Scientists explore weighty data linking asthma and acetaminophen

In 1998 Dr. Arthur Varner, a fellow at the University of Wisconsin Medical School, published his suggestion that perhaps the dramatic rise in asthma occurring during the past thirty years was associated with the radical change from aspirin to acetaminophen as the treatment of choice for childhood fevers.  Since then, 20 different studies have been published suggesting a link between acetaminophen and asthma.  Unfortunately, most have been confounded by the fact that the subject children are likely to be receiving acetaminophen to address viral illnesses that have also been linked to asthma:  it has not been clear whether scientists are simply tracing the association between a treatment for infectious fever and an infectious cause of asthma.

One study intended to address this potential confounding of causation randomly assigned young patients to receive either ibuprofen or acetaminophen for fevers.  The acetaminophen patients did report significantly more asthma symptoms in the following year. A larger study is now being undertaken in an attempt to further quantify this relationship and scientists note that both acetaminophen and non-steroidal anti-inflammatories each have risks and advantages.  Nevertheless, one physician was quoted in the New York Times to the effect that he would prescribe his child ibuprofen for fever, given the present state of knowledge.

The existing studies do make a circumstantial case for Varner's hypothesis.  They demonstrate, for example, that even a single dose of acetaminophen can reduce the body's levels of glutathione, an enzyme that helps repair oxidative damage that can drive inflammation in the airways.  Several studies document a dose-response relationship between acetaminophen and asthma accross age, geography and culture.  There is a documented risk for children whose mothers took acetaminophen during pregnancy.  One study involving 31 different countries showed that children who were adminsistered acetaminophen in the first year of life were fifty percent more likely to demonstrate asthma symptoms (although they were probably taking the drug because the had an higher underlying proportion of viral illnesses when compared as a group to the control population that never needed/took acetaminophen).  Children who took acetaminophen at least once a month were three times as likely to develop asthma.  Further, the prevalence of asthma in 36 different countries in the year 2000 directy correlated with the increase in acetaminophen sales in those countries.  Children's risk of wheezing was double compared with kids who never needed to take, and had not taken acetaminophen.