medwireNews: Researchers have found that neonatal hyperbilirubinemia is associated with an increased risk for childhood asthma.
By assessing data from the US Collaborative Perinatal Project, which took place between 1959 and 1965, the team were able to separate the effects of hyperbilirubinemia on asthma risk from those of phototherapy, which has also previously been linked to childhood asthma and was not yet in clinical use at the time of the project.
The analysis included 28,807 term infants who were followed up to the age of 7 years, during which time 5.3% were diagnosed with asthma, reports the team, led by Jun Zhang (Xinhua Hospital, Shanghai, China).
They found that, after adjustment for confounders, the prevalence of asthma significantly correlated with both the maximum total serum bilirubin level (measured around 48 hours postpartum and 24 hours later, and 4–5 days later if >10 mg/dL) and the level 48 hours after birth.
The highest prevalence of asthma was observed in the 2.4% of children with maximum bilirubin levels of greater than 15 mg/dL, at 8.0%. This equated to a 61% increased odds for asthma compared with patients with a maximum bilirubin level of 3 mg/dL or less.
Noting that the magnitude of the relationship between neonatal hyperbilirubinemia and asthma is similar to that in phototherapy-era studies, the researchers say the study “indicates that jaundice, not phototherapy, is associated with asthma.”
They add: “However, the underlying biological mechanisms remain unknown.”
Writing in an accompanying commentary in the American Journal of Epidemiology, Michael Kuzniewicz (Kaiser Permanente Northern California, Oakland, USA) and colleagues say that further research will be needed to determine whether high bilirubin levels cause asthma or there is an underlying genetic predisposition to both conditions.
“This is an important distinction to make before physicians become more aggressive in treating hyperbilirubinemia in hopes of reducing the incidence of asthma,” they write, noting that phototherapy can intervene with child–parent bonding and breastfeeding, as well as resulting in longer hospitalizations.
Other potential interventions that could potentially reduce maximum total serum bilirubin levelsinclude the use of infant formula and heme oxygenase inhibitors. Kuzniewicz et al state that “[b]ecause all of these interventions could plausibly increase the risk of asthma and/or have other significant adverse effects, it is vital that their effects be carefully studied before increasing their use in hopes of preventing asthma.”
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