Antibiotic use in early life may increase the risk of asthma in children, a review conducted by researchers at the Yale School of Public Health has found.
The study estimated that children exposed to antibiotics in their first year of life had a 16 percent greater likelihood of developing asthma by the age of 18, while those exposed during gestation—via antibiotics prescribed to their mothers—had a 24 percent greater likelihood. However, the authors caution that these conclusions are not definitive, as many studies included in the review were susceptible to several possible sources of bias.
The study in the journal Pediatrics was a systematic review and meta-analysis of previously published research that has investigated the connection between antibiotic use and childhood asthma, and included 22 publications in its analysis.
The role of antibiotics in the development of asthma has received significant attention in recent years due to the so-called “hygiene hypothesis,” which theorizes that children who grow up in overly hygienic environments have a low exposure to bacteria and a resulting increased risk of asthma. This could explain why asthma is much more common in industrialized countries than non-industrialized countries. Abnormally low levels of bacteria in the gut during the first few years of life, which can be caused by the use of broad-spectrum antibiotics, is thought to cause permanent imbalances in the immune system, leading to the development of allergic diseases including asthma.
“Even if the increased risk of asthma after using antibiotics is small, the fact that the prevalence of antibiotic use is so high means that a large number of children will develop asthma as a result of this exposure. These findings place added emphasis on the need to reduce unnecessary antibiotic prescriptions during pregnancy and early life,” said Michael B. Bracken, Ph.D., who led the study.
The authors sought to minimize bias in their analysis by focusing on studies that controlled for a phenomenon known as “reverse causality,” which is an artificial association between an exposure and a disease that occurs when a disease is causative of an exposure, rather than the other way around.
Studies of the connection between antibiotics and asthma are particularly sensitive to this type of bias, since antibiotics may be given to treat early symptoms of unrecognized asthma, which can be mistaken for the symptoms of respiratory infections.
However, the Yale group found that, even among studies that attempted to control for reverse causality, there was still a significant association between antibiotics and asthma. This conclusion was also supported by their analysis of studies that examined gestational exposure to antibiotics, which avoids the problem of reverse causality, since the antibiotics are prescribed for maternal infections.
Despite their findings, the authors said that additional well-designed studies are needed before a definitive conclusion can be made about the connection between antibiotics and asthma, since it was not possible to completely rule out the effect of reverse causality and other possible biases in many of the published studies.
Antibiotics are routinely given to infants to treat respiratory diseases, even though most of these diseases are viral infections that do not respond to antibiotics. Approximately one-third of all infants in the United States receive antibiotic prescriptions, and a similar proportion of mothers receive antibiotics during pregnancy.
Bracken is the Susan Dwight Bliss Professor of Epidemiology at the Yale Center for Perinatal, Pediatric, and Environmental Epidemiology (CPPEE). Other investigators were William Murk, a recent graduate from the Yale School of Public Health and lead author of the study, and Kari Risnes, M.D., a pediatrician from the Norwegian University of Science and Technology and a visiting scholar atthe CPPEE.