The Asthma – Tylenol Link

I have been seeing a number of articles in the news recently reporting a theory that acetaminophen (Tylenol) use in children is linked to the development of asthma.  Proponents of the theory site several lines of evidence.  One is the observation that about 30 years ago parents began to give children with fever acetaminophen in place of Aspirin because of a link between Reye’s syndrome and Aspirin.  This occurred about the same time  that researches began to document a significant increase in asthma cases.  Also, studies have shown that parents of children with a diagnosis of asthma report given their children acetaminophen more frequently.

There are problems with using these observations to conclude that acetaminophen use causes asthma.  Most importantly is the fact that viral respiratory infections, like the rhinovirus that causes the common cold,  are by far the most important triggers of wheezing episodes in children. Many children with wheezing episodes associated with colds go on to develop true asthma but many do not.  In addition, researchers have suggested that certain viral respiratory infections such as the respiratory syncytial virus (RSV) may produce a type of airway injury that leads to the development of asthma.   Since children that have more frequent colds and associated conditions such as ear and sinus infections would be given acetaminophen more often for pain and fever, it is difficult to determine the true link.  In other words, is the observed increase in asthma the result of acetaminophen use or a change in the frequency and types of infections (as well as, perhaps, expectations of parents) that the acetaminophen is used to treat?   Other considerations include the use of antibiotics and vaccinations, declining family size, urbanisation, and pasteurization: all dramatically changed in the past thirty years.

One point is clear however: Reporting a link between Tylenol use and asthma will attract more readers than noting that sick children are more likely to have symptoms.