But it raises important safety concerns about the most commonly used drug in the U.S.: the fever-reducing painkiller acetaminophen (also known as paracetamol), the main ingredient in Tylenol.
People should think twice about using acetaminophen, but nobody should stop taking it or giving it to children with high fevers, says study leader Richard Beasley, DSc, a professor at the Medical Research Institute of New Zealand.
"[Acetaminophen] use might be a risk factor for the development of asthma in childhood. This issue urgently requires randomized controlled trials," Beasley tells WebMD in an email interview. "In the meantime, [acetaminophen] remains the preferred drug for relief of pain and fever in childhood, and for use by both children and adults with asthma."
Beasley recommends that parents give children acetaminophen only when they have a fever of more than 101 degrees Fahrenheit.
The study shows:
- A 46% increased risk of asthma at ages 6-7 years in kids who got acetaminophen for fever in their first year of life.
- A 48% increased risk of runny nose and red, itchy eyes at ages 6-7 in kids who got acetaminophen for fever in their first year of life.
- A 35% increased risk of eczema at ages 6-7 in kids who got acetaminophen for fever in their first year of life.
- A threefold higher risk of current asthma symptoms in 6- to 7-year-olds who took acetaminophen at least once a month compared with those who did not take the drug.
- 22% of severe childhood asthma is linked to acetaminophen use during the first year of life.
- 38% of severe childhood asthma is linked to acetaminophen use later in childhood.
Does Acetaminophen Cause Asthma?
The Beasley study, in which parents are asked to recall their use of acetaminophen after the fact, cannot prove acetaminophen causes asthma.
However, Beasley and colleagues note that there are several reasons to suspect this is so:
- The link between acetaminophen and asthma is strong.
- The more acetaminophen a child uses, the higher that child's risk of severe asthma.
- Acetaminophen is linked to asthma in many different cultures with different medical practices.
- Acetaminophen use came before asthma symptoms appeared.
- Asthma prevalence shot up in the same years acetaminophen use became widespread.
In an editorial accompanying the study, Columbia University researcher R. Graham Barr, MD, DrPH, agrees with Beasley that while the study does not prove acetaminophen causes asthma, a clinical study is urgently needed.
"This is a major public health concern," Barr tells WebMD. "Given the widespread use of acetaminophen and ibuprofen among kids -- and asthma being the disease of greatest burden in kids -- this would seem to be an important topic for further study."
Barr notes that previous studies have linked acetaminophen, but not ibuprofen, to asthma and have linked use of acetaminophen during pregnancy to childhood asthma.
Barr's own research team previously found that high-level acetaminophen use raised women's risk of adult-onset asthma.
"There is still a lot of uncertainty about this," he says. "There might be something going on, but do we have a clear public health recommendation at this time? I don't think we do."
Childhood Lung Problems Increase Adult Asthma
Underscoring the importance of early-childhood events for later asthma is a study from the University of Arizona, Tucson.
Fernando D. Martinez, MD, director of the Arizona Respiratory Center at the University of Arizona, and colleagues followed 849 children from birth to age 22.
Those with adult asthma were:
- 7.4 times more likely to have had childhood asthma
- 14 times more likely to have had persistent wheezing as children
- 3.6 times more likely to have had a childhood mold allergy
- Twice as likely to have had low airway function at age 6
More than 70% of the adults who had adult asthma were women.
"We conclude that asthma that apparently develops early in adult life affects mainly women and is commonly the clinical expression of latent changes of airway responses that are present in the preschool years," the researchers conclude.
The Beasley and Martinez studies, and Barr's editorial, appear in the Sept. 20 issue of The Lancet.