Children who receive antibiotics within the first six months of life are at a significantly increased risk of developing asthma and allergy by 6 years of age, new research by the Yale School of Public Health suggests.
The study followed a large cohort of women and collected data throughout their pregnancies and from their children until their sixth birthday. The researchers found that infants exposed to antibiotics during their first six months of life were up to 52 percent more likely than their peers who did not receive antibiotics to develop childhood asthma and allergies.
While previous studies have also found that antibiotic use may increase the risk of asthma in children, those studies may have been biased because antibiotics are used to treat respiratory tract infections that could themselves be early symptoms of asthma. The Yale study sought to eliminate this bias and concluded that antibiotic use increased risk of childhood asthma even in children not having experienced respiratory tract infections and in children whose asthma is first diagnosed after 3 years of age.
Another controversy from earlier studies has been whether the effect of antibiotic use is different in children who are genetically pre-disposed to asthma. The Yale research was designed to study this since 40 percent of participating mothers had asthma. The findings suggest that the adverse effects of antibiotic use on asthma risk were much stronger in children who did not have any asthmatic parents. The conclusions are reported online in the American Journal of Epidemiology.
The research was done by the Yale Center for Perinatal, Pediatric and Environmental Epidemiology (CPPEE), and led by Michael B. Bracken, the Susan Dwight Bliss Professor of Epidemiology.
Antibiotic use and increased asthma and allergy risk relates to the so-called “hygiene hypothesis,” which may explain why asthma rates have increased in developed countries by children growing up in an apparently overly hygienic environments, Bracken said. Very early microbial exposure, particularly in the intestinal tract, seems necessary for transition to a mature and balanced immune system in childhood. Antibiotic use, especially broad spectrum antibiotics, may alter microbial flora in the gut, thereby causing imbalances in the immune system and a poor allergic response.
A third of U.S. infants are exposed to antibiotics in the first six months of life, most commonly for respiratory tract infections, although the majority of these diseases are viral and do not respond to antibiotics. The use of broad spectrum antibiotics continues to increase.
“The findings from our study should encourage physicians to avoid unnecessary antibiotic use, especially in low-risk children,” said Kari Risnes, a pediatrician from the Norwegian University of Science and Technology, visiting researcher at CPPEE and the study’s lead author. The other investigators were Kathleen Belanger, Ph.D., a research scientist at Yale, and William Murk, a recent YSPH graduate.