October 6, 2014

bisphenol-A and children’s lung function

Researchers have published a paper in Jama Pediatrics suggesting a link between exposure to bisphenol-A and asthma symptoms in children. Roundup comments accompanied this before the headlines analysis.

Title, Date of Publication & Journal

Bisphenol A Exposure and the Development of Wheeze and Lung Function in Children Through Age 5 Years

6 October 2014

Jama Paediatrics

Claim supported by evidence?

The paper does not support the claim that BPA exposure causes asthma symptoms, neither in the form of diminished lung function nor persistent wheeze in children

Summary

• Observational study – therefore not able to show a causal effect, only an association which may have an alternative explanation
• A number of potentially important confounding factors have not been considered (e.g. diet, smoking history)
• When all results are taken as a whole, trends are inconsistent, suggesting any single “significant” findings may be due to chance

Study Conclusions

The authors acknowledge that the study’s results are inconsistent but suggest that this is a basis for further research to confirm whether or not BPA exposure is a risk factor for development of asthma.

The strongest effect that they observe is on FEV1 measured in 4-year-olds. However, this effect disappears entirely by the time the same children reach 5 years of age, and isn’t particularly strong to begin with.

Strengths/Limitations

There are many limitations, some of which the authors acknowledge in the paper. However, there are some further limitations:

A lot of data on confounding factors was collected but it is unclear whether these were included in the final models

Nearly 400 mothers were recruited into the study but follow-up data was only collected for a little over 200 infants – we don’t know how different the missing half of the patients are to those that were followed up

Many potential confounding factors were omitted, including diet, and maternal smoking history (although current smoking level was measured)

All the stats are reported using a “10-fold increase in BPA” as the benchmark. However it is unclear whether many 10-fold increases are covered in the data – there may be a few outliers with very high BPA exposure and this may be heavily influencing the results.

The results show many inconsistencies, suggesting that BPA may not be the underlying cause:

• maternal BPA, though not child BPA, is associated with lower FEV1 in 4-year-olds
• even then, that effect has disappeared in 5-year-olds
• wheeze trends are all over the place (maternal BPA concentration is associated with a higher chance of persistent wheeze (sometimes) but not with late-developing wheeze)
• estimates on the effects of maternal BPA on wheeze are very imprecise, probably because there are so many wheeze types identified that there are very few in each

Glossary

FEV1 – forced expiratory volume in one second. It can be measured in litres, but is most commonly expressed as a percentage of a benchmark normal figure based on the patient’s age, sex and height

Any specific expertise relevant to studied paper (beyond statistical)?

Experience of statistical consultancy work on data from respiratory trials.

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