“A chemical used in plastic that is ubiquitous in the food and drink industries has been linked with emotional and behavioural problems in girls when they are exposed to it before birth,” reported The Independent.
In this study, researchers examined the effects of Bisphenol A (BPA) in 244 mother-child pairs. BPA is a chemical used to manufacture items that come into contact with food, such as food containers, water bottles and protective linings for canned-foods and drinks. The study found that exposure to BPA in pregnancy was associated with increased anxiety, hyperactivity and depression in the offspring, as well as difficulty with modulating emotions and controlling behaviour responses in girls.
This study adds to the body of research on the safety of BPA, but although this was a well-reported study, the study design used for this research can only show association between BPA and the changes in behaviour observed and could not conclude that BPA caused these changes.
So far, the tolerable daily intake for BPA is set at 0.05mg/kg body weight by the European Food Safety Authority (EFSA). Exposure to BPA is currently estimated to be well below this limit. The latest scientific information on BPA is regularly reviewed to see if recommendations need to be changed. The latest information on this review process can be found on the EFSA website.
The food standards agency has a question and answer section on the safety of BPA on its website. The World Health Organization is carrying out a project to review the safety of BPA.
Where did the story come from?
The study was carried out by researchers from the US and Canada, based at Harvard University; the University of North Carolina; the Centres for Disease Control and Prevention; Cincinnati Children’s Hospital Medical Centre; the University of Cincinnati; and Simon Fraser University. It was funded by the National Institute of Environmental Health Sciences and the US Environmental Protection Agency.
The study was published in the peer-reviewed journal Pediatrics.
This story was covered by the Daily Mail, The Daily Telegraph and The Independent. Although the coverage of the research findings is accurate, the Daily Mail and The Telegraph have said in their headline that BPA ‘makes’ girls aggressive, a causal link that has not yet been demonstrated.
What kind of research was this?
This was a cohort study that aimed to examine the impact of gestational (during pregnancy) and childhood exposures to environmental toxins on child development (cognition, behaviour, growth and hearing). Environmental toxins include lead, mercury, pesticides, polychlorinated biphenyls (PCBs), environmental tobacco smoke and alcohol.
In this study, the researchers have examined the effects of exposure to the chemical bisphenol A (BPA). BPA is widely used in production of polycarbonate plastics and epoxy resins. Polycarbonate plastics are used to manufacture items that come into contact with food, such as food containers and water bottles. Epoxy resins are used as protective linings for canned-foods and drinks, therefore most people are exposed to BPA.
Cohort studies are a widely used type of study that assesses whether there is a risk associated with a particular exposure, as it would be unethical to get people to participate in a randomised controlled trial. However, these studies can only show association and are prone to the influence of other factors that could also be linked to the outcomes measured; for example, measures of socioeconomic status or other environmental toxins. Therefore, this study cannot show whether BPA exposure actually causes changes in behaviour.
What did the research involve?
The study involved 244 mother and baby pairs who had sufficient data to be included.
Exposure to BPA was estimated by measuring the concentration of BPA in urine, standardised to the levels of another urine component, creatinine. Urine samples were taken from the mother at 16 weeks and 26 weeks of pregnancy and within 24 hours after giving birth to calculate gestational exposure. Samples were taken from the child at one, two and three years of age to calculate childhood exposure.
The children’s behaviour was assessed at three years of age. A parent-reported scale, called the Behaviour Assessment System for Children 2 (BASC-2) Parent Rating Scale for pre-schoolers, was used. This is an accepted, validated scoring system. Children’s executive functions (including the ability to control emotions and behavioural responses, the ability to plan and organise, and working memory) were also assessed at three years of age. Another parent-reported scale called the Behaviour Rating Inventory of Executive Function-Preschool (BRIEF-P) was used to assess these. On both scales, a higher score indicated greater impairment.
The researchers then looked for associations between BPA concentrations either during gestation or childhood, and behaviour or executive functions. They adjusted for a number of other confounding variables in their analysis, including race, education, income and tobacco smoke. The researchers also analysed the results of boys and girls separately, as previous results have suggested that the results might be different depending on gender.
What were the basic results?
BPA was detected in more than 97% of the gestational urine samples (with an average [median] of 2.0 micrograms per litre) and childhood urine samples (median: 4.1 micrograms per litre).
After taking into account confounding variables, it was seen that gestational BPA concentrations were positively associated with anxiety, hyperactivity and depression in girls at three years of age (BASC-2 scale). However, increasing BPA concentrations were associated with decreasing hyperactivity in boys. No associations were seen between childhood exposure to BPA and aggression, hyperactivity, anxiety, depression, somatisation or attention subscales.
Gestational BPA was also positively associated with emotional control and inhibition scores on the BRIEF-P scale in girls. No associations were seen for boys or for exposure in either girls or boys during childhood.
How did the researchers interpret the results?
The researchers say that, ‘in this study, gestational BPA exposure affected behavioural and emotional regulation domains at three years of age, especially among girls. Clinicians may advise concerned patients to reduce their exposure to certain consumer products, but the benefits of such reductions are unclear.’
This was a cohort study that aimed to examine the affect of exposure to the chemical bisphenol A (BPA) during pregnancy and childhood on behaviour and executive function. It was part of a larger study that looked at the impacts of a range of environment toxins on development (cognition, behaviour, growth and hearing). It found that gestational exposure to BPA was associated with increased anxiety, hyperactivity, depression, and poorer emotional control and inhibition in girls.
However, these results should be interpreted with caution due to the following limitations:
- Cohort studies can only show association, not causation.
- There could be other variables not controlled for that could be responsible for any associations seen. The effects of these might have been mitigated as researchers took into account some environmental toxins. However, they could not take into account all of these and so this still remains a possibility.
- It was a relatively small study with a modest number of participants, with 244 mother-child pairs. As such, the results are more likely to be due to chance than if the study had been carried out in larger numbers of participants.
- This study was part of a larger one that examined many exposure-outcome associations. When a study looks at several different exposures and outcomes, the likelihood of finding chance associations is increased.
- This study adds to the body of research on the safety of BPA, but although it was well-reported, the study design used for this research can only show association between BPA and the changes in behaviour observed and could not conclude that BPA caused these changes.
- So far, the tolerable daily intake for BPA is set at 0.05mg/kg body weight by the European Food Safety Authority (EFSA). Exposure to BPA is currently estimated to be well below this limit. The latest scientific information on BPA is regularly reviewed to see if recommendations need to be changed. The latest information on this review process can be found on the EFSA website.
- The food standards agency has a question and answer section on the safety of BPA on its website. The World Health Organization is carrying out a project to review the safety of BPA.
- Braun JM, Kalkbrenner AE, Calafat AM, et al. Impact of early-life bisphenol a exposure on behavior and executive function in children. Pediatrics 2011, Published online October 24.