Cats associated with reduced odds for childhood asthma
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Key takeaways:
- Risks fell with ownership in both early life and at school age.
- There were no associations when children had cats only in early life or at school age.
- There were no associations between asthma and dog ownership.
Children in Puerto Rico who grew up with a cat in their household were 68% less likely to develop asthma, according to a study published in Annals of Allergy, Asthma & Immunology.
However, there were no associations between dogs and asthma, Yueh-Ying Han, PhD, MS, research associate professor of pediatrics, division of pulmonary medicine, department of pediatrics, UPMC Children’s Hospital of Pittsburgh, University of Pittsburgh, and colleagues wrote.
“Although pet ownership has been associated with allergic diseases such as asthma, the evidence is inconsistent, partly due to variability in time of exposure, outcome assessment, or adjustment for environment factors. Moreover, there are limited longitudinal studies, particularly in minoritized youth,” Han told Healio.
“Of note, this is the first known prospective study of cat exposure and asthma or allergic sensitization in Puerto Ricans,” she added.
Data came from the PROspective study of Puerto Rican youth and Asthma, or PROPRA, including 173 children who did not have asthma (mean age, 9.9 years) and 211 with asthma (mean age, 10 years).
In addition to a greater statistically significance probability for male sex (58.3% vs. 46.8%; P < .05), the group with vs. without asthma also was significantly more likely to have mold or mildew in their house in the previous year, a family history of atopy, one or more positive allergen-specific IgE tests, an unhealthy diet and a higher BMI z score (P < .05 for all).
Along with administering questionnaires to the children’s caregivers, researchers conducted a baseline visit with each child at age 6 to 14 years and then a follow-up visit at age 9 to 20 years. Children were stratified into four groups:
- never owned a cat (reference group);
- ownership in early life (during pregnancy or during the first year of life) but not at either study visit (school age);
- ownership during at least one study visit but not in early life; and
- ownership in early life and at least one study visit (persistent ownership).
Compared with the reference group, odds for asthma were 68% lower for children with persistent ownership (OR = 0.62; 95% CI, 0.11-0.92).
“However, persistent exposure to a cat was not associated with sensitization to any of five common allergens (house dust mite, cockroach, cat dander, dog dander and mouse urinary protein) or sensitization to cat allergen specifically,” Han said.
Also, a multivariable analysis did not find any significant associations between asthma and ownership of a cat early in life only or ownership at school age only, nor was there any significant association between dog ownership at any age and asthma.
“The inverse association between persistent cat ownership and asthma in Puerto Rican youth was independent of other covariates that may affect asthma risk, including socioeconomic status, body mass index, family history of atopic diseases, exposure to second-hand smoke and dietary habits,” Han said. “Further, our findings were unchanged after excluding participants whose family had given away pets after the child was born.”
A comparison of the 23 children with persistent ownership of a cat with the 275 who never owned a cat found that caregivers of children with persistent ownership were more likely to give away a pet due to asthma and have higher levels of Fel d 1 in their household dust than the caregivers of children with no cat ownership. There were no other significant differences between the groups based on other characteristics.
There was a significant association between dog ownership at school age only and with a positive IgE result for dog allergen, the researchers said, but there were no significant associations between any of the categories of dog ownership and positive IgE results to one or more allergens.
Compared with the full cohort, associations between cat ownership and asthma were similar among the 294 children whose families never gave away any animals (adjusted OR = 0.21; 95% CI, 0.06-0.81).
Based on these findings, the researchers concluded that there was an association between persistent ownership of a cat and lower odds for asthma at school age, although links between persistent ownership and sensitization to cat allergen or to one or more allergens could not explain this association.
“Despite some study limitations, our results suggest that cat ownership during childhood is not detrimental and may be beneficial in Puerto Rican households without members who are already allergic to a cat,” Han said.
However, the researchers called for additional studies with larger sample sizes to evaluate if and how risks for asthma among this and other marginalized populations may be mitigated by long-term exposure to high levels of cat allergen.
“The mechanisms explaining how persistent exposure to cat allergen is linked to reduced risk of asthma deserve further examination,” Han said.
“Larger longitudinal studies should evaluate long-term exposure to high level cat allergen from pregnancy to school age and asthma development over time,” she continued, “particularly in minoritized high-risk groups such as Puerto Rican youth.
For more information:
Yueh-Ying Han, PhD, MS, can be reached at hany2@upmc.edu.
Perspective
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This is the first time that researchers have studied persistent cat or dog ownership and how that is associated with asthma. This study found a difference between having a cat or dog at one point in childhood vs. having a pet throughout childhood.
Even after adjustments for other variables, patients still had a 68% reduction in the odds for developing asthma if they had a cat starting at birth or before age 2 years, and then continuing throughout childhood.
We may need to rethink concerns about children with cats and dogs in the home.
Perspective
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The findings are not necessarily surprising — often referred to as the hygiene hypothesis — given the physiological basis of how early exposure to pets during infancy such as living on a farm impacts immune response development in favor of Th1 and decreases chances for later development of asthma, including reducing Th2 response, which is the allergic pathway that is associated with asthma.
However, this is the first prospective longitudinal evaluation of the association between pet exposure (both early and continued) on asthma in children. Although limited to only children in Puerto Rico, with a relatively small sample size, the strength (68% reduction) of the inverse relationship between cat exposure and asthma is interesting and could have clinical implications with further study in a more diverse sample.
I do not believe I have a particular case for which these findings are true, but I also do not see many patients with cats as pets. Generally, however, the presence of multiple confounders such as pollution, pests and mold makes it difficult to ascertain the impact of pet exposure on children I see in clinic.
We do not know who will and won’t develop asthma when children are born. However, children born to families with high risk for predictive index for asthma (atopic disease in parents or siblings) who are considering having a cat as a pet could consider exposing the infant to cats during the first year of life instead of waiting for them to be aged older than 2 years.
Early pet exposure, before the first year of life, also could be something to consider for families with familial atopy when considering the risk for asthma in their children. Mostly, little harm could come of this, and perhaps there could even be a benefit, as opposed to getting a pet after the child is school age, which, based on prior retrospective studies, could be more troublesome for their child’s asthma.
As this was limited to children in Puerto Rico, it would be helpful to study this (early and continued pet exposure and association with asthma outcomes) prospectively in a cohort of children in different countries. The researchers also found that children who were excluded for other reasons were more likely to live in an apartment, for example, so housing type could have an impact on this association. Additionally, a larger study may allow for a more robust analysis of the only early life and only at school age exposure groups.
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