Study finds childhood exposure to cats and dogs reduces risk of allergies
In the past, doctors might have told parents of young children at risk for allergies and asthma to find a new home for Fido or Fluffy. Now they may have reason to pause. Research published in the August 28, 2002 Journal of the American Medical Association found that children who were exposed to two or more cats or dogs in the first year of life had a reduced risk of developing sensitivities to multiple allergens, and possibly asthma.
The results of this study surprised even the researchers, since household pets have long been assumed to be culprits in childhood allergies. Studies looking back in time had identified a link between allergies and early exposure to cats and dogs. Other research, however, showed that children who grew up on farms with animals were less likely to be allergic than children who didn’t grow up around farm animals.
About the study
Researchers at the Medical College of Georgia and Wayne State University in Detroit, Michigan studied 474 Detroit-area children from birth to an age of 6 to 7 years, who participated in the Childhood Allergy Study. Previously, the authors examined the influence of maternal smoking on allergies in these children, and this same data was reanalyzed to look at the role pets may play in developing allergies. The original study included 835 children who underwent testing of their umbilical cord blood for immunoglobin E (IgE) concentration. IgE is a type of antibody (protein produced by the immune system) that is specific for one particular allergy-producing substance. While an initial exposure to a specific allergen does not generally produce allergic systems, when an allergen encounters its specific IgE antibody it attached to the antibody like a key fitting into a lock. This then leads to release of chemicals like histamine, which causes the symptoms of allergies.
The original study collected information on parental allergy histories, parental smoking, IgE levels in cord blood, month of birth, concentration of dust mite and cat allergens in the child’s bedroom at age two years, and pet exposure. Pet exposure was determined at one year of age by asking parents about the presence and number of pets in the home. When the children were six to seven years old, skin prick and blood tests for allergens were performed and parents were asked if a doctor had diagnosed the child as having asthma.
The researchers compared the allergy tests and asthma results of the 184 children who had been exposed to two or more cats or dogs in their first year of life with the 220 children who had not been exposed.
Study results indicated that exposure to two or more cats or dogs in the first year of life was beneficial in reducing the risk of allergies among these children. For example, researchers found that 8.6% of the children not exposed to a dog had a positive skin test result to dog allergen, while only 3.3% of children exposed to dogs during their first year of life showed a positive reaction.
This effect was apparent even after the researchers accounted for other allergic risk factors and variables associated with pet ownership. Specifically, adjustments were made for cord blood IgE concentration, sex, older siblings, parental smoking, parental asthma, bedroom dust mite allergen levels at two years, and current cat and dog ownership.
Although these results suggest that exposure to pets in the first year of life could reduce allergies and asthma in children, there are a number of limitations to the study. First, children in this study were all non-Hispanic whites from relatively educated families. Since asthma disproportionately affects low-income, minority groups these results may not be applicable to the population most at risk for asthma. The effects of the “Detroit” environment are also unknown and highlighted by the fact that researchers in Arizona conducted a similar study and saw no effect of animal ownership. The sample size and the number of children who did not complete the study (361) are also limitations, though children who did not complete the study were not significantly different from the children who did. With a larger number of study subjects, the researchers could further explore any differences between boys and girls exposed to just dogs, just cats, or both. The researchers also did not consider possible exposure to dogs and cats outside of the home, which could have had an influence on the observed results.
How does this affect you?
So, does this mean you should buy a pet to protect your children from allergies and asthma? It’s unlikely your family physician will start writing a prescription for a pet anytime soon, but this study suggests that families that already have pets or were thinking of getting one need not worry about allergies and asthma. Pregnant women should be careful to have someone else change and clean the cat’s litter box, however, because of the possibility of being exposed to a rare, but potentially serious disease called toxoplasmosis. When in doubt, consult your physician.
Asthma and Allergy Foundation of America
Ownby DR, Johnson CC, Peterson EL. Exposure to dogs and cats in the first year of life and risk of allergic sensitization at 6 to 7 years of age. JAMA. 2002;288:963-972.
Platts-Mills TAE. Paradoxical effect of domestic animals on asthma and allergic sensitization. JAMA. 2002;288:1012-1014.
Last reviewed Aug 30, 2002 by Richard Glickman-Simon, MD
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