Food and diet

'Gender bending' plastic bottles

“Drinking from plastic bottles ‘increases exposure to gender-bending chemical’,” The Daily Telegraph has warned. It said that scientists have demonstrated that plastic containers release a chemical called bisphenol A (BPA) into the liquid they contain. The newspaper said that BPA has been shown to interfere with reproductive development in animals and has been linked to cardiovascular disease in humans. It said experts warn that babies are at greater risk because heating the bottles increases the amount of BPA released.

The study behind this report found that after a week of drinking cold beverages mainly from polycarbonate (plastic) bottles, students’ urinary BPA levels were higher than when drinking from stainless-steel containers. The study did not assess the effects of these raised levels. In fact, very few studies have assessed the relationship between exposure to BPA and human health. There is some evidence from animal studies that BPA can affect hormone levels as well as having other effects. However, there are major differences in the way that rats and humans handle BPA, and what happens in rats is not likely to happen in humans.

Where did the story come from?

The study was carried out by Dr Jenny Carwile and colleagues from Harvard School of Public Health, Harvard University Medical School and the Centers for Disease Control and Prevention in Atlanta. The research was supported by the National Institute of Environmental Health Sciences Biological Analysis Core and with grants from Harvard University and Harvard School of Public Health. The study was published in the peer-reviewed medical journal Environmental Health Perspectives .

What kind of scientific study was this?

The chemical bisphenol A (BPA) is commonly used in the production of plastic. Studies suggest that low levels of BPA in animals “and possibly in humans” may cause endocrine disruption, affecting the body’s hormones in some way. According to these researchers, it is unknown whether ingesting food or beverages from plastic containers increases the BPA concentration in humans.

In this non-randomised experiment, researchers recruited Harvard College students aged at least 18 years. The 77 who agreed to participate were provided with stainless-steel containers and asked to use these for all their cold beverages for one week. They were also asked to avoid drinking from plastic bottles during this period. This ‘washout period’ was to ensure that their exposure to BPA in plastic was minimised by the time the study began (orally ingested BPA is rapidly passed through the body, so a week was long enough). The researchers took urine samples from the participants at the end of this period. Each was then given two plastic bottles and asked to drink all cold beverages from them for a week. At the end of this second phase, more urine samples were taken. The participants also completed a quick questionnaire to gauge their compliance with the drinking schedules. The students acted as their own controls in this study, which means that their results after drinking from the polycarbonate bottles were compared with their results after drinking from the stainless steel.

Urine samples were used to determine the concentration of BPA and four other phenols that are found mainly in personal care products (triclosan, methyl paraben, propyl paraben and benzophenone-3). The average concentration of BPA in the group’s urine when drinking from steel containers was compared with that when drinking from plastic. The researchers also analysed these results according to how compliant the participants reported they had been (as a percentage).

What were the results of the study?

The study found that the concentration of BPA in the urine increased by 69% after using the plastic bottles, and that this effect was strongest in people who reported over 90% compliance with the drinking schedules (in whom BPA increased by 77% with polycarbonate bottles). Measurement of the other phenols was used as a check of the BPA measure, as these are not linked with ingestion through drinking. The study found that benzophenone-3 seemed to be associated with the use of polycarbonate bottles.

What interpretations did the researchers draw from these results?

The researchers conclude that this is the first study to quantify the increase in urinary BPA associated with the use of polycarbonate drinking bottles. They say that one week of polycarbonate bottle use increased urinary BPA concentrations by two-thirds.

What does the NHS Knowledge Service make of this study?

This study adds further evidence to the contentious and debated issue of the safety of polycarbonate drinking containers. There are conflicting results and opinions about this, but the Food Standards Agency, an independent government department set up to protect the public’s health in relation to what they eat, has not revised its position on the matter. They state that dietary exposure to BPA is well below levels that would be of concern. Most importantly, the concern about the effects of phenols is based on animal studies, the results of which the FSA says “cannot be readily interpreted as adverse effects”. At present, there is not enough evidence to conclude that BPA affects human hormonal systems, and this study did not assess the effects of the raised levels of BPA on these participants.

As the researchers themselves say, regulations ordering the withdrawal of polycarbonate bottles from some stores and a ban on the use of BPA in baby bottles in Canada are largely “pre-emptive, as no epidemiologic study has evaluated the physiological consequences of polycarbonate bottle use”.

The researchers chose an unusual design to assess this issue. The non-randomised approach where the whole group started with steel containers and then moved to plastic bottles doesn’t allow control for external confounders, which may have meant students did something differently in the first week than they did in the second week that affected the results. There is no reason why the researchers could not have done a randomised cross-over trial in which students are randomly assigned to starting with plastic bottles or steel containers and they then switch over (allowing a suitable washout period before doing so). This would control for the possible differences occurring over time.

The bottom line is that very few studies have assessed the relationship between BPA and human health. While there is some evidence from animal studies that BPA can affect hormone levels in rats and has other effects, there are major differences in the way that rats and humans handle BPA, and what happens in rats is not likely to happen in humans.

NHS Attribution