"A chemical found in lunchboxes and food cans has been linked to heart disease and diabetes”, The Sun reported. Widespread media interest was given to a study that looked for associations between bisphenol A, a chemical widely used in food and drink packaging, and medical disorders in adults. The newspapers said the study found the risk of heart disease was doubled in those with the highest levels of the chemical, and even small traces in the body were potentially linked to health problems. Some newspapers mentioned the “gender bending” qualities of the chemical and also pointed out it was present in baby bottles.
This study did find significant links between high concentrations of bisphenol A (BPA) in urine and an increased risk of cardiovascular diseases and diabetes. However, this was a cross-sectional study and so can only identify associations, not cause and effect, and so cannot prove that the chemical causes the diseases. Further investigation needs to confirm the findings and look at other issues surrounding it.
There are already regulations in place that limit the amount of BPA that is allowed to migrate into food and these are set at 0.05 mg of BPA per kilo of body weight. In July 2008, The European Food Safety Authority stated that, “after exposure to BPA the human body rapidly metabolises and eliminates the substance”. It also concluded that exposure to BPA is well below the limit, which, “provides a sufficient margin of safety for the protection of the consumer, including foetuses and newborns”. It has also said it will continue to closely monitor the situation.
Where did the story come from?
Dr Iain A. Lang and colleagues from the Peninsula Medical School, the Universities of Exeter and Plymouth, and the University Of Iowa College of Public Health, US carried out the research. Funding was provided by Peninsula College of Medicine and Dentistry, and the lead author was supported by the UK NHS Southwest Region Public Health Training Scheme.
The study was published in the peer-reviewed Journal of the American Medical Association. A supporting editorial by Dr Frederick S. vom Saal and John Peterson Myers was also published in the same journal.
What kind of scientific study was this?
In this cross-sectional study, the authors aimed to investigate associations between bisphenol A (BPA) concentrations in urine and adult health status. The chemical has been shown to have adverse effects on animals and this has led to concern over long-term, low-level exposure in humans.
The researchers used data obtained by the 2003-04 National Health and Nutrition Examination Survey (NHANES), which assessed the health and diet of the general US population. The researchers decided that the diseases they were interested in were rare in children and so limited their analysis to adults aged 18 to 74 years. A third of the NHANES participants were randomly selected and asked to provide urine samples; these were analysed for BPA concentration. This gave a sample size of 1,455 people (694 men and 761 women).
Chronic diseases were assessed using the question: ‘Has a doctor or other health professional ever told you that you have…’ and then a variety of diseases including angina, cancer, stroke, coronary heart disease, heart attack, diabetes, asthma, etc. The researchers grouped certain responses together, such as angina, coronary heart disease and heart attack, which all came under the classification “cardiovascular disease”, and this resulted in eight common chronic disease groups.
Blood samples were also taken and the researchers used these to examine levels of various substances including liver enzymes, lipids and glucose. They used statistical methods to look for associations between the concentration of BPA in urine and chronic disease, taking into account possible confounders such as socioeconomic status, race, education, smoking, BMI, waist circumference and kidney function (which would affect BPA excretion in the urine). They also looked at associations between BPA levels and the results of the blood tests.
What were the results of the study?
Men and women had roughly similar concentrations of BPA in their urine. Other variables that were measured showed slight variations. For example, people who were overweight and obese had higher levels of BPA in their urine than those who were of normal weight. BPA concentration also appeared to increase slightly as educational level and household income decreased. There were also links with certain diseases. After taking into account any potential confounders, an increase in BPA level (by one standard deviation) increased risk of cardiovascular disease by 39% (OR 1.39, 95% CI 1.18 to 1.63) and diabetes by 39% (OR 1.39, 95% CI 1.21 to 1.60).
The researchers found no associations with cancer, arthritis, liver disease, asthma or bronchitis, stroke or thyroid disease. They also found significant associations between raised BPA concentration in urine and raised liver enzymes in the blood.
What interpretations did the researchers draw from these results?
The researchers concluded that higher concentrations of BPA in urine were associated with an increased likelihood of cardiovascular disease, diabetes and liver-enzyme abnormalities.
What does the NHS Knowledge Service make of this study?
This is the first major study to look for any associations between concentrations of bisphenol A in the body and certain chronic diseases. It found associations between the chemical and cardiovascular disease and diabetes but, as the authors acknowledge, this will need to be investigated further. Future studies are needed to confirm these associations and to determine whether they are causal. At present it should be noted that:
- This is a cross-sectional study and as such only looked for relationships between variables. It therefore cannot prove that the raised concentrations of BPA in the participants’ urine caused these chronic diseases. There are many well-established risk factors for these diseases. Prospective cohort studies in people with known BPA exposure levels but without the chronic disease at the beginning of the study are needed to better examine the issue of causality. As stated in the supporting editorial, follow-up of pregnant women and their infants and children would be particularly important due to the possible metabolic effects on growth and development.
- The researchers assessed the presence of chronic disease by asking the participants if they had ever been told by a health professional that they had any disease from a list of diseases. This method could have introduced errors and a more reliable method would have been to confirm these self-reports by looking at the participants medical records or through examination.
- The concentration of BPA in the participants’ urine may not be directly related to the individuals’ actual intake. This is because the physiological mechanisms by which this chemical is processed and excreted by the body may not be the same in all people, as this has not been examined yet. In addition, the single urinary measurement that was taken only represents recent BPA intake.
- No conclusions can be made about the effects of any single type of plastic container, such as plastic water bottles or takeaway containers, as this was not investigated. The chemical is also found in various cans, paper and household products. In particular, there is no basis for the claims that bottle-fed babies are being put at risk. Parents should not be overly concerned.
As the researchers say, further research will be needed to confirm these findings, investigate the reasons for these chronic disease associations, and examine how the chemical is absorbed and processed by the body. Research looking at whether particular food substances or types of plastic packaging can cause increased amounts of BPA taken in by the body is also needed.
Canadian regulatory authorities have already stated that BPA is a toxic chemical and that action should be taken to limit human and environmental exposure. Similar US and other international regulatory boards may take such stands in the future, pending further research.
There are already European regulations in place that limit the amount of BPA that is allowed to migrate into food and these are set at 0.05 mg of BPA per kilo of body weight. In July 2008, The European Food Safety Authority stated that, “after exposure to BPA the human body rapidly metabolises and eliminates the substance”. It also concluded that exposure to BPA is well below the limit, which “provides a sufficient margin of safety for the protection of the consumer, including foetuses and newborns”.
Sir Muir Gray adds…
JAMA is a high quality journal with strict and high standards so we know this is a well-written report of a well-conducted research project. It needs serious consideration by environmental scientists. It won’t change my habits yet, but I try to buy as little plastic as possible, for environmental rather than personal risk reasons.