Asthma affects around 6.8 million children in the US.
The study, published in JAMA Pediatrics, found that prenatal exposure to bisphenol A (BPA) was inconsistently associated with these symptoms, which are closely linked to asthma - the most common chronic disease among children.
BPA is a chemical that is used in some plastics and epoxy resins, and can be found in items ranging from the liners of food cans to store receipts. Such is the prevalence of BPA that the study authors report that most Americans have detectable concentrations of BPA in their urine.
The research team had previously found that prenatal BPA exposure was associated with an increased likelihood of parents reporting wheezing in their children but had not used any objective forms of measurement - such as spirometry testing - to verify that finding.
Exposure to certain chemicals both before and after birth is consistently being identified as a risk factor for the development of respiratory conditions in children. One previous study has linked BPA to the development of asthma in children. Similarly, research elsewhere reported a link between childhood asthma and prenatal exposure to phthalates - chemicals commonly used in plastics and moisturizers.
Measuring lung function and BPA exposure
For the study, the researchers followed 398 mother-infant pairings. In order to assess gestational and child BPA exposure, urine samples were collected twice during pregnancy, and subsequent annual samples were collected from the children.
During their first 5 years, forced expiratory volume (FEV1) testing was used to assess the respiratory status of the children. These results were checked against the participants' BPA exposure to see whether there was an association between lung function and wheezing and the prevalence of the chemical.
The researchers found that for every 10-fold increase in the average maternal urinary BPA concentration, there was an associated 14.2% decrease in the child's predicted FEV1 at 4 years of age. They found no such association, however, when the child was 5 years old.
In addition, every 10-fold increase in the average maternal urinary BPA concentration had a marginal association with a 54.8% increase in the likelihood of the child wheezing. A 10-fold increase in the maternal urinary BPA concentration at 16 weeks of gestation was associated with a 4.27-fold increase in the likelihood of persistent wheezing.
The researchers found no association between the urinary BPA concentrations of the children and their FEV1 or evidence of wheezing.
Further studies needed
These findings are contrary to previous studies. The authors write that one study in particular reported an association of postnatal BPA exposure with child asthma and wheeze, but no association of prenatal BPA exposure.
The authors also state that the study was limited by several factors, most notably that BPA concentration was infrequently measured for a concentration that can vary wildly over time. Also, the participants were not representative of the whole population and may have had poorer lung function than children usually would.
They acknowledge that these reduce the impact of their findings but write that if further research can back them up, it could have important implications for the development of future treatments:
"Additional research is needed to clarify the contrasting findings in recent human studies. If future studies confirm that prenatal BPA exposure may be a risk factor for impaired respiratory health, it may offer another avenue to prevent the development of asthma."
According to the Mayo Clinic, asthma in children is a leading cause of hospitalizations and missed school days, illustrating how disruptive a condition it can be. As yet, the cause of asthma is not fully understood, but current thinking suggests that exposure to tobacco and airborne pollutants is a risk factor.
Experts are regularly finding associations between the health of young children and the health of their parents before they are born. Recently, Medical News Today reported on a study that found there could be an increased asthma risk for babies whose father smoked before their conception.