Exploring asthma’s trigger in children

Since then,more than 20 studies have produced results in support of his theory,including a large analysis of data on more than 2,00,000 children that found an increased risk of asthma among children who had taken paracetamol. In November,Dr John T McBride,a pediatrician at Akron Children’s Hospital in Ohio,published a paper in the journal Pediatrics arguing that the evidence for a link between paracetamol and asthma is now strong enough for doctors to recommend that infants and children who have asthma (or are at risk for the disease) avoid paracetamol.

Dr McBride based his assertion on several lines of evidence. In addition to the timing of the asthma epidemic,he said,there is now a plausible explanation for how acetaminophen might provoke or worsen asthma,a chronic inflammatory condition of the lungs. Even a single dose of acetaminophen can reduce the body’s levels of glutathione,a peptide that helps repair oxidative damage that can drive inflammation in the airways,researchers have found.

“Almost every study that’s looked for it has found a dose-response relationship between paracetamol use and asthma,” Dr McBride said. “The association is incredibly consistent across age,geography and culture.”

A statistical link between acetaminophen and asthma has turned up in studies of infants,children and adults. Studies have also found an increased risk of asthma in children whose mothers who took acetaminophen during pregnancy.

For instance,a study published in The Lancet in 2008 examined information collected on more than 2,05,000 children from 31 countries as part of the International Study of Asthma and Allergies in Childhood,known as the Isaac study. The 2008 analysis found that children who had taken paracetamol for a fever during the first year of life had a 50 per cent greater risk of developing asthma symptoms,compared with children who had not taken the drug. The risk rose with increasing use — children who had taken paracetamol at least once a month had a threefold increase in the risk of asthma symptoms.

A study published by British researchers in 2000 using data from the Isaac study found that the prevalence of asthma increased in lock step with sales of paracetamol in the 36 countries examined.

The more paracetamol used in a country,the greater that country’s prevalence of asthma.

A meta-analysis published in 2009 calculated that children who had taken paracetamol in the past year had nearly double the risk of wheezing compared with those who had not taken the drug. “We know that paracetamol can cause increased bronchial constriction and wheezing,” said Mahyar Etminan,a pharmacoepidemiologist at the University of British Columbia and lead author of the study.

Aspirin and other non-steroidal anti-inflammatory drugs,including ibuprofen,are known to provoke asthma attacks in some people,it was noted. Doctors suggest a middle course for parents: Simply use paracetamol (also known as acetaminophen) more sparingly. “We should be reserving paracetamol for very high fevers or for major pain relief,” he said.

“We know that paracetamol is used much more widely than that — when a child is a bit irritable or teething or having an immunisation.”