Growing up with cats, dogs can reduce risk for allergies, study says

DVM Magazine Oct, 2002

Detroit- Children who grow up with pets may be less likely to develop allergies later in life, a new study reports.

Contrary to widespread belief, children who grow up with cats or dogs may be at less risk for developing pet allergies and less susceptible to ragweed, grass and dust mite allergies, according to a Henry Ford Hospital study published in the the Journal of the American Medical Association.

The study, funded by the National Institutes of Health, is believed to be the first of its kind in the United States that showed early exposure to pets has a protective effect on developing pediatric allergies.

The 10-year study showed that children exposed to two or more cats or dogs during the first year of life were half as likely to develop common allergies at ages 6 or 7 than those not exposed to pets.

Children exposed early to pets had overall lower antibody levels and fewer positive skin test reactions to dog, cat, ragweed, grass and dust mite allergens.

"Traditionally, allergists recommend that expectant parents who have a history of allergies and want to reduce the risk for their children not have a pet in the household,"says Christine Cole Johnson, PhD., co-principal investigator and senior research epidemiologist for Henry Ford Hospital.

"This study indicates that having a pet around when a child is very young may influence the development of a child's immune system. While more research is needed, if an expectant parent with a history of allergies came up to me and wondered whether their cats or dogs had to go, I would tell them to keep the pets:"

Johnson says researchers theorize that exposure to cats and dogs may influence the development of a child's immune system through exposure to endotoxins, bacterial products commonly associated with the presence of pets.

"For reasons that are not yet completely understood, endotoxins are thought to cause the immune system to respond differently and protect against common allergies;' she says.

For the study, researchers followed 474 children born between 1987-1989 who at birth were members of Health Alliance Plan, a Detroit-based health insurer. Of the study group, 242 were girls; 232 were boys.

Data was collected prenatally, at birth and at regular intervals until the children were 6 and 7 years old. The study included blood tests that measure antibodies (immunoglobulin E) that
cause allergies; skin reaction tests that show whether a person is hypersensitive to an allergen; and a pulmonary test that estimates the reactivity of the airways. Reseachers also collected data on exposure to cigarette smoke, home and day care environments, and measured allergen levels in household dust and air samples.

Nearly 31 percent of the children studied lived with dogs as infants; 14 percent lived with cats; and 8 percent of the children lived with both More than half of the children's parents had a history of allergies or asthma.

According to the study, by age 7, children who had lived with two or more cats or dogs during the first year of life were less likely to have one or more positive skin reaction tests to a battery of indoor and outdoor allergens compared to those who were not exposed to pets (15 percent vs. 34 percent).

By age 7, children who had lived with two or more cats during the first year of life were less likely to have a positive skin reaction test to cat allergen compared to those who were not exposed to cats (8 percent vs. 16 percent).

By age 7, children who had lived with two or more dogs during the first year of life were less likely to have a positive skin reaction test to dog allergen compared to those who were not exposed to dogs (3 percent vs. 9 percent).

By age 7, children who had lived with two or more cats or dogs during the first year of life
were less likely to have a positive test for the antibody to outdoor allergens like ragweed, grass and mold compared to those who were not exposed to pets (12 percent vs. 30 percent).