March 13, 2006 -- Babies treated with even one course of antibiotics during their first year of life may have twice the risk of developing asthma later in childhood as unexposed babies, an analysis of past research shows.
The findings bolster the theory that an increase in the use of antibiotics early in life may be a factor in the epidemic rise in childhood asthma. They also suggest that greater exposure to antibiotics is associated with greater asthma risk.
Approximately one in eight children in the U.S. has asthma, and asthma rates among children under age 5 have increased especially between 1980 and the mid-1990s, according to figures from the CDC.
While results from the pooled studies point to a link between early antibiotic exposure and asthma, they fall short of proving the association, says Carlo A. Marra, PhD, PharmD, of the University of British Columbia.
"Antibiotic exposure during the first year of life does appear to be a risk factor for the development of childhood asthma, but because of limitations in the studies we reviewed we have to conclude that bigger and better studies are still needed," he tells WebMD.
Different Studies, Different Findings
The association between early antibiotic use and childhood asthma was significantly stronger in studies that relied on parent recall than in those that followed children over time.
Marra says the recall, or retrospective, studies may have been compromised by bias. Specifically, the parents of the children with asthma may have been more likely to report early antibiotic exposures than parents of children without asthma.
An analysis of five studies that examined the effect of treating infants with multiple courses of antibiotics showed that greater exposure to the drugs was associated with greater asthma risk. But this association was again seen in the retrospective studies.
The study is published in the March issue of the journal Chest.
While not conclusive, Marra says the findings offer some of the strongest supporting evidence yet in favor of the so-called 'hygiene hypothesis,' which suggests that increasingly sterile environments may be making children more susceptible to allergies and asthma.
Early use of antibiotics has been implicated because the drugs kill good bacteria in the gut, which may, in turn, weaken the immune system.
Allergist Clifford W. Bassett, MD, FAAAAI, says the analysis illustrates the potential importance of early environmental exposures in future health.
He adds that it is up to pediatricians and other doctors who treat babies and children to educate parents about when antibiotics are beneficial and when they are not.
Bassett is with The Long Island College Hospital in Brooklyn, N.Y. He is also vice chairman of the public education committee of the American Academy of Allergy, Asthma, and Immunology.
"Clearly, you wouldn't want to withhold an antibiotic when it is needed because of a theoretical risk of asthma," he says. "But this research does underscore the importance of not overusing these drugs, especially early in life."