, and kids with this genotype often develop the disease and suffer with frequent episodes and acute severe attacks.2
Almost 1 in 3 children in the Denmark study carries the genetic variant, which is thought to be proportionate to the population in general. When the variant is activated, it doubles the risk the child will develop asthma before age 12 and also plays a role in bronchitis and pneumonia.
Study Results Show Exposure to Cats Decreases Asthma Risk in Genetically Predisposed Kids
Per the American Academy of Allergy Asthma & Immunology, which reported on the study:
"Cat exposure attenuated the risk of asthma development during the first 12 years of life in children with the high-risk genotype, but had no effect in children with the low-risk genotype. Increasing levels of cat allergens collected in the children's homes were associated with increased protection from asthma in these high-risk children.
The researchers found no such effects of exposure to dog. The high-risk asthma 17q21 genotype was also associated with a higher risk of pneumonia and bronchiolitis, and this risk was likewise decreased in children exposed to cat. Replication studies showed similar results on asthma risk."3
Lead researcher Dr. Jakob Stokholm believes the explanation for the protective effect of exposure to cats may be related to bacteria the animals carry, as well as fungi or viruses they bring into the home.
"It's very exciting that they find this connection because other studies have struggled to conclude anything final," said Dr. Arne Høst, study co-author. "Now it looks like the effect is linked to a particular gene-variant, which goes to show just how complex the development of asthma and allergies are. It's not only about genes and the environment, but how the two interact, and there's so much that we still don't know."4
Additional Child Health Studies Involving Cats
A 2011 study followed over 550 kids from birth to age 18, and regularly gathered data from the children's families about the presence of indoor pets.5 At the end of the study, blood samples were taken to test the study participants for allergies to cats and dogs.
The kids who had a cat at home during their first year of life were 50 percent less likely to be allergic to cats than the children not exposed from birth to 1 year. Researchers concluded exposure to pets at later ages didn't make much of a difference. It was exposure during infancy that was important, leading study authors to conclude, "The first year of life is the critical period during childhood when indoor exposure to dogs or cats influences sensitization to these animals."
In a 2005 study of children with respiratory symptoms living in Italy, researchers looked at the link between early cat ownership and development of allergic rhinitis.6 They concluded early cat ownership significantly lowered the risk of developing allergies to cats. Early exposure to kitties was also linked with a significantly lower risk of allergic rhinitis than cat ownership later in life, or no cat ownership. The study authors concluded that:
"Cat ownership in early childhood can play an important role in preventing sensitization to cat and in lowering the frequency of allergic rhinitis, at least in children with the characteristics of the population studied."
Studies of Dog and Dog-and-Cat Ownership and Childhood Health
In a 2009 study, pet ownership between birth and age 9, and between 18 and 32 was investigated.7 Allergy (skin prick) tests were performed on study participants at 13 and 32 years of age. Results suggested children who lived with both a cat and a dog were less likely to have allergies at 13. However, living with just a cat or a dog did not provide the same benefit. For the kids who were not allergic by age 13, having both a dog and cat in adulthood resulted in lower risk of new allergies by age 32.
The objective of a study published in 2008 was to determine if the effects of exposure to pets on immune development and allergies in young children could be explained by changes in exposure to innate immune stimuli in settled dust.8 The study authors' concluded that:
"Exposure to dogs in infancy, and especially around the time of birth, is associated with changes in immune development and reductions in wheezing and atopy [allergic hypersensitivity]."
Another 2008 study published in the journal of the European Respiratory Society investigated the link between contact with dogs and exposure to endotoxins during infancy, and the development of allergies up to 6 years of age.9 Researchers concluded children exposed to a dog in the home during early childhood had a significantly lower rate of mixed pollen and inhalant sensitivity from birth to 6. Interestingly, this study did not find that these children had less sensitivity to dogs despite early exposure.
Kids who had regular contact with dogs, but who did not actually live with one, did not have reduced rates of pollen and inhalant sensitivity similar to the children who lived with dogs in the home. Study results did not link house dust endotoxin exposure during infancy and development of allergies. The researchers concluded living with a dog during early childhood protects against inhalant allergies.
A study published in 2002 evaluated the link between dog and cat exposure in the first year of life and allergic sensitization at the age of 6 to 7.10 Researchers concluded children exposed to two or more dogs or cats during their first year were less likely to develop allergies to not only dog and cat hair, but also dust mites and ragweed.
Allergies and the Hygiene Hypothesis
The theory of the hygiene hypothesis, born in the late 1980s, is that the huge increase in allergic disorders in the last century is due in part to our somewhat obsessive cleanliness standards. Since the advent of antibacterial products for every conceivable use, we've become hypervigilant in trying to avoid every germ in the environment. On the surface this might seem like a sensible approach, but not everyone is convinced.
It is thought that early exposure to bacteria and parasites prepares immature immune systems to fight dangerous infections. Further, this priming" of the immune system also helps it learn the difference between serious health hazards like a pneumonia infection, and harmless irritants like pet dander and pollen.
According to the hygiene hypothesis, when the immune system remains naïve from lack of exposure to real pathogens, it is more likely to mount attacks against benign environmental triggers. It's possible then, that exposure to pets in the home during the first years of life helps a child's immune system become balanced in terms of recognizing the difference between harmless and potentially pathogenic organisms.